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-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
- "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
-
-<!-- ****************************************************** -->
-<!-- Header -->
-<!-- ****************************************************** -->
-<book id="Writing-an-ALSA-Driver">
- <bookinfo>
- <title>Writing an ALSA Driver</title>
- <author>
- <firstname>Takashi</firstname>
- <surname>Iwai</surname>
- <affiliation>
- <address>
- <email>tiwai@suse.de</email>
- </address>
- </affiliation>
- </author>
-
- <date>Oct 15, 2007</date>
- <edition>0.3.7</edition>
-
- <abstract>
- <para>
- This document describes how to write an ALSA (Advanced Linux
- Sound Architecture) driver.
- </para>
- </abstract>
-
- <legalnotice>
- <para>
- Copyright (c) 2002-2005 Takashi Iwai <email>tiwai@suse.de</email>
- </para>
-
- <para>
- This document is free; you can redistribute it and/or modify it
- under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
- (at your option) any later version.
- </para>
-
- <para>
- This document is distributed in the hope that it will be useful,
- but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the
- implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A
- PARTICULAR PURPOSE</emphasis>. See the GNU General Public License
- for more details.
- </para>
-
- <para>
- You should have received a copy of the GNU General Public
- License along with this program; if not, write to the Free
- Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
- MA 02111-1307 USA
- </para>
- </legalnotice>
-
- </bookinfo>
-
-<!-- ****************************************************** -->
-<!-- Preface -->
-<!-- ****************************************************** -->
- <preface id="preface">
- <title>Preface</title>
- <para>
- This document describes how to write an
- <ulink url="http://www.alsa-project.org/"><citetitle>
- ALSA (Advanced Linux Sound Architecture)</citetitle></ulink>
- driver. The document focuses mainly on PCI soundcards.
- In the case of other device types, the API might
- be different, too. However, at least the ALSA kernel API is
- consistent, and therefore it would be still a bit help for
- writing them.
- </para>
-
- <para>
- This document targets people who already have enough
- C language skills and have basic linux kernel programming
- knowledge. This document doesn't explain the general
- topic of linux kernel coding and doesn't cover low-level
- driver implementation details. It only describes
- the standard way to write a PCI sound driver on ALSA.
- </para>
-
- <para>
- If you are already familiar with the older ALSA ver.0.5.x API, you
- can check the drivers such as <filename>sound/pci/es1938.c</filename> or
- <filename>sound/pci/maestro3.c</filename> which have also almost the same
- code-base in the ALSA 0.5.x tree, so you can compare the differences.
- </para>
-
- <para>
- This document is still a draft version. Any feedback and
- corrections, please!!
- </para>
- </preface>
-
-
-<!-- ****************************************************** -->
-<!-- File Tree Structure -->
-<!-- ****************************************************** -->
- <chapter id="file-tree">
- <title>File Tree Structure</title>
-
- <section id="file-tree-general">
- <title>General</title>
- <para>
- The ALSA drivers are provided in two ways.
- </para>
-
- <para>
- One is the trees provided as a tarball or via cvs from the
- ALSA's ftp site, and another is the 2.6 (or later) Linux kernel
- tree. To synchronize both, the ALSA driver tree is split into
- two different trees: alsa-kernel and alsa-driver. The former
- contains purely the source code for the Linux 2.6 (or later)
- tree. This tree is designed only for compilation on 2.6 or
- later environment. The latter, alsa-driver, contains many subtle
- files for compiling ALSA drivers outside of the Linux kernel tree,
- wrapper functions for older 2.2 and 2.4 kernels, to adapt the latest kernel API,
- and additional drivers which are still in development or in
- tests. The drivers in alsa-driver tree will be moved to
- alsa-kernel (and eventually to the 2.6 kernel tree) when they are
- finished and confirmed to work fine.
- </para>
-
- <para>
- The file tree structure of ALSA driver is depicted below. Both
- alsa-kernel and alsa-driver have almost the same file
- structure, except for <quote>core</quote> directory. It's
- named as <quote>acore</quote> in alsa-driver tree.
-
- <example>
- <title>ALSA File Tree Structure</title>
- <literallayout>
- sound
- /core
- /oss
- /seq
- /oss
- /instr
- /ioctl32
- /include
- /drivers
- /mpu401
- /opl3
- /i2c
- /l3
- /synth
- /emux
- /pci
- /(cards)
- /isa
- /(cards)
- /arm
- /ppc
- /sparc
- /usb
- /pcmcia /(cards)
- /oss
- </literallayout>
- </example>
- </para>
- </section>
-
- <section id="file-tree-core-directory">
- <title>core directory</title>
- <para>
- This directory contains the middle layer which is the heart
- of ALSA drivers. In this directory, the native ALSA modules are
- stored. The sub-directories contain different modules and are
- dependent upon the kernel config.
- </para>
-
- <section id="file-tree-core-directory-oss">
- <title>core/oss</title>
-
- <para>
- The codes for PCM and mixer OSS emulation modules are stored
- in this directory. The rawmidi OSS emulation is included in
- the ALSA rawmidi code since it's quite small. The sequencer
- code is stored in <filename>core/seq/oss</filename> directory (see
- <link linkend="file-tree-core-directory-seq-oss"><citetitle>
- below</citetitle></link>).
- </para>
- </section>
-
- <section id="file-tree-core-directory-ioctl32">
- <title>core/ioctl32</title>
-
- <para>
- This directory contains the 32bit-ioctl wrappers for 64bit
- architectures such like x86-64, ppc64 and sparc64. For 32bit
- and alpha architectures, these are not compiled.
- </para>
- </section>
-
- <section id="file-tree-core-directory-seq">
- <title>core/seq</title>
- <para>
- This directory and its sub-directories are for the ALSA
- sequencer. This directory contains the sequencer core and
- primary sequencer modules such like snd-seq-midi,
- snd-seq-virmidi, etc. They are compiled only when
- <constant>CONFIG_SND_SEQUENCER</constant> is set in the kernel
- config.
- </para>
- </section>
-
- <section id="file-tree-core-directory-seq-oss">
- <title>core/seq/oss</title>
- <para>
- This contains the OSS sequencer emulation codes.
- </para>
- </section>
-
- <section id="file-tree-core-directory-deq-instr">
- <title>core/seq/instr</title>
- <para>
- This directory contains the modules for the sequencer
- instrument layer.
- </para>
- </section>
- </section>
-
- <section id="file-tree-include-directory">
- <title>include directory</title>
- <para>
- This is the place for the public header files of ALSA drivers,
- which are to be exported to user-space, or included by
- several files at different directories. Basically, the private
- header files should not be placed in this directory, but you may
- still find files there, due to historical reasons :)
- </para>
- </section>
-
- <section id="file-tree-drivers-directory">
- <title>drivers directory</title>
- <para>
- This directory contains code shared among different drivers
- on different architectures. They are hence supposed not to be
- architecture-specific.
- For example, the dummy pcm driver and the serial MIDI
- driver are found in this directory. In the sub-directories,
- there is code for components which are independent from
- bus and cpu architectures.
- </para>
-
- <section id="file-tree-drivers-directory-mpu401">
- <title>drivers/mpu401</title>
- <para>
- The MPU401 and MPU401-UART modules are stored here.
- </para>
- </section>
-
- <section id="file-tree-drivers-directory-opl3">
- <title>drivers/opl3 and opl4</title>
- <para>
- The OPL3 and OPL4 FM-synth stuff is found here.
- </para>
- </section>
- </section>
-
- <section id="file-tree-i2c-directory">
- <title>i2c directory</title>
- <para>
- This contains the ALSA i2c components.
- </para>
-
- <para>
- Although there is a standard i2c layer on Linux, ALSA has its
- own i2c code for some cards, because the soundcard needs only a
- simple operation and the standard i2c API is too complicated for
- such a purpose.
- </para>
-
- <section id="file-tree-i2c-directory-l3">
- <title>i2c/l3</title>
- <para>
- This is a sub-directory for ARM L3 i2c.
- </para>
- </section>
- </section>
-
- <section id="file-tree-synth-directory">
- <title>synth directory</title>
- <para>
- This contains the synth middle-level modules.
- </para>
-
- <para>
- So far, there is only Emu8000/Emu10k1 synth driver under
- the <filename>synth/emux</filename> sub-directory.
- </para>
- </section>
-
- <section id="file-tree-pci-directory">
- <title>pci directory</title>
- <para>
- This directory and its sub-directories hold the top-level card modules
- for PCI soundcards and the code specific to the PCI BUS.
- </para>
-
- <para>
- The drivers compiled from a single file are stored directly
- in the pci directory, while the drivers with several source files are
- stored on their own sub-directory (e.g. emu10k1, ice1712).
- </para>
- </section>
-
- <section id="file-tree-isa-directory">
- <title>isa directory</title>
- <para>
- This directory and its sub-directories hold the top-level card modules
- for ISA soundcards.
- </para>
- </section>
-
- <section id="file-tree-arm-ppc-sparc-directories">
- <title>arm, ppc, and sparc directories</title>
- <para>
- They are used for top-level card modules which are
- specific to one of these architectures.
- </para>
- </section>
-
- <section id="file-tree-usb-directory">
- <title>usb directory</title>
- <para>
- This directory contains the USB-audio driver. In the latest version, the
- USB MIDI driver is integrated in the usb-audio driver.
- </para>
- </section>
-
- <section id="file-tree-pcmcia-directory">
- <title>pcmcia directory</title>
- <para>
- The PCMCIA, especially PCCard drivers will go here. CardBus
- drivers will be in the pci directory, because their API is identical
- to that of standard PCI cards.
- </para>
- </section>
-
- <section id="file-tree-oss-directory">
- <title>oss directory</title>
- <para>
- The OSS/Lite source files are stored here in Linux 2.6 (or
- later) tree. In the ALSA driver tarball, this directory is empty,
- of course :)
- </para>
- </section>
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Basic Flow for PCI Drivers -->
-<!-- ****************************************************** -->
- <chapter id="basic-flow">
- <title>Basic Flow for PCI Drivers</title>
-
- <section id="basic-flow-outline">
- <title>Outline</title>
- <para>
- The minimum flow for PCI soundcards is as follows:
-
- <itemizedlist>
- <listitem><para>define the PCI ID table (see the section
- <link linkend="pci-resource-entries"><citetitle>PCI Entries
- </citetitle></link>).</para></listitem>
- <listitem><para>create <function>probe()</function> callback.</para></listitem>
- <listitem><para>create <function>remove()</function> callback.</para></listitem>
- <listitem><para>create a <structname>pci_driver</structname> structure
- containing the three pointers above.</para></listitem>
- <listitem><para>create an <function>init()</function> function just calling
- the <function>pci_register_driver()</function> to register the pci_driver table
- defined above.</para></listitem>
- <listitem><para>create an <function>exit()</function> function to call
- the <function>pci_unregister_driver()</function> function.</para></listitem>
- </itemizedlist>
- </para>
- </section>
-
- <section id="basic-flow-example">
- <title>Full Code Example</title>
- <para>
- The code example is shown below. Some parts are kept
- unimplemented at this moment but will be filled in the
- next sections. The numbers in the comment lines of the
- <function>snd_mychip_probe()</function> function
- refer to details explained in the following section.
-
- <example>
- <title>Basic Flow for PCI Drivers - Example</title>
- <programlisting>
-<![CDATA[
- #include <linux/init.h>
- #include <linux/pci.h>
- #include <linux/slab.h>
- #include <sound/core.h>
- #include <sound/initval.h>
-
- /* module parameters (see "Module Parameters") */
- /* SNDRV_CARDS: maximum number of cards supported by this module */
- static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
- static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
- static bool enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
-
- /* definition of the chip-specific record */
- struct mychip {
- struct snd_card *card;
- /* the rest of the implementation will be in section
- * "PCI Resource Management"
- */
- };
-
- /* chip-specific destructor
- * (see "PCI Resource Management")
- */
- static int snd_mychip_free(struct mychip *chip)
- {
- .... /* will be implemented later... */
- }
-
- /* component-destructor
- * (see "Management of Cards and Components")
- */
- static int snd_mychip_dev_free(struct snd_device *device)
- {
- return snd_mychip_free(device->device_data);
- }
-
- /* chip-specific constructor
- * (see "Management of Cards and Components")
- */
- static int __devinit snd_mychip_create(struct snd_card *card,
- struct pci_dev *pci,
- struct mychip **rchip)
- {
- struct mychip *chip;
- int err;
- static struct snd_device_ops ops = {
- .dev_free = snd_mychip_dev_free,
- };
-
- *rchip = NULL;
-
- /* check PCI availability here
- * (see "PCI Resource Management")
- */
- ....
-
- /* allocate a chip-specific data with zero filled */
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
- if (chip == NULL)
- return -ENOMEM;
-
- chip->card = card;
-
- /* rest of initialization here; will be implemented
- * later, see "PCI Resource Management"
- */
- ....
-
- err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
- if (err < 0) {
- snd_mychip_free(chip);
- return err;
- }
-
- snd_card_set_dev(card, &pci->dev);
-
- *rchip = chip;
- return 0;
- }
-
- /* constructor -- see "Constructor" sub-section */
- static int __devinit snd_mychip_probe(struct pci_dev *pci,
- const struct pci_device_id *pci_id)
- {
- static int dev;
- struct snd_card *card;
- struct mychip *chip;
- int err;
-
- /* (1) */
- if (dev >= SNDRV_CARDS)
- return -ENODEV;
- if (!enable[dev]) {
- dev++;
- return -ENOENT;
- }
-
- /* (2) */
- err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
- if (err < 0)
- return err;
-
- /* (3) */
- err = snd_mychip_create(card, pci, &chip);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-
- /* (4) */
- strcpy(card->driver, "My Chip");
- strcpy(card->shortname, "My Own Chip 123");
- sprintf(card->longname, "%s at 0x%lx irq %i",
- card->shortname, chip->ioport, chip->irq);
-
- /* (5) */
- .... /* implemented later */
-
- /* (6) */
- err = snd_card_register(card);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-
- /* (7) */
- pci_set_drvdata(pci, card);
- dev++;
- return 0;
- }
-
- /* destructor -- see the "Destructor" sub-section */
- static void __devexit snd_mychip_remove(struct pci_dev *pci)
- {
- snd_card_free(pci_get_drvdata(pci));
- pci_set_drvdata(pci, NULL);
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="basic-flow-constructor">
- <title>Constructor</title>
- <para>
- The real constructor of PCI drivers is the <function>probe</function> callback.
- The <function>probe</function> callback and other component-constructors which are called
- from the <function>probe</function> callback should be defined with
- the <parameter>__devinit</parameter> prefix. You
- cannot use the <parameter>__init</parameter> prefix for them,
- because any PCI device could be a hotplug device.
- </para>
-
- <para>
- In the <function>probe</function> callback, the following scheme is often used.
- </para>
-
- <section id="basic-flow-constructor-device-index">
- <title>1) Check and increment the device index.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int dev;
- ....
- if (dev >= SNDRV_CARDS)
- return -ENODEV;
- if (!enable[dev]) {
- dev++;
- return -ENOENT;
- }
-]]>
- </programlisting>
- </informalexample>
-
- where enable[dev] is the module option.
- </para>
-
- <para>
- Each time the <function>probe</function> callback is called, check the
- availability of the device. If not available, simply increment
- the device index and returns. dev will be incremented also
- later (<link
- linkend="basic-flow-constructor-set-pci"><citetitle>step
- 7</citetitle></link>).
- </para>
- </section>
-
- <section id="basic-flow-constructor-create-card">
- <title>2) Create a card instance</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_card *card;
- int err;
- ....
- err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The details will be explained in the section
- <link linkend="card-management-card-instance"><citetitle>
- Management of Cards and Components</citetitle></link>.
- </para>
- </section>
-
- <section id="basic-flow-constructor-create-main">
- <title>3) Create a main component</title>
- <para>
- In this part, the PCI resources are allocated.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip *chip;
- ....
- err = snd_mychip_create(card, pci, &chip);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-]]>
- </programlisting>
- </informalexample>
-
- The details will be explained in the section <link
- linkend="pci-resource"><citetitle>PCI Resource
- Management</citetitle></link>.
- </para>
- </section>
-
- <section id="basic-flow-constructor-main-component">
- <title>4) Set the driver ID and name strings.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- strcpy(card->driver, "My Chip");
- strcpy(card->shortname, "My Own Chip 123");
- sprintf(card->longname, "%s at 0x%lx irq %i",
- card->shortname, chip->ioport, chip->irq);
-]]>
- </programlisting>
- </informalexample>
-
- The driver field holds the minimal ID string of the
- chip. This is used by alsa-lib's configurator, so keep it
- simple but unique.
- Even the same driver can have different driver IDs to
- distinguish the functionality of each chip type.
- </para>
-
- <para>
- The shortname field is a string shown as more verbose
- name. The longname field contains the information
- shown in <filename>/proc/asound/cards</filename>.
- </para>
- </section>
-
- <section id="basic-flow-constructor-create-other">
- <title>5) Create other components, such as mixer, MIDI, etc.</title>
- <para>
- Here you define the basic components such as
- <link linkend="pcm-interface"><citetitle>PCM</citetitle></link>,
- mixer (e.g. <link linkend="api-ac97"><citetitle>AC97</citetitle></link>),
- MIDI (e.g. <link linkend="midi-interface"><citetitle>MPU-401</citetitle></link>),
- and other interfaces.
- Also, if you want a <link linkend="proc-interface"><citetitle>proc
- file</citetitle></link>, define it here, too.
- </para>
- </section>
-
- <section id="basic-flow-constructor-register-card">
- <title>6) Register the card instance.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- err = snd_card_register(card);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Will be explained in the section <link
- linkend="card-management-registration"><citetitle>Management
- of Cards and Components</citetitle></link>, too.
- </para>
- </section>
-
- <section id="basic-flow-constructor-set-pci">
- <title>7) Set the PCI driver data and return zero.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- pci_set_drvdata(pci, card);
- dev++;
- return 0;
-]]>
- </programlisting>
- </informalexample>
-
- In the above, the card record is stored. This pointer is
- used in the remove callback and power-management
- callbacks, too.
- </para>
- </section>
- </section>
-
- <section id="basic-flow-destructor">
- <title>Destructor</title>
- <para>
- The destructor, remove callback, simply releases the card
- instance. Then the ALSA middle layer will release all the
- attached components automatically.
- </para>
-
- <para>
- It would be typically like the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void __devexit snd_mychip_remove(struct pci_dev *pci)
- {
- snd_card_free(pci_get_drvdata(pci));
- pci_set_drvdata(pci, NULL);
- }
-]]>
- </programlisting>
- </informalexample>
-
- The above code assumes that the card pointer is set to the PCI
- driver data.
- </para>
- </section>
-
- <section id="basic-flow-header-files">
- <title>Header Files</title>
- <para>
- For the above example, at least the following include files
- are necessary.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #include <linux/init.h>
- #include <linux/pci.h>
- #include <linux/slab.h>
- #include <sound/core.h>
- #include <sound/initval.h>
-]]>
- </programlisting>
- </informalexample>
-
- where the last one is necessary only when module options are
- defined in the source file. If the code is split into several
- files, the files without module options don't need them.
- </para>
-
- <para>
- In addition to these headers, you'll need
- <filename>&lt;linux/interrupt.h&gt;</filename> for interrupt
- handling, and <filename>&lt;asm/io.h&gt;</filename> for I/O
- access. If you use the <function>mdelay()</function> or
- <function>udelay()</function> functions, you'll need to include
- <filename>&lt;linux/delay.h&gt;</filename> too.
- </para>
-
- <para>
- The ALSA interfaces like the PCM and control APIs are defined in other
- <filename>&lt;sound/xxx.h&gt;</filename> header files.
- They have to be included after
- <filename>&lt;sound/core.h&gt;</filename>.
- </para>
-
- </section>
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Management of Cards and Components -->
-<!-- ****************************************************** -->
- <chapter id="card-management">
- <title>Management of Cards and Components</title>
-
- <section id="card-management-card-instance">
- <title>Card Instance</title>
- <para>
- For each soundcard, a <quote>card</quote> record must be allocated.
- </para>
-
- <para>
- A card record is the headquarters of the soundcard. It manages
- the whole list of devices (components) on the soundcard, such as
- PCM, mixers, MIDI, synthesizer, and so on. Also, the card
- record holds the ID and the name strings of the card, manages
- the root of proc files, and controls the power-management states
- and hotplug disconnections. The component list on the card
- record is used to manage the correct release of resources at
- destruction.
- </para>
-
- <para>
- As mentioned above, to create a card instance, call
- <function>snd_card_create()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_card *card;
- int err;
- err = snd_card_create(index, id, module, extra_size, &card);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The function takes five arguments, the card-index number, the
- id string, the module pointer (usually
- <constant>THIS_MODULE</constant>),
- the size of extra-data space, and the pointer to return the
- card instance. The extra_size argument is used to
- allocate card-&gt;private_data for the
- chip-specific data. Note that these data
- are allocated by <function>snd_card_create()</function>.
- </para>
- </section>
-
- <section id="card-management-component">
- <title>Components</title>
- <para>
- After the card is created, you can attach the components
- (devices) to the card instance. In an ALSA driver, a component is
- represented as a struct <structname>snd_device</structname> object.
- A component can be a PCM instance, a control interface, a raw
- MIDI interface, etc. Each such instance has one component
- entry.
- </para>
-
- <para>
- A component can be created via
- <function>snd_device_new()</function> function.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_device_new(card, SNDRV_DEV_XXX, chip, &ops);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This takes the card pointer, the device-level
- (<constant>SNDRV_DEV_XXX</constant>), the data pointer, and the
- callback pointers (<parameter>&amp;ops</parameter>). The
- device-level defines the type of components and the order of
- registration and de-registration. For most components, the
- device-level is already defined. For a user-defined component,
- you can use <constant>SNDRV_DEV_LOWLEVEL</constant>.
- </para>
-
- <para>
- This function itself doesn't allocate the data space. The data
- must be allocated manually beforehand, and its pointer is passed
- as the argument. This pointer is used as the
- (<parameter>chip</parameter> identifier in the above example)
- for the instance.
- </para>
-
- <para>
- Each pre-defined ALSA component such as ac97 and pcm calls
- <function>snd_device_new()</function> inside its
- constructor. The destructor for each component is defined in the
- callback pointers. Hence, you don't need to take care of
- calling a destructor for such a component.
- </para>
-
- <para>
- If you wish to create your own component, you need to
- set the destructor function to the dev_free callback in
- the <parameter>ops</parameter>, so that it can be released
- automatically via <function>snd_card_free()</function>.
- The next example will show an implementation of chip-specific
- data.
- </para>
- </section>
-
- <section id="card-management-chip-specific">
- <title>Chip-Specific Data</title>
- <para>
- Chip-specific information, e.g. the I/O port address, its
- resource pointer, or the irq number, is stored in the
- chip-specific record.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- ....
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In general, there are two ways of allocating the chip record.
- </para>
-
- <section id="card-management-chip-specific-snd-card-new">
- <title>1. Allocating via <function>snd_card_create()</function>.</title>
- <para>
- As mentioned above, you can pass the extra-data-length
- to the 4th argument of <function>snd_card_create()</function>, i.e.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = snd_card_create(index[dev], id[dev], THIS_MODULE,
- sizeof(struct mychip), &card);
-]]>
- </programlisting>
- </informalexample>
-
- struct <structname>mychip</structname> is the type of the chip record.
- </para>
-
- <para>
- In return, the allocated record can be accessed as
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip *chip = card->private_data;
-]]>
- </programlisting>
- </informalexample>
-
- With this method, you don't have to allocate twice.
- The record is released together with the card instance.
- </para>
- </section>
-
- <section id="card-management-chip-specific-allocate-extra">
- <title>2. Allocating an extra device.</title>
-
- <para>
- After allocating a card instance via
- <function>snd_card_create()</function> (with
- <constant>0</constant> on the 4th arg), call
- <function>kzalloc()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_card *card;
- struct mychip *chip;
- err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
- .....
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The chip record should have the field to hold the card
- pointer at least,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- struct snd_card *card;
- ....
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Then, set the card pointer in the returned chip instance.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- chip->card = card;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Next, initialize the fields, and register this chip
- record as a low-level device with a specified
- <parameter>ops</parameter>,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_device_ops ops = {
- .dev_free = snd_mychip_dev_free,
- };
- ....
- snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
-]]>
- </programlisting>
- </informalexample>
-
- <function>snd_mychip_dev_free()</function> is the
- device-destructor function, which will call the real
- destructor.
- </para>
-
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_mychip_dev_free(struct snd_device *device)
- {
- return snd_mychip_free(device->device_data);
- }
-]]>
- </programlisting>
- </informalexample>
-
- where <function>snd_mychip_free()</function> is the real destructor.
- </para>
- </section>
- </section>
-
- <section id="card-management-registration">
- <title>Registration and Release</title>
- <para>
- After all components are assigned, register the card instance
- by calling <function>snd_card_register()</function>. Access
- to the device files is enabled at this point. That is, before
- <function>snd_card_register()</function> is called, the
- components are safely inaccessible from external side. If this
- call fails, exit the probe function after releasing the card via
- <function>snd_card_free()</function>.
- </para>
-
- <para>
- For releasing the card instance, you can call simply
- <function>snd_card_free()</function>. As mentioned earlier, all
- components are released automatically by this call.
- </para>
-
- <para>
- As further notes, the destructors (both
- <function>snd_mychip_dev_free</function> and
- <function>snd_mychip_free</function>) cannot be defined with
- the <parameter>__devexit</parameter> prefix, because they may be
- called from the constructor, too, at the false path.
- </para>
-
- <para>
- For a device which allows hotplugging, you can use
- <function>snd_card_free_when_closed</function>. This one will
- postpone the destruction until all devices are closed.
- </para>
-
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- PCI Resource Management -->
-<!-- ****************************************************** -->
- <chapter id="pci-resource">
- <title>PCI Resource Management</title>
-
- <section id="pci-resource-example">
- <title>Full Code Example</title>
- <para>
- In this section, we'll complete the chip-specific constructor,
- destructor and PCI entries. Example code is shown first,
- below.
-
- <example>
- <title>PCI Resource Management Example</title>
- <programlisting>
-<![CDATA[
- struct mychip {
- struct snd_card *card;
- struct pci_dev *pci;
-
- unsigned long port;
- int irq;
- };
-
- static int snd_mychip_free(struct mychip *chip)
- {
- /* disable hardware here if any */
- .... /* (not implemented in this document) */
-
- /* release the irq */
- if (chip->irq >= 0)
- free_irq(chip->irq, chip);
- /* release the I/O ports & memory */
- pci_release_regions(chip->pci);
- /* disable the PCI entry */
- pci_disable_device(chip->pci);
- /* release the data */
- kfree(chip);
- return 0;
- }
-
- /* chip-specific constructor */
- static int __devinit snd_mychip_create(struct snd_card *card,
- struct pci_dev *pci,
- struct mychip **rchip)
- {
- struct mychip *chip;
- int err;
- static struct snd_device_ops ops = {
- .dev_free = snd_mychip_dev_free,
- };
-
- *rchip = NULL;
-
- /* initialize the PCI entry */
- err = pci_enable_device(pci);
- if (err < 0)
- return err;
- /* check PCI availability (28bit DMA) */
- if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
- pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
- printk(KERN_ERR "error to set 28bit mask DMA\n");
- pci_disable_device(pci);
- return -ENXIO;
- }
-
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
- if (chip == NULL) {
- pci_disable_device(pci);
- return -ENOMEM;
- }
-
- /* initialize the stuff */
- chip->card = card;
- chip->pci = pci;
- chip->irq = -1;
-
- /* (1) PCI resource allocation */
- err = pci_request_regions(pci, "My Chip");
- if (err < 0) {
- kfree(chip);
- pci_disable_device(pci);
- return err;
- }
- chip->port = pci_resource_start(pci, 0);
- if (request_irq(pci->irq, snd_mychip_interrupt,
- IRQF_SHARED, KBUILD_MODNAME, chip)) {
- printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
- snd_mychip_free(chip);
- return -EBUSY;
- }
- chip->irq = pci->irq;
-
- /* (2) initialization of the chip hardware */
- .... /* (not implemented in this document) */
-
- err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
- if (err < 0) {
- snd_mychip_free(chip);
- return err;
- }
-
- snd_card_set_dev(card, &pci->dev);
-
- *rchip = chip;
- return 0;
- }
-
- /* PCI IDs */
- static struct pci_device_id snd_mychip_ids[] = {
- { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
- PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
- ....
- { 0, }
- };
- MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
-
- /* pci_driver definition */
- static struct pci_driver driver = {
- .name = KBUILD_MODNAME,
- .id_table = snd_mychip_ids,
- .probe = snd_mychip_probe,
- .remove = __devexit_p(snd_mychip_remove),
- };
-
- /* module initialization */
- static int __init alsa_card_mychip_init(void)
- {
- return pci_register_driver(&driver);
- }
-
- /* module clean up */
- static void __exit alsa_card_mychip_exit(void)
- {
- pci_unregister_driver(&driver);
- }
-
- module_init(alsa_card_mychip_init)
- module_exit(alsa_card_mychip_exit)
-
- EXPORT_NO_SYMBOLS; /* for old kernels only */
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pci-resource-some-haftas">
- <title>Some Hafta's</title>
- <para>
- The allocation of PCI resources is done in the
- <function>probe()</function> function, and usually an extra
- <function>xxx_create()</function> function is written for this
- purpose.
- </para>
-
- <para>
- In the case of PCI devices, you first have to call
- the <function>pci_enable_device()</function> function before
- allocating resources. Also, you need to set the proper PCI DMA
- mask to limit the accessed I/O range. In some cases, you might
- need to call <function>pci_set_master()</function> function,
- too.
- </para>
-
- <para>
- Suppose the 28bit mask, and the code to be added would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = pci_enable_device(pci);
- if (err < 0)
- return err;
- if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
- pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
- printk(KERN_ERR "error to set 28bit mask DMA\n");
- pci_disable_device(pci);
- return -ENXIO;
- }
-
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="pci-resource-resource-allocation">
- <title>Resource Allocation</title>
- <para>
- The allocation of I/O ports and irqs is done via standard kernel
- functions. Unlike ALSA ver.0.5.x., there are no helpers for
- that. And these resources must be released in the destructor
- function (see below). Also, on ALSA 0.9.x, you don't need to
- allocate (pseudo-)DMA for PCI like in ALSA 0.5.x.
- </para>
-
- <para>
- Now assume that the PCI device has an I/O port with 8 bytes
- and an interrupt. Then struct <structname>mychip</structname> will have the
- following fields:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- struct snd_card *card;
-
- unsigned long port;
- int irq;
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For an I/O port (and also a memory region), you need to have
- the resource pointer for the standard resource management. For
- an irq, you have to keep only the irq number (integer). But you
- need to initialize this number as -1 before actual allocation,
- since irq 0 is valid. The port address and its resource pointer
- can be initialized as null by
- <function>kzalloc()</function> automatically, so you
- don't have to take care of resetting them.
- </para>
-
- <para>
- The allocation of an I/O port is done like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = pci_request_regions(pci, "My Chip");
- if (err < 0) {
- kfree(chip);
- pci_disable_device(pci);
- return err;
- }
- chip->port = pci_resource_start(pci, 0);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <!-- obsolete -->
- It will reserve the I/O port region of 8 bytes of the given
- PCI device. The returned value, chip-&gt;res_port, is allocated
- via <function>kmalloc()</function> by
- <function>request_region()</function>. The pointer must be
- released via <function>kfree()</function>, but there is a
- problem with this. This issue will be explained later.
- </para>
-
- <para>
- The allocation of an interrupt source is done like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- if (request_irq(pci->irq, snd_mychip_interrupt,
- IRQF_SHARED, KBUILD_MODNAME, chip)) {
- printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
- snd_mychip_free(chip);
- return -EBUSY;
- }
- chip->irq = pci->irq;
-]]>
- </programlisting>
- </informalexample>
-
- where <function>snd_mychip_interrupt()</function> is the
- interrupt handler defined <link
- linkend="pcm-interface-interrupt-handler"><citetitle>later</citetitle></link>.
- Note that chip-&gt;irq should be defined
- only when <function>request_irq()</function> succeeded.
- </para>
-
- <para>
- On the PCI bus, interrupts can be shared. Thus,
- <constant>IRQF_SHARED</constant> is used as the interrupt flag of
- <function>request_irq()</function>.
- </para>
-
- <para>
- The last argument of <function>request_irq()</function> is the
- data pointer passed to the interrupt handler. Usually, the
- chip-specific record is used for that, but you can use what you
- like, too.
- </para>
-
- <para>
- I won't give details about the interrupt handler at this
- point, but at least its appearance can be explained now. The
- interrupt handler looks usually like the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
- {
- struct mychip *chip = dev_id;
- ....
- return IRQ_HANDLED;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Now let's write the corresponding destructor for the resources
- above. The role of destructor is simple: disable the hardware
- (if already activated) and release the resources. So far, we
- have no hardware part, so the disabling code is not written here.
- </para>
-
- <para>
- To release the resources, the <quote>check-and-release</quote>
- method is a safer way. For the interrupt, do like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- if (chip->irq >= 0)
- free_irq(chip->irq, chip);
-]]>
- </programlisting>
- </informalexample>
-
- Since the irq number can start from 0, you should initialize
- chip-&gt;irq with a negative value (e.g. -1), so that you can
- check the validity of the irq number as above.
- </para>
-
- <para>
- When you requested I/O ports or memory regions via
- <function>pci_request_region()</function> or
- <function>pci_request_regions()</function> like in this example,
- release the resource(s) using the corresponding function,
- <function>pci_release_region()</function> or
- <function>pci_release_regions()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- pci_release_regions(chip->pci);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- When you requested manually via <function>request_region()</function>
- or <function>request_mem_region</function>, you can release it via
- <function>release_resource()</function>. Suppose that you keep
- the resource pointer returned from <function>request_region()</function>
- in chip-&gt;res_port, the release procedure looks like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- release_and_free_resource(chip->res_port);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Don't forget to call <function>pci_disable_device()</function>
- before the end.
- </para>
-
- <para>
- And finally, release the chip-specific record.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- kfree(chip);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Again, remember that you cannot
- use the <parameter>__devexit</parameter> prefix for this destructor.
- </para>
-
- <para>
- We didn't implement the hardware disabling part in the above.
- If you need to do this, please note that the destructor may be
- called even before the initialization of the chip is completed.
- It would be better to have a flag to skip hardware disabling
- if the hardware was not initialized yet.
- </para>
-
- <para>
- When the chip-data is assigned to the card using
- <function>snd_device_new()</function> with
- <constant>SNDRV_DEV_LOWLELVEL</constant> , its destructor is
- called at the last. That is, it is assured that all other
- components like PCMs and controls have already been released.
- You don't have to stop PCMs, etc. explicitly, but just
- call low-level hardware stopping.
- </para>
-
- <para>
- The management of a memory-mapped region is almost as same as
- the management of an I/O port. You'll need three fields like
- the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- ....
- unsigned long iobase_phys;
- void __iomem *iobase_virt;
- };
-]]>
- </programlisting>
- </informalexample>
-
- and the allocation would be like below:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- if ((err = pci_request_regions(pci, "My Chip")) < 0) {
- kfree(chip);
- return err;
- }
- chip->iobase_phys = pci_resource_start(pci, 0);
- chip->iobase_virt = ioremap_nocache(chip->iobase_phys,
- pci_resource_len(pci, 0));
-]]>
- </programlisting>
- </informalexample>
-
- and the corresponding destructor would be:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_mychip_free(struct mychip *chip)
- {
- ....
- if (chip->iobase_virt)
- iounmap(chip->iobase_virt);
- ....
- pci_release_regions(chip->pci);
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- </section>
-
- <section id="pci-resource-device-struct">
- <title>Registration of Device Struct</title>
- <para>
- At some point, typically after calling <function>snd_device_new()</function>,
- you need to register the struct <structname>device</structname> of the chip
- you're handling for udev and co. ALSA provides a macro for compatibility with
- older kernels. Simply call like the following:
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_card_set_dev(card, &pci->dev);
-]]>
- </programlisting>
- </informalexample>
- so that it stores the PCI's device pointer to the card. This will be
- referred by ALSA core functions later when the devices are registered.
- </para>
- <para>
- In the case of non-PCI, pass the proper device struct pointer of the BUS
- instead. (In the case of legacy ISA without PnP, you don't have to do
- anything.)
- </para>
- </section>
-
- <section id="pci-resource-entries">
- <title>PCI Entries</title>
- <para>
- So far, so good. Let's finish the missing PCI
- stuff. At first, we need a
- <structname>pci_device_id</structname> table for this
- chipset. It's a table of PCI vendor/device ID number, and some
- masks.
- </para>
-
- <para>
- For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct pci_device_id snd_mychip_ids[] = {
- { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
- PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
- ....
- { 0, }
- };
- MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first and second fields of
- the <structname>pci_device_id</structname> structure are the vendor and
- device IDs. If you have no reason to filter the matching
- devices, you can leave the remaining fields as above. The last
- field of the <structname>pci_device_id</structname> struct contains
- private data for this entry. You can specify any value here, for
- example, to define specific operations for supported device IDs.
- Such an example is found in the intel8x0 driver.
- </para>
-
- <para>
- The last entry of this list is the terminator. You must
- specify this all-zero entry.
- </para>
-
- <para>
- Then, prepare the <structname>pci_driver</structname> record:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct pci_driver driver = {
- .name = KBUILD_MODNAME,
- .id_table = snd_mychip_ids,
- .probe = snd_mychip_probe,
- .remove = __devexit_p(snd_mychip_remove),
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The <structfield>probe</structfield> and
- <structfield>remove</structfield> functions have already
- been defined in the previous sections.
- The <structfield>remove</structfield> function should
- be defined with the
- <function>__devexit_p()</function> macro, so that it's not
- defined for built-in (and non-hot-pluggable) case. The
- <structfield>name</structfield>
- field is the name string of this device. Note that you must not
- use a slash <quote>/</quote> in this string.
- </para>
-
- <para>
- And at last, the module entries:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int __init alsa_card_mychip_init(void)
- {
- return pci_register_driver(&driver);
- }
-
- static void __exit alsa_card_mychip_exit(void)
- {
- pci_unregister_driver(&driver);
- }
-
- module_init(alsa_card_mychip_init)
- module_exit(alsa_card_mychip_exit)
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Note that these module entries are tagged with
- <parameter>__init</parameter> and
- <parameter>__exit</parameter> prefixes, not
- <parameter>__devinit</parameter> nor
- <parameter>__devexit</parameter>.
- </para>
-
- <para>
- Oh, one thing was forgotten. If you have no exported symbols,
- you need to declare it in 2.2 or 2.4 kernels (it's not necessary in 2.6 kernels).
-
- <informalexample>
- <programlisting>
-<![CDATA[
- EXPORT_NO_SYMBOLS;
-]]>
- </programlisting>
- </informalexample>
-
- That's all!
- </para>
- </section>
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- PCM Interface -->
-<!-- ****************************************************** -->
- <chapter id="pcm-interface">
- <title>PCM Interface</title>
-
- <section id="pcm-interface-general">
- <title>General</title>
- <para>
- The PCM middle layer of ALSA is quite powerful and it is only
- necessary for each driver to implement the low-level functions
- to access its hardware.
- </para>
-
- <para>
- For accessing to the PCM layer, you need to include
- <filename>&lt;sound/pcm.h&gt;</filename> first. In addition,
- <filename>&lt;sound/pcm_params.h&gt;</filename> might be needed
- if you access to some functions related with hw_param.
- </para>
-
- <para>
- Each card device can have up to four pcm instances. A pcm
- instance corresponds to a pcm device file. The limitation of
- number of instances comes only from the available bit size of
- the Linux's device numbers. Once when 64bit device number is
- used, we'll have more pcm instances available.
- </para>
-
- <para>
- A pcm instance consists of pcm playback and capture streams,
- and each pcm stream consists of one or more pcm substreams. Some
- soundcards support multiple playback functions. For example,
- emu10k1 has a PCM playback of 32 stereo substreams. In this case, at
- each open, a free substream is (usually) automatically chosen
- and opened. Meanwhile, when only one substream exists and it was
- already opened, the successful open will either block
- or error with <constant>EAGAIN</constant> according to the
- file open mode. But you don't have to care about such details in your
- driver. The PCM middle layer will take care of such work.
- </para>
- </section>
-
- <section id="pcm-interface-example">
- <title>Full Code Example</title>
- <para>
- The example code below does not include any hardware access
- routines but shows only the skeleton, how to build up the PCM
- interfaces.
-
- <example>
- <title>PCM Example Code</title>
- <programlisting>
-<![CDATA[
- #include <sound/pcm.h>
- ....
-
- /* hardware definition */
- static struct snd_pcm_hardware snd_mychip_playback_hw = {
- .info = (SNDRV_PCM_INFO_MMAP |
- SNDRV_PCM_INFO_INTERLEAVED |
- SNDRV_PCM_INFO_BLOCK_TRANSFER |
- SNDRV_PCM_INFO_MMAP_VALID),
- .formats = SNDRV_PCM_FMTBIT_S16_LE,
- .rates = SNDRV_PCM_RATE_8000_48000,
- .rate_min = 8000,
- .rate_max = 48000,
- .channels_min = 2,
- .channels_max = 2,
- .buffer_bytes_max = 32768,
- .period_bytes_min = 4096,
- .period_bytes_max = 32768,
- .periods_min = 1,
- .periods_max = 1024,
- };
-
- /* hardware definition */
- static struct snd_pcm_hardware snd_mychip_capture_hw = {
- .info = (SNDRV_PCM_INFO_MMAP |
- SNDRV_PCM_INFO_INTERLEAVED |
- SNDRV_PCM_INFO_BLOCK_TRANSFER |
- SNDRV_PCM_INFO_MMAP_VALID),
- .formats = SNDRV_PCM_FMTBIT_S16_LE,
- .rates = SNDRV_PCM_RATE_8000_48000,
- .rate_min = 8000,
- .rate_max = 48000,
- .channels_min = 2,
- .channels_max = 2,
- .buffer_bytes_max = 32768,
- .period_bytes_min = 4096,
- .period_bytes_max = 32768,
- .periods_min = 1,
- .periods_max = 1024,
- };
-
- /* open callback */
- static int snd_mychip_playback_open(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- runtime->hw = snd_mychip_playback_hw;
- /* more hardware-initialization will be done here */
- ....
- return 0;
- }
-
- /* close callback */
- static int snd_mychip_playback_close(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- /* the hardware-specific codes will be here */
- ....
- return 0;
-
- }
-
- /* open callback */
- static int snd_mychip_capture_open(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- runtime->hw = snd_mychip_capture_hw;
- /* more hardware-initialization will be done here */
- ....
- return 0;
- }
-
- /* close callback */
- static int snd_mychip_capture_close(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- /* the hardware-specific codes will be here */
- ....
- return 0;
-
- }
-
- /* hw_params callback */
- static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream,
- struct snd_pcm_hw_params *hw_params)
- {
- return snd_pcm_lib_malloc_pages(substream,
- params_buffer_bytes(hw_params));
- }
-
- /* hw_free callback */
- static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream)
- {
- return snd_pcm_lib_free_pages(substream);
- }
-
- /* prepare callback */
- static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- /* set up the hardware with the current configuration
- * for example...
- */
- mychip_set_sample_format(chip, runtime->format);
- mychip_set_sample_rate(chip, runtime->rate);
- mychip_set_channels(chip, runtime->channels);
- mychip_set_dma_setup(chip, runtime->dma_addr,
- chip->buffer_size,
- chip->period_size);
- return 0;
- }
-
- /* trigger callback */
- static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream,
- int cmd)
- {
- switch (cmd) {
- case SNDRV_PCM_TRIGGER_START:
- /* do something to start the PCM engine */
- ....
- break;
- case SNDRV_PCM_TRIGGER_STOP:
- /* do something to stop the PCM engine */
- ....
- break;
- default:
- return -EINVAL;
- }
- }
-
- /* pointer callback */
- static snd_pcm_uframes_t
- snd_mychip_pcm_pointer(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- unsigned int current_ptr;
-
- /* get the current hardware pointer */
- current_ptr = mychip_get_hw_pointer(chip);
- return current_ptr;
- }
-
- /* operators */
- static struct snd_pcm_ops snd_mychip_playback_ops = {
- .open = snd_mychip_playback_open,
- .close = snd_mychip_playback_close,
- .ioctl = snd_pcm_lib_ioctl,
- .hw_params = snd_mychip_pcm_hw_params,
- .hw_free = snd_mychip_pcm_hw_free,
- .prepare = snd_mychip_pcm_prepare,
- .trigger = snd_mychip_pcm_trigger,
- .pointer = snd_mychip_pcm_pointer,
- };
-
- /* operators */
- static struct snd_pcm_ops snd_mychip_capture_ops = {
- .open = snd_mychip_capture_open,
- .close = snd_mychip_capture_close,
- .ioctl = snd_pcm_lib_ioctl,
- .hw_params = snd_mychip_pcm_hw_params,
- .hw_free = snd_mychip_pcm_hw_free,
- .prepare = snd_mychip_pcm_prepare,
- .trigger = snd_mychip_pcm_trigger,
- .pointer = snd_mychip_pcm_pointer,
- };
-
- /*
- * definitions of capture are omitted here...
- */
-
- /* create a pcm device */
- static int __devinit snd_mychip_new_pcm(struct mychip *chip)
- {
- struct snd_pcm *pcm;
- int err;
-
- err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
- if (err < 0)
- return err;
- pcm->private_data = chip;
- strcpy(pcm->name, "My Chip");
- chip->pcm = pcm;
- /* set operators */
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
- &snd_mychip_playback_ops);
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
- &snd_mychip_capture_ops);
- /* pre-allocation of buffers */
- /* NOTE: this may fail */
- snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
- snd_dma_pci_data(chip->pci),
- 64*1024, 64*1024);
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-constructor">
- <title>Constructor</title>
- <para>
- A pcm instance is allocated by the <function>snd_pcm_new()</function>
- function. It would be better to create a constructor for pcm,
- namely,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int __devinit snd_mychip_new_pcm(struct mychip *chip)
- {
- struct snd_pcm *pcm;
- int err;
-
- err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
- if (err < 0)
- return err;
- pcm->private_data = chip;
- strcpy(pcm->name, "My Chip");
- chip->pcm = pcm;
- ....
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The <function>snd_pcm_new()</function> function takes four
- arguments. The first argument is the card pointer to which this
- pcm is assigned, and the second is the ID string.
- </para>
-
- <para>
- The third argument (<parameter>index</parameter>, 0 in the
- above) is the index of this new pcm. It begins from zero. If
- you create more than one pcm instances, specify the
- different numbers in this argument. For example,
- <parameter>index</parameter> = 1 for the second PCM device.
- </para>
-
- <para>
- The fourth and fifth arguments are the number of substreams
- for playback and capture, respectively. Here 1 is used for
- both arguments. When no playback or capture substreams are available,
- pass 0 to the corresponding argument.
- </para>
-
- <para>
- If a chip supports multiple playbacks or captures, you can
- specify more numbers, but they must be handled properly in
- open/close, etc. callbacks. When you need to know which
- substream you are referring to, then it can be obtained from
- struct <structname>snd_pcm_substream</structname> data passed to each callback
- as follows:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_pcm_substream *substream;
- int index = substream->number;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- After the pcm is created, you need to set operators for each
- pcm stream.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
- &snd_mychip_playback_ops);
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
- &snd_mychip_capture_ops);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The operators are defined typically like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_pcm_ops snd_mychip_playback_ops = {
- .open = snd_mychip_pcm_open,
- .close = snd_mychip_pcm_close,
- .ioctl = snd_pcm_lib_ioctl,
- .hw_params = snd_mychip_pcm_hw_params,
- .hw_free = snd_mychip_pcm_hw_free,
- .prepare = snd_mychip_pcm_prepare,
- .trigger = snd_mychip_pcm_trigger,
- .pointer = snd_mychip_pcm_pointer,
- };
-]]>
- </programlisting>
- </informalexample>
-
- All the callbacks are described in the
- <link linkend="pcm-interface-operators"><citetitle>
- Operators</citetitle></link> subsection.
- </para>
-
- <para>
- After setting the operators, you probably will want to
- pre-allocate the buffer. For the pre-allocation, simply call
- the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
- snd_dma_pci_data(chip->pci),
- 64*1024, 64*1024);
-]]>
- </programlisting>
- </informalexample>
-
- It will allocate a buffer up to 64kB as default.
- Buffer management details will be described in the later section <link
- linkend="buffer-and-memory"><citetitle>Buffer and Memory
- Management</citetitle></link>.
- </para>
-
- <para>
- Additionally, you can set some extra information for this pcm
- in pcm-&gt;info_flags.
- The available values are defined as
- <constant>SNDRV_PCM_INFO_XXX</constant> in
- <filename>&lt;sound/asound.h&gt;</filename>, which is used for
- the hardware definition (described later). When your soundchip
- supports only half-duplex, specify like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX;
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="pcm-interface-destructor">
- <title>... And the Destructor?</title>
- <para>
- The destructor for a pcm instance is not always
- necessary. Since the pcm device will be released by the middle
- layer code automatically, you don't have to call the destructor
- explicitly.
- </para>
-
- <para>
- The destructor would be necessary if you created
- special records internally and needed to release them. In such a
- case, set the destructor function to
- pcm-&gt;private_free:
-
- <example>
- <title>PCM Instance with a Destructor</title>
- <programlisting>
-<![CDATA[
- static void mychip_pcm_free(struct snd_pcm *pcm)
- {
- struct mychip *chip = snd_pcm_chip(pcm);
- /* free your own data */
- kfree(chip->my_private_pcm_data);
- /* do what you like else */
- ....
- }
-
- static int __devinit snd_mychip_new_pcm(struct mychip *chip)
- {
- struct snd_pcm *pcm;
- ....
- /* allocate your own data */
- chip->my_private_pcm_data = kmalloc(...);
- /* set the destructor */
- pcm->private_data = chip;
- pcm->private_free = mychip_pcm_free;
- ....
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-runtime">
- <title>Runtime Pointer - The Chest of PCM Information</title>
- <para>
- When the PCM substream is opened, a PCM runtime instance is
- allocated and assigned to the substream. This pointer is
- accessible via <constant>substream-&gt;runtime</constant>.
- This runtime pointer holds most information you need
- to control the PCM: the copy of hw_params and sw_params configurations, the buffer
- pointers, mmap records, spinlocks, etc.
- </para>
-
- <para>
- The definition of runtime instance is found in
- <filename>&lt;sound/pcm.h&gt;</filename>. Here are
- the contents of this file:
- <informalexample>
- <programlisting>
-<![CDATA[
-struct _snd_pcm_runtime {
- /* -- Status -- */
- struct snd_pcm_substream *trigger_master;
- snd_timestamp_t trigger_tstamp; /* trigger timestamp */
- int overrange;
- snd_pcm_uframes_t avail_max;
- snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */
- snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/
-
- /* -- HW params -- */
- snd_pcm_access_t access; /* access mode */
- snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */
- snd_pcm_subformat_t subformat; /* subformat */
- unsigned int rate; /* rate in Hz */
- unsigned int channels; /* channels */
- snd_pcm_uframes_t period_size; /* period size */
- unsigned int periods; /* periods */
- snd_pcm_uframes_t buffer_size; /* buffer size */
- unsigned int tick_time; /* tick time */
- snd_pcm_uframes_t min_align; /* Min alignment for the format */
- size_t byte_align;
- unsigned int frame_bits;
- unsigned int sample_bits;
- unsigned int info;
- unsigned int rate_num;
- unsigned int rate_den;
-
- /* -- SW params -- */
- struct timespec tstamp_mode; /* mmap timestamp is updated */
- unsigned int period_step;
- unsigned int sleep_min; /* min ticks to sleep */
- snd_pcm_uframes_t start_threshold;
- snd_pcm_uframes_t stop_threshold;
- snd_pcm_uframes_t silence_threshold; /* Silence filling happens when
- noise is nearest than this */
- snd_pcm_uframes_t silence_size; /* Silence filling size */
- snd_pcm_uframes_t boundary; /* pointers wrap point */
-
- snd_pcm_uframes_t silenced_start;
- snd_pcm_uframes_t silenced_size;
-
- snd_pcm_sync_id_t sync; /* hardware synchronization ID */
-
- /* -- mmap -- */
- volatile struct snd_pcm_mmap_status *status;
- volatile struct snd_pcm_mmap_control *control;
- atomic_t mmap_count;
-
- /* -- locking / scheduling -- */
- spinlock_t lock;
- wait_queue_head_t sleep;
- struct timer_list tick_timer;
- struct fasync_struct *fasync;
-
- /* -- private section -- */
- void *private_data;
- void (*private_free)(struct snd_pcm_runtime *runtime);
-
- /* -- hardware description -- */
- struct snd_pcm_hardware hw;
- struct snd_pcm_hw_constraints hw_constraints;
-
- /* -- interrupt callbacks -- */
- void (*transfer_ack_begin)(struct snd_pcm_substream *substream);
- void (*transfer_ack_end)(struct snd_pcm_substream *substream);
-
- /* -- timer -- */
- unsigned int timer_resolution; /* timer resolution */
-
- /* -- DMA -- */
- unsigned char *dma_area; /* DMA area */
- dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */
- size_t dma_bytes; /* size of DMA area */
-
- struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */
-
-#if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)
- /* -- OSS things -- */
- struct snd_pcm_oss_runtime oss;
-#endif
-};
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For the operators (callbacks) of each sound driver, most of
- these records are supposed to be read-only. Only the PCM
- middle-layer changes / updates them. The exceptions are
- the hardware description (hw), interrupt callbacks
- (transfer_ack_xxx), DMA buffer information, and the private
- data. Besides, if you use the standard buffer allocation
- method via <function>snd_pcm_lib_malloc_pages()</function>,
- you don't need to set the DMA buffer information by yourself.
- </para>
-
- <para>
- In the sections below, important records are explained.
- </para>
-
- <section id="pcm-interface-runtime-hw">
- <title>Hardware Description</title>
- <para>
- The hardware descriptor (struct <structname>snd_pcm_hardware</structname>)
- contains the definitions of the fundamental hardware
- configuration. Above all, you'll need to define this in
- <link linkend="pcm-interface-operators-open-callback"><citetitle>
- the open callback</citetitle></link>.
- Note that the runtime instance holds the copy of the
- descriptor, not the pointer to the existing descriptor. That
- is, in the open callback, you can modify the copied descriptor
- (<constant>runtime-&gt;hw</constant>) as you need. For example, if the maximum
- number of channels is 1 only on some chip models, you can
- still use the same hardware descriptor and change the
- channels_max later:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_pcm_runtime *runtime = substream->runtime;
- ...
- runtime->hw = snd_mychip_playback_hw; /* common definition */
- if (chip->model == VERY_OLD_ONE)
- runtime->hw.channels_max = 1;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Typically, you'll have a hardware descriptor as below:
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_pcm_hardware snd_mychip_playback_hw = {
- .info = (SNDRV_PCM_INFO_MMAP |
- SNDRV_PCM_INFO_INTERLEAVED |
- SNDRV_PCM_INFO_BLOCK_TRANSFER |
- SNDRV_PCM_INFO_MMAP_VALID),
- .formats = SNDRV_PCM_FMTBIT_S16_LE,
- .rates = SNDRV_PCM_RATE_8000_48000,
- .rate_min = 8000,
- .rate_max = 48000,
- .channels_min = 2,
- .channels_max = 2,
- .buffer_bytes_max = 32768,
- .period_bytes_min = 4096,
- .period_bytes_max = 32768,
- .periods_min = 1,
- .periods_max = 1024,
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <itemizedlist>
- <listitem><para>
- The <structfield>info</structfield> field contains the type and
- capabilities of this pcm. The bit flags are defined in
- <filename>&lt;sound/asound.h&gt;</filename> as
- <constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you
- have to specify whether the mmap is supported and which
- interleaved format is supported.
- When the is supported, add the
- <constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the
- hardware supports the interleaved or the non-interleaved
- formats, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or
- <constant>SNDRV_PCM_INFO_NONINTERLEAVED</constant> flag must
- be set, respectively. If both are supported, you can set both,
- too.
- </para>
-
- <para>
- In the above example, <constant>MMAP_VALID</constant> and
- <constant>BLOCK_TRANSFER</constant> are specified for the OSS mmap
- mode. Usually both are set. Of course,
- <constant>MMAP_VALID</constant> is set only if the mmap is
- really supported.
- </para>
-
- <para>
- The other possible flags are
- <constant>SNDRV_PCM_INFO_PAUSE</constant> and
- <constant>SNDRV_PCM_INFO_RESUME</constant>. The
- <constant>PAUSE</constant> bit means that the pcm supports the
- <quote>pause</quote> operation, while the
- <constant>RESUME</constant> bit means that the pcm supports
- the full <quote>suspend/resume</quote> operation.
- If the <constant>PAUSE</constant> flag is set,
- the <structfield>trigger</structfield> callback below
- must handle the corresponding (pause push/release) commands.
- The suspend/resume trigger commands can be defined even without
- the <constant>RESUME</constant> flag. See <link
- linkend="power-management"><citetitle>
- Power Management</citetitle></link> section for details.
- </para>
-
- <para>
- When the PCM substreams can be synchronized (typically,
- synchronized start/stop of a playback and a capture streams),
- you can give <constant>SNDRV_PCM_INFO_SYNC_START</constant>,
- too. In this case, you'll need to check the linked-list of
- PCM substreams in the trigger callback. This will be
- described in the later section.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>formats</structfield> field contains the bit-flags
- of supported formats (<constant>SNDRV_PCM_FMTBIT_XXX</constant>).
- If the hardware supports more than one format, give all or'ed
- bits. In the example above, the signed 16bit little-endian
- format is specified.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>rates</structfield> field contains the bit-flags of
- supported rates (<constant>SNDRV_PCM_RATE_XXX</constant>).
- When the chip supports continuous rates, pass
- <constant>CONTINUOUS</constant> bit additionally.
- The pre-defined rate bits are provided only for typical
- rates. If your chip supports unconventional rates, you need to add
- the <constant>KNOT</constant> bit and set up the hardware
- constraint manually (explained later).
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>rate_min</structfield> and
- <structfield>rate_max</structfield> define the minimum and
- maximum sample rate. This should correspond somehow to
- <structfield>rates</structfield> bits.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>channel_min</structfield> and
- <structfield>channel_max</structfield>
- define, as you might already expected, the minimum and maximum
- number of channels.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>buffer_bytes_max</structfield> defines the
- maximum buffer size in bytes. There is no
- <structfield>buffer_bytes_min</structfield> field, since
- it can be calculated from the minimum period size and the
- minimum number of periods.
- Meanwhile, <structfield>period_bytes_min</structfield> and
- define the minimum and maximum size of the period in bytes.
- <structfield>periods_max</structfield> and
- <structfield>periods_min</structfield> define the maximum and
- minimum number of periods in the buffer.
- </para>
-
- <para>
- The <quote>period</quote> is a term that corresponds to
- a fragment in the OSS world. The period defines the size at
- which a PCM interrupt is generated. This size strongly
- depends on the hardware.
- Generally, the smaller period size will give you more
- interrupts, that is, more controls.
- In the case of capture, this size defines the input latency.
- On the other hand, the whole buffer size defines the
- output latency for the playback direction.
- </para>
- </listitem>
-
- <listitem>
- <para>
- There is also a field <structfield>fifo_size</structfield>.
- This specifies the size of the hardware FIFO, but currently it
- is neither used in the driver nor in the alsa-lib. So, you
- can ignore this field.
- </para>
- </listitem>
- </itemizedlist>
- </para>
- </section>
-
- <section id="pcm-interface-runtime-config">
- <title>PCM Configurations</title>
- <para>
- Ok, let's go back again to the PCM runtime records.
- The most frequently referred records in the runtime instance are
- the PCM configurations.
- The PCM configurations are stored in the runtime instance
- after the application sends <type>hw_params</type> data via
- alsa-lib. There are many fields copied from hw_params and
- sw_params structs. For example,
- <structfield>format</structfield> holds the format type
- chosen by the application. This field contains the enum value
- <constant>SNDRV_PCM_FORMAT_XXX</constant>.
- </para>
-
- <para>
- One thing to be noted is that the configured buffer and period
- sizes are stored in <quote>frames</quote> in the runtime.
- In the ALSA world, 1 frame = channels * samples-size.
- For conversion between frames and bytes, you can use the
- <function>frames_to_bytes()</function> and
- <function>bytes_to_frames()</function> helper functions.
- <informalexample>
- <programlisting>
-<![CDATA[
- period_bytes = frames_to_bytes(runtime, runtime->period_size);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Also, many software parameters (sw_params) are
- stored in frames, too. Please check the type of the field.
- <type>snd_pcm_uframes_t</type> is for the frames as unsigned
- integer while <type>snd_pcm_sframes_t</type> is for the frames
- as signed integer.
- </para>
- </section>
-
- <section id="pcm-interface-runtime-dma">
- <title>DMA Buffer Information</title>
- <para>
- The DMA buffer is defined by the following four fields,
- <structfield>dma_area</structfield>,
- <structfield>dma_addr</structfield>,
- <structfield>dma_bytes</structfield> and
- <structfield>dma_private</structfield>.
- The <structfield>dma_area</structfield> holds the buffer
- pointer (the logical address). You can call
- <function>memcpy</function> from/to
- this pointer. Meanwhile, <structfield>dma_addr</structfield>
- holds the physical address of the buffer. This field is
- specified only when the buffer is a linear buffer.
- <structfield>dma_bytes</structfield> holds the size of buffer
- in bytes. <structfield>dma_private</structfield> is used for
- the ALSA DMA allocator.
- </para>
-
- <para>
- If you use a standard ALSA function,
- <function>snd_pcm_lib_malloc_pages()</function>, for
- allocating the buffer, these fields are set by the ALSA middle
- layer, and you should <emphasis>not</emphasis> change them by
- yourself. You can read them but not write them.
- On the other hand, if you want to allocate the buffer by
- yourself, you'll need to manage it in hw_params callback.
- At least, <structfield>dma_bytes</structfield> is mandatory.
- <structfield>dma_area</structfield> is necessary when the
- buffer is mmapped. If your driver doesn't support mmap, this
- field is not necessary. <structfield>dma_addr</structfield>
- is also optional. You can use
- <structfield>dma_private</structfield> as you like, too.
- </para>
- </section>
-
- <section id="pcm-interface-runtime-status">
- <title>Running Status</title>
- <para>
- The running status can be referred via <constant>runtime-&gt;status</constant>.
- This is the pointer to the struct <structname>snd_pcm_mmap_status</structname>
- record. For example, you can get the current DMA hardware
- pointer via <constant>runtime-&gt;status-&gt;hw_ptr</constant>.
- </para>
-
- <para>
- The DMA application pointer can be referred via
- <constant>runtime-&gt;control</constant>, which points to the
- struct <structname>snd_pcm_mmap_control</structname> record.
- However, accessing directly to this value is not recommended.
- </para>
- </section>
-
- <section id="pcm-interface-runtime-private">
- <title>Private Data</title>
- <para>
- You can allocate a record for the substream and store it in
- <constant>runtime-&gt;private_data</constant>. Usually, this
- is done in
- <link linkend="pcm-interface-operators-open-callback"><citetitle>
- the open callback</citetitle></link>.
- Don't mix this with <constant>pcm-&gt;private_data</constant>.
- The <constant>pcm-&gt;private_data</constant> usually points to the
- chip instance assigned statically at the creation of PCM, while the
- <constant>runtime-&gt;private_data</constant> points to a dynamic
- data structure created at the PCM open callback.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_pcm_substream *substream)
- {
- struct my_pcm_data *data;
- ....
- data = kmalloc(sizeof(*data), GFP_KERNEL);
- substream->runtime->private_data = data;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The allocated object must be released in
- <link linkend="pcm-interface-operators-open-callback"><citetitle>
- the close callback</citetitle></link>.
- </para>
- </section>
-
- <section id="pcm-interface-runtime-intr">
- <title>Interrupt Callbacks</title>
- <para>
- The field <structfield>transfer_ack_begin</structfield> and
- <structfield>transfer_ack_end</structfield> are called at
- the beginning and at the end of
- <function>snd_pcm_period_elapsed()</function>, respectively.
- </para>
- </section>
-
- </section>
-
- <section id="pcm-interface-operators">
- <title>Operators</title>
- <para>
- OK, now let me give details about each pcm callback
- (<parameter>ops</parameter>). In general, every callback must
- return 0 if successful, or a negative error number
- such as <constant>-EINVAL</constant>. To choose an appropriate
- error number, it is advised to check what value other parts of
- the kernel return when the same kind of request fails.
- </para>
-
- <para>
- The callback function takes at least the argument with
- <structname>snd_pcm_substream</structname> pointer. To retrieve
- the chip record from the given substream instance, you can use the
- following macro.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- int xxx() {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- ....
- }
-]]>
- </programlisting>
- </informalexample>
-
- The macro reads <constant>substream-&gt;private_data</constant>,
- which is a copy of <constant>pcm-&gt;private_data</constant>.
- You can override the former if you need to assign different data
- records per PCM substream. For example, the cmi8330 driver assigns
- different private_data for playback and capture directions,
- because it uses two different codecs (SB- and AD-compatible) for
- different directions.
- </para>
-
- <section id="pcm-interface-operators-open-callback">
- <title>open callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- This is called when a pcm substream is opened.
- </para>
-
- <para>
- At least, here you have to initialize the runtime-&gt;hw
- record. Typically, this is done by like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- runtime->hw = snd_mychip_playback_hw;
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
-
- where <parameter>snd_mychip_playback_hw</parameter> is the
- pre-defined hardware description.
- </para>
-
- <para>
- You can allocate a private data in this callback, as described
- in <link linkend="pcm-interface-runtime-private"><citetitle>
- Private Data</citetitle></link> section.
- </para>
-
- <para>
- If the hardware configuration needs more constraints, set the
- hardware constraints here, too.
- See <link linkend="pcm-interface-constraints"><citetitle>
- Constraints</citetitle></link> for more details.
- </para>
- </section>
-
- <section id="pcm-interface-operators-close-callback">
- <title>close callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_close(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- Obviously, this is called when a pcm substream is closed.
- </para>
-
- <para>
- Any private instance for a pcm substream allocated in the
- open callback will be released here.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_close(struct snd_pcm_substream *substream)
- {
- ....
- kfree(substream->runtime->private_data);
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="pcm-interface-operators-ioctl-callback">
- <title>ioctl callback</title>
- <para>
- This is used for any special call to pcm ioctls. But
- usually you can pass a generic ioctl callback,
- <function>snd_pcm_lib_ioctl</function>.
- </para>
- </section>
-
- <section id="pcm-interface-operators-hw-params-callback">
- <title>hw_params callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_hw_params(struct snd_pcm_substream *substream,
- struct snd_pcm_hw_params *hw_params);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This is called when the hardware parameter
- (<structfield>hw_params</structfield>) is set
- up by the application,
- that is, once when the buffer size, the period size, the
- format, etc. are defined for the pcm substream.
- </para>
-
- <para>
- Many hardware setups should be done in this callback,
- including the allocation of buffers.
- </para>
-
- <para>
- Parameters to be initialized are retrieved by
- <function>params_xxx()</function> macros. To allocate
- buffer, you can call a helper function,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params));
-]]>
- </programlisting>
- </informalexample>
-
- <function>snd_pcm_lib_malloc_pages()</function> is available
- only when the DMA buffers have been pre-allocated.
- See the section <link
- linkend="buffer-and-memory-buffer-types"><citetitle>
- Buffer Types</citetitle></link> for more details.
- </para>
-
- <para>
- Note that this and <structfield>prepare</structfield> callbacks
- may be called multiple times per initialization.
- For example, the OSS emulation may
- call these callbacks at each change via its ioctl.
- </para>
-
- <para>
- Thus, you need to be careful not to allocate the same buffers
- many times, which will lead to memory leaks! Calling the
- helper function above many times is OK. It will release the
- previous buffer automatically when it was already allocated.
- </para>
-
- <para>
- Another note is that this callback is non-atomic
- (schedulable). This is important, because the
- <structfield>trigger</structfield> callback
- is atomic (non-schedulable). That is, mutexes or any
- schedule-related functions are not available in
- <structfield>trigger</structfield> callback.
- Please see the subsection
- <link linkend="pcm-interface-atomicity"><citetitle>
- Atomicity</citetitle></link> for details.
- </para>
- </section>
-
- <section id="pcm-interface-operators-hw-free-callback">
- <title>hw_free callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_hw_free(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This is called to release the resources allocated via
- <structfield>hw_params</structfield>. For example, releasing the
- buffer via
- <function>snd_pcm_lib_malloc_pages()</function> is done by
- calling the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_free_pages(substream);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This function is always called before the close callback is called.
- Also, the callback may be called multiple times, too.
- Keep track whether the resource was already released.
- </para>
- </section>
-
- <section id="pcm-interface-operators-prepare-callback">
- <title>prepare callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_prepare(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This callback is called when the pcm is
- <quote>prepared</quote>. You can set the format type, sample
- rate, etc. here. The difference from
- <structfield>hw_params</structfield> is that the
- <structfield>prepare</structfield> callback will be called each
- time
- <function>snd_pcm_prepare()</function> is called, i.e. when
- recovering after underruns, etc.
- </para>
-
- <para>
- Note that this callback is now non-atomic.
- You can use schedule-related functions safely in this callback.
- </para>
-
- <para>
- In this and the following callbacks, you can refer to the
- values via the runtime record,
- substream-&gt;runtime.
- For example, to get the current
- rate, format or channels, access to
- runtime-&gt;rate,
- runtime-&gt;format or
- runtime-&gt;channels, respectively.
- The physical address of the allocated buffer is set to
- runtime-&gt;dma_area. The buffer and period sizes are
- in runtime-&gt;buffer_size and runtime-&gt;period_size,
- respectively.
- </para>
-
- <para>
- Be careful that this callback will be called many times at
- each setup, too.
- </para>
- </section>
-
- <section id="pcm-interface-operators-trigger-callback">
- <title>trigger callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd);
-]]>
- </programlisting>
- </informalexample>
-
- This is called when the pcm is started, stopped or paused.
- </para>
-
- <para>
- Which action is specified in the second argument,
- <constant>SNDRV_PCM_TRIGGER_XXX</constant> in
- <filename>&lt;sound/pcm.h&gt;</filename>. At least,
- the <constant>START</constant> and <constant>STOP</constant>
- commands must be defined in this callback.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- switch (cmd) {
- case SNDRV_PCM_TRIGGER_START:
- /* do something to start the PCM engine */
- break;
- case SNDRV_PCM_TRIGGER_STOP:
- /* do something to stop the PCM engine */
- break;
- default:
- return -EINVAL;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- When the pcm supports the pause operation (given in the info
- field of the hardware table), the <constant>PAUSE_PUSE</constant>
- and <constant>PAUSE_RELEASE</constant> commands must be
- handled here, too. The former is the command to pause the pcm,
- and the latter to restart the pcm again.
- </para>
-
- <para>
- When the pcm supports the suspend/resume operation,
- regardless of full or partial suspend/resume support,
- the <constant>SUSPEND</constant> and <constant>RESUME</constant>
- commands must be handled, too.
- These commands are issued when the power-management status is
- changed. Obviously, the <constant>SUSPEND</constant> and
- <constant>RESUME</constant> commands
- suspend and resume the pcm substream, and usually, they
- are identical to the <constant>STOP</constant> and
- <constant>START</constant> commands, respectively.
- See the <link linkend="power-management"><citetitle>
- Power Management</citetitle></link> section for details.
- </para>
-
- <para>
- As mentioned, this callback is atomic. You cannot call
- functions which may sleep.
- The trigger callback should be as minimal as possible,
- just really triggering the DMA. The other stuff should be
- initialized hw_params and prepare callbacks properly
- beforehand.
- </para>
- </section>
-
- <section id="pcm-interface-operators-pointer-callback">
- <title>pointer callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream)
-]]>
- </programlisting>
- </informalexample>
-
- This callback is called when the PCM middle layer inquires
- the current hardware position on the buffer. The position must
- be returned in frames,
- ranging from 0 to buffer_size - 1.
- </para>
-
- <para>
- This is called usually from the buffer-update routine in the
- pcm middle layer, which is invoked when
- <function>snd_pcm_period_elapsed()</function> is called in the
- interrupt routine. Then the pcm middle layer updates the
- position and calculates the available space, and wakes up the
- sleeping poll threads, etc.
- </para>
-
- <para>
- This callback is also atomic.
- </para>
- </section>
-
- <section id="pcm-interface-operators-copy-silence">
- <title>copy and silence callbacks</title>
- <para>
- These callbacks are not mandatory, and can be omitted in
- most cases. These callbacks are used when the hardware buffer
- cannot be in the normal memory space. Some chips have their
- own buffer on the hardware which is not mappable. In such a
- case, you have to transfer the data manually from the memory
- buffer to the hardware buffer. Or, if the buffer is
- non-contiguous on both physical and virtual memory spaces,
- these callbacks must be defined, too.
- </para>
-
- <para>
- If these two callbacks are defined, copy and set-silence
- operations are done by them. The detailed will be described in
- the later section <link
- linkend="buffer-and-memory"><citetitle>Buffer and Memory
- Management</citetitle></link>.
- </para>
- </section>
-
- <section id="pcm-interface-operators-ack">
- <title>ack callback</title>
- <para>
- This callback is also not mandatory. This callback is called
- when the appl_ptr is updated in read or write operations.
- Some drivers like emu10k1-fx and cs46xx need to track the
- current appl_ptr for the internal buffer, and this callback
- is useful only for such a purpose.
- </para>
- <para>
- This callback is atomic.
- </para>
- </section>
-
- <section id="pcm-interface-operators-page-callback">
- <title>page callback</title>
-
- <para>
- This callback is optional too. This callback is used
- mainly for non-contiguous buffers. The mmap calls this
- callback to get the page address. Some examples will be
- explained in the later section <link
- linkend="buffer-and-memory"><citetitle>Buffer and Memory
- Management</citetitle></link>, too.
- </para>
- </section>
- </section>
-
- <section id="pcm-interface-interrupt-handler">
- <title>Interrupt Handler</title>
- <para>
- The rest of pcm stuff is the PCM interrupt handler. The
- role of PCM interrupt handler in the sound driver is to update
- the buffer position and to tell the PCM middle layer when the
- buffer position goes across the prescribed period size. To
- inform this, call the <function>snd_pcm_period_elapsed()</function>
- function.
- </para>
-
- <para>
- There are several types of sound chips to generate the interrupts.
- </para>
-
- <section id="pcm-interface-interrupt-handler-boundary">
- <title>Interrupts at the period (fragment) boundary</title>
- <para>
- This is the most frequently found type: the hardware
- generates an interrupt at each period boundary.
- In this case, you can call
- <function>snd_pcm_period_elapsed()</function> at each
- interrupt.
- </para>
-
- <para>
- <function>snd_pcm_period_elapsed()</function> takes the
- substream pointer as its argument. Thus, you need to keep the
- substream pointer accessible from the chip instance. For
- example, define substream field in the chip record to hold the
- current running substream pointer, and set the pointer value
- at open callback (and reset at close callback).
- </para>
-
- <para>
- If you acquire a spinlock in the interrupt handler, and the
- lock is used in other pcm callbacks, too, then you have to
- release the lock before calling
- <function>snd_pcm_period_elapsed()</function>, because
- <function>snd_pcm_period_elapsed()</function> calls other pcm
- callbacks inside.
- </para>
-
- <para>
- Typical code would be like:
-
- <example>
- <title>Interrupt Handler Case #1</title>
- <programlisting>
-<![CDATA[
- static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
- {
- struct mychip *chip = dev_id;
- spin_lock(&chip->lock);
- ....
- if (pcm_irq_invoked(chip)) {
- /* call updater, unlock before it */
- spin_unlock(&chip->lock);
- snd_pcm_period_elapsed(chip->substream);
- spin_lock(&chip->lock);
- /* acknowledge the interrupt if necessary */
- }
- ....
- spin_unlock(&chip->lock);
- return IRQ_HANDLED;
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-interrupt-handler-timer">
- <title>High frequency timer interrupts</title>
- <para>
- This happense when the hardware doesn't generate interrupts
- at the period boundary but issues timer interrupts at a fixed
- timer rate (e.g. es1968 or ymfpci drivers).
- In this case, you need to check the current hardware
- position and accumulate the processed sample length at each
- interrupt. When the accumulated size exceeds the period
- size, call
- <function>snd_pcm_period_elapsed()</function> and reset the
- accumulator.
- </para>
-
- <para>
- Typical code would be like the following.
-
- <example>
- <title>Interrupt Handler Case #2</title>
- <programlisting>
-<![CDATA[
- static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
- {
- struct mychip *chip = dev_id;
- spin_lock(&chip->lock);
- ....
- if (pcm_irq_invoked(chip)) {
- unsigned int last_ptr, size;
- /* get the current hardware pointer (in frames) */
- last_ptr = get_hw_ptr(chip);
- /* calculate the processed frames since the
- * last update
- */
- if (last_ptr < chip->last_ptr)
- size = runtime->buffer_size + last_ptr
- - chip->last_ptr;
- else
- size = last_ptr - chip->last_ptr;
- /* remember the last updated point */
- chip->last_ptr = last_ptr;
- /* accumulate the size */
- chip->size += size;
- /* over the period boundary? */
- if (chip->size >= runtime->period_size) {
- /* reset the accumulator */
- chip->size %= runtime->period_size;
- /* call updater */
- spin_unlock(&chip->lock);
- snd_pcm_period_elapsed(substream);
- spin_lock(&chip->lock);
- }
- /* acknowledge the interrupt if necessary */
- }
- ....
- spin_unlock(&chip->lock);
- return IRQ_HANDLED;
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-interrupt-handler-both">
- <title>On calling <function>snd_pcm_period_elapsed()</function></title>
- <para>
- In both cases, even if more than one period are elapsed, you
- don't have to call
- <function>snd_pcm_period_elapsed()</function> many times. Call
- only once. And the pcm layer will check the current hardware
- pointer and update to the latest status.
- </para>
- </section>
- </section>
-
- <section id="pcm-interface-atomicity">
- <title>Atomicity</title>
- <para>
- One of the most important (and thus difficult to debug) problems
- in kernel programming are race conditions.
- In the Linux kernel, they are usually avoided via spin-locks, mutexes
- or semaphores. In general, if a race condition can happen
- in an interrupt handler, it has to be managed atomically, and you
- have to use a spinlock to protect the critical session. If the
- critical section is not in interrupt handler code and
- if taking a relatively long time to execute is acceptable, you
- should use mutexes or semaphores instead.
- </para>
-
- <para>
- As already seen, some pcm callbacks are atomic and some are
- not. For example, the <parameter>hw_params</parameter> callback is
- non-atomic, while <parameter>trigger</parameter> callback is
- atomic. This means, the latter is called already in a spinlock
- held by the PCM middle layer. Please take this atomicity into
- account when you choose a locking scheme in the callbacks.
- </para>
-
- <para>
- In the atomic callbacks, you cannot use functions which may call
- <function>schedule</function> or go to
- <function>sleep</function>. Semaphores and mutexes can sleep,
- and hence they cannot be used inside the atomic callbacks
- (e.g. <parameter>trigger</parameter> callback).
- To implement some delay in such a callback, please use
- <function>udelay()</function> or <function>mdelay()</function>.
- </para>
-
- <para>
- All three atomic callbacks (trigger, pointer, and ack) are
- called with local interrupts disabled.
- </para>
-
- </section>
- <section id="pcm-interface-constraints">
- <title>Constraints</title>
- <para>
- If your chip supports unconventional sample rates, or only the
- limited samples, you need to set a constraint for the
- condition.
- </para>
-
- <para>
- For example, in order to restrict the sample rates in the some
- supported values, use
- <function>snd_pcm_hw_constraint_list()</function>.
- You need to call this function in the open callback.
-
- <example>
- <title>Example of Hardware Constraints</title>
- <programlisting>
-<![CDATA[
- static unsigned int rates[] =
- {4000, 10000, 22050, 44100};
- static struct snd_pcm_hw_constraint_list constraints_rates = {
- .count = ARRAY_SIZE(rates),
- .list = rates,
- .mask = 0,
- };
-
- static int snd_mychip_pcm_open(struct snd_pcm_substream *substream)
- {
- int err;
- ....
- err = snd_pcm_hw_constraint_list(substream->runtime, 0,
- SNDRV_PCM_HW_PARAM_RATE,
- &constraints_rates);
- if (err < 0)
- return err;
- ....
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- There are many different constraints.
- Look at <filename>sound/pcm.h</filename> for a complete list.
- You can even define your own constraint rules.
- For example, let's suppose my_chip can manage a substream of 1 channel
- if and only if the format is S16_LE, otherwise it supports any format
- specified in the <structname>snd_pcm_hardware</structname> structure (or in any
- other constraint_list). You can build a rule like this:
-
- <example>
- <title>Example of Hardware Constraints for Channels</title>
- <programlisting>
-<![CDATA[
- static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params,
- struct snd_pcm_hw_rule *rule)
- {
- struct snd_interval *c = hw_param_interval(params,
- SNDRV_PCM_HW_PARAM_CHANNELS);
- struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
- struct snd_mask fmt;
-
- snd_mask_any(&fmt); /* Init the struct */
- if (c->min < 2) {
- fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;
- return snd_mask_refine(f, &fmt);
- }
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- Then you need to call this function to add your rule:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
- hw_rule_channels_by_format, 0, SNDRV_PCM_HW_PARAM_FORMAT,
- -1);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The rule function is called when an application sets the number of
- channels. But an application can set the format before the number of
- channels. Thus you also need to define the inverse rule:
-
- <example>
- <title>Example of Hardware Constraints for Channels</title>
- <programlisting>
-<![CDATA[
- static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params,
- struct snd_pcm_hw_rule *rule)
- {
- struct snd_interval *c = hw_param_interval(params,
- SNDRV_PCM_HW_PARAM_CHANNELS);
- struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
- struct snd_interval ch;
-
- snd_interval_any(&ch);
- if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {
- ch.min = ch.max = 1;
- ch.integer = 1;
- return snd_interval_refine(c, &ch);
- }
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- ...and in the open callback:
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
- hw_rule_format_by_channels, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
- -1);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- I won't give more details here, rather I
- would like to say, <quote>Luke, use the source.</quote>
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Control Interface -->
-<!-- ****************************************************** -->
- <chapter id="control-interface">
- <title>Control Interface</title>
-
- <section id="control-interface-general">
- <title>General</title>
- <para>
- The control interface is used widely for many switches,
- sliders, etc. which are accessed from user-space. Its most
- important use is the mixer interface. In other words, since ALSA
- 0.9.x, all the mixer stuff is implemented on the control kernel API.
- </para>
-
- <para>
- ALSA has a well-defined AC97 control module. If your chip
- supports only the AC97 and nothing else, you can skip this
- section.
- </para>
-
- <para>
- The control API is defined in
- <filename>&lt;sound/control.h&gt;</filename>.
- Include this file if you want to add your own controls.
- </para>
- </section>
-
- <section id="control-interface-definition">
- <title>Definition of Controls</title>
- <para>
- To create a new control, you need to define the
- following three
- callbacks: <structfield>info</structfield>,
- <structfield>get</structfield> and
- <structfield>put</structfield>. Then, define a
- struct <structname>snd_kcontrol_new</structname> record, such as:
-
- <example>
- <title>Definition of a Control</title>
- <programlisting>
-<![CDATA[
- static struct snd_kcontrol_new my_control __devinitdata = {
- .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
- .name = "PCM Playback Switch",
- .index = 0,
- .access = SNDRV_CTL_ELEM_ACCESS_READWRITE,
- .private_value = 0xffff,
- .info = my_control_info,
- .get = my_control_get,
- .put = my_control_put
- };
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- Most likely the control is created via
- <function>snd_ctl_new1()</function>, and in such a case, you can
- add the <parameter>__devinitdata</parameter> prefix to the
- definition as above.
- </para>
-
- <para>
- The <structfield>iface</structfield> field specifies the control
- type, <constant>SNDRV_CTL_ELEM_IFACE_XXX</constant>, which
- is usually <constant>MIXER</constant>.
- Use <constant>CARD</constant> for global controls that are not
- logically part of the mixer.
- If the control is closely associated with some specific device on
- the sound card, use <constant>HWDEP</constant>,
- <constant>PCM</constant>, <constant>RAWMIDI</constant>,
- <constant>TIMER</constant>, or <constant>SEQUENCER</constant>, and
- specify the device number with the
- <structfield>device</structfield> and
- <structfield>subdevice</structfield> fields.
- </para>
-
- <para>
- The <structfield>name</structfield> is the name identifier
- string. Since ALSA 0.9.x, the control name is very important,
- because its role is classified from its name. There are
- pre-defined standard control names. The details are described in
- the <link linkend="control-interface-control-names"><citetitle>
- Control Names</citetitle></link> subsection.
- </para>
-
- <para>
- The <structfield>index</structfield> field holds the index number
- of this control. If there are several different controls with
- the same name, they can be distinguished by the index
- number. This is the case when
- several codecs exist on the card. If the index is zero, you can
- omit the definition above.
- </para>
-
- <para>
- The <structfield>access</structfield> field contains the access
- type of this control. Give the combination of bit masks,
- <constant>SNDRV_CTL_ELEM_ACCESS_XXX</constant>, there.
- The details will be explained in
- the <link linkend="control-interface-access-flags"><citetitle>
- Access Flags</citetitle></link> subsection.
- </para>
-
- <para>
- The <structfield>private_value</structfield> field contains
- an arbitrary long integer value for this record. When using
- the generic <structfield>info</structfield>,
- <structfield>get</structfield> and
- <structfield>put</structfield> callbacks, you can pass a value
- through this field. If several small numbers are necessary, you can
- combine them in bitwise. Or, it's possible to give a pointer
- (casted to unsigned long) of some record to this field, too.
- </para>
-
- <para>
- The <structfield>tlv</structfield> field can be used to provide
- metadata about the control; see the
- <link linkend="control-interface-tlv">
- <citetitle>Metadata</citetitle></link> subsection.
- </para>
-
- <para>
- The other three are
- <link linkend="control-interface-callbacks"><citetitle>
- callback functions</citetitle></link>.
- </para>
- </section>
-
- <section id="control-interface-control-names">
- <title>Control Names</title>
- <para>
- There are some standards to define the control names. A
- control is usually defined from the three parts as
- <quote>SOURCE DIRECTION FUNCTION</quote>.
- </para>
-
- <para>
- The first, <constant>SOURCE</constant>, specifies the source
- of the control, and is a string such as <quote>Master</quote>,
- <quote>PCM</quote>, <quote>CD</quote> and
- <quote>Line</quote>. There are many pre-defined sources.
- </para>
-
- <para>
- The second, <constant>DIRECTION</constant>, is one of the
- following strings according to the direction of the control:
- <quote>Playback</quote>, <quote>Capture</quote>, <quote>Bypass
- Playback</quote> and <quote>Bypass Capture</quote>. Or, it can
- be omitted, meaning both playback and capture directions.
- </para>
-
- <para>
- The third, <constant>FUNCTION</constant>, is one of the
- following strings according to the function of the control:
- <quote>Switch</quote>, <quote>Volume</quote> and
- <quote>Route</quote>.
- </para>
-
- <para>
- The example of control names are, thus, <quote>Master Capture
- Switch</quote> or <quote>PCM Playback Volume</quote>.
- </para>
-
- <para>
- There are some exceptions:
- </para>
-
- <section id="control-interface-control-names-global">
- <title>Global capture and playback</title>
- <para>
- <quote>Capture Source</quote>, <quote>Capture Switch</quote>
- and <quote>Capture Volume</quote> are used for the global
- capture (input) source, switch and volume. Similarly,
- <quote>Playback Switch</quote> and <quote>Playback
- Volume</quote> are used for the global output gain switch and
- volume.
- </para>
- </section>
-
- <section id="control-interface-control-names-tone">
- <title>Tone-controls</title>
- <para>
- tone-control switch and volumes are specified like
- <quote>Tone Control - XXX</quote>, e.g. <quote>Tone Control -
- Switch</quote>, <quote>Tone Control - Bass</quote>,
- <quote>Tone Control - Center</quote>.
- </para>
- </section>
-
- <section id="control-interface-control-names-3d">
- <title>3D controls</title>
- <para>
- 3D-control switches and volumes are specified like <quote>3D
- Control - XXX</quote>, e.g. <quote>3D Control -
- Switch</quote>, <quote>3D Control - Center</quote>, <quote>3D
- Control - Space</quote>.
- </para>
- </section>
-
- <section id="control-interface-control-names-mic">
- <title>Mic boost</title>
- <para>
- Mic-boost switch is set as <quote>Mic Boost</quote> or
- <quote>Mic Boost (6dB)</quote>.
- </para>
-
- <para>
- More precise information can be found in
- <filename>Documentation/sound/alsa/ControlNames.txt</filename>.
- </para>
- </section>
- </section>
-
- <section id="control-interface-access-flags">
- <title>Access Flags</title>
-
- <para>
- The access flag is the bitmask which specifies the access type
- of the given control. The default access type is
- <constant>SNDRV_CTL_ELEM_ACCESS_READWRITE</constant>,
- which means both read and write are allowed to this control.
- When the access flag is omitted (i.e. = 0), it is
- considered as <constant>READWRITE</constant> access as default.
- </para>
-
- <para>
- When the control is read-only, pass
- <constant>SNDRV_CTL_ELEM_ACCESS_READ</constant> instead.
- In this case, you don't have to define
- the <structfield>put</structfield> callback.
- Similarly, when the control is write-only (although it's a rare
- case), you can use the <constant>WRITE</constant> flag instead, and
- you don't need the <structfield>get</structfield> callback.
- </para>
-
- <para>
- If the control value changes frequently (e.g. the VU meter),
- <constant>VOLATILE</constant> flag should be given. This means
- that the control may be changed without
- <link linkend="control-interface-change-notification"><citetitle>
- notification</citetitle></link>. Applications should poll such
- a control constantly.
- </para>
-
- <para>
- When the control is inactive, set
- the <constant>INACTIVE</constant> flag, too.
- There are <constant>LOCK</constant> and
- <constant>OWNER</constant> flags to change the write
- permissions.
- </para>
-
- </section>
-
- <section id="control-interface-callbacks">
- <title>Callbacks</title>
-
- <section id="control-interface-callbacks-info">
- <title>info callback</title>
- <para>
- The <structfield>info</structfield> callback is used to get
- detailed information on this control. This must store the
- values of the given struct <structname>snd_ctl_elem_info</structname>
- object. For example, for a boolean control with a single
- element:
-
- <example>
- <title>Example of info callback</title>
- <programlisting>
-<![CDATA[
- static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_info *uinfo)
- {
- uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
- uinfo->count = 1;
- uinfo->value.integer.min = 0;
- uinfo->value.integer.max = 1;
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- The <structfield>type</structfield> field specifies the type
- of the control. There are <constant>BOOLEAN</constant>,
- <constant>INTEGER</constant>, <constant>ENUMERATED</constant>,
- <constant>BYTES</constant>, <constant>IEC958</constant> and
- <constant>INTEGER64</constant>. The
- <structfield>count</structfield> field specifies the
- number of elements in this control. For example, a stereo
- volume would have count = 2. The
- <structfield>value</structfield> field is a union, and
- the values stored are depending on the type. The boolean and
- integer types are identical.
- </para>
-
- <para>
- The enumerated type is a bit different from others. You'll
- need to set the string for the currently given item index.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_info *uinfo)
- {
- static char *texts[4] = {
- "First", "Second", "Third", "Fourth"
- };
- uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
- uinfo->count = 1;
- uinfo->value.enumerated.items = 4;
- if (uinfo->value.enumerated.item > 3)
- uinfo->value.enumerated.item = 3;
- strcpy(uinfo->value.enumerated.name,
- texts[uinfo->value.enumerated.item]);
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Some common info callbacks are available for your convenience:
- <function>snd_ctl_boolean_mono_info()</function> and
- <function>snd_ctl_boolean_stereo_info()</function>.
- Obviously, the former is an info callback for a mono channel
- boolean item, just like <function>snd_myctl_mono_info</function>
- above, and the latter is for a stereo channel boolean item.
- </para>
-
- </section>
-
- <section id="control-interface-callbacks-get">
- <title>get callback</title>
-
- <para>
- This callback is used to read the current value of the
- control and to return to user-space.
- </para>
-
- <para>
- For example,
-
- <example>
- <title>Example of get callback</title>
- <programlisting>
-<![CDATA[
- static int snd_myctl_get(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_value *ucontrol)
- {
- struct mychip *chip = snd_kcontrol_chip(kcontrol);
- ucontrol->value.integer.value[0] = get_some_value(chip);
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- The <structfield>value</structfield> field depends on
- the type of control as well as on the info callback. For example,
- the sb driver uses this field to store the register offset,
- the bit-shift and the bit-mask. The
- <structfield>private_value</structfield> field is set as follows:
- <informalexample>
- <programlisting>
-<![CDATA[
- .private_value = reg | (shift << 16) | (mask << 24)
-]]>
- </programlisting>
- </informalexample>
- and is retrieved in callbacks like
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_value *ucontrol)
- {
- int reg = kcontrol->private_value & 0xff;
- int shift = (kcontrol->private_value >> 16) & 0xff;
- int mask = (kcontrol->private_value >> 24) & 0xff;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In the <structfield>get</structfield> callback,
- you have to fill all the elements if the
- control has more than one elements,
- i.e. <structfield>count</structfield> &gt; 1.
- In the example above, we filled only one element
- (<structfield>value.integer.value[0]</structfield>) since it's
- assumed as <structfield>count</structfield> = 1.
- </para>
- </section>
-
- <section id="control-interface-callbacks-put">
- <title>put callback</title>
-
- <para>
- This callback is used to write a value from user-space.
- </para>
-
- <para>
- For example,
-
- <example>
- <title>Example of put callback</title>
- <programlisting>
-<![CDATA[
- static int snd_myctl_put(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_value *ucontrol)
- {
- struct mychip *chip = snd_kcontrol_chip(kcontrol);
- int changed = 0;
- if (chip->current_value !=
- ucontrol->value.integer.value[0]) {
- change_current_value(chip,
- ucontrol->value.integer.value[0]);
- changed = 1;
- }
- return changed;
- }
-]]>
- </programlisting>
- </example>
-
- As seen above, you have to return 1 if the value is
- changed. If the value is not changed, return 0 instead.
- If any fatal error happens, return a negative error code as
- usual.
- </para>
-
- <para>
- As in the <structfield>get</structfield> callback,
- when the control has more than one elements,
- all elements must be evaluated in this callback, too.
- </para>
- </section>
-
- <section id="control-interface-callbacks-all">
- <title>Callbacks are not atomic</title>
- <para>
- All these three callbacks are basically not atomic.
- </para>
- </section>
- </section>
-
- <section id="control-interface-constructor">
- <title>Constructor</title>
- <para>
- When everything is ready, finally we can create a new
- control. To create a control, there are two functions to be
- called, <function>snd_ctl_new1()</function> and
- <function>snd_ctl_add()</function>.
- </para>
-
- <para>
- In the simplest way, you can do like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip));
- if (err < 0)
- return err;
-]]>
- </programlisting>
- </informalexample>
-
- where <parameter>my_control</parameter> is the
- struct <structname>snd_kcontrol_new</structname> object defined above, and chip
- is the object pointer to be passed to
- kcontrol-&gt;private_data
- which can be referred to in callbacks.
- </para>
-
- <para>
- <function>snd_ctl_new1()</function> allocates a new
- <structname>snd_kcontrol</structname> instance (that's why the definition
- of <parameter>my_control</parameter> can be with
- the <parameter>__devinitdata</parameter>
- prefix), and <function>snd_ctl_add</function> assigns the given
- control component to the card.
- </para>
- </section>
-
- <section id="control-interface-change-notification">
- <title>Change Notification</title>
- <para>
- If you need to change and update a control in the interrupt
- routine, you can call <function>snd_ctl_notify()</function>. For
- example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer);
-]]>
- </programlisting>
- </informalexample>
-
- This function takes the card pointer, the event-mask, and the
- control id pointer for the notification. The event-mask
- specifies the types of notification, for example, in the above
- example, the change of control values is notified.
- The id pointer is the pointer of struct <structname>snd_ctl_elem_id</structname>
- to be notified.
- You can find some examples in <filename>es1938.c</filename> or
- <filename>es1968.c</filename> for hardware volume interrupts.
- </para>
- </section>
-
- <section id="control-interface-tlv">
- <title>Metadata</title>
- <para>
- To provide information about the dB values of a mixer control, use
- on of the <constant>DECLARE_TLV_xxx</constant> macros from
- <filename>&lt;sound/tlv.h&gt;</filename> to define a variable
- containing this information, set the<structfield>tlv.p
- </structfield> field to point to this variable, and include the
- <constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the
- <structfield>access</structfield> field; like this:
- <informalexample>
- <programlisting>
-<![CDATA[
- static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
-
- static struct snd_kcontrol_new my_control __devinitdata = {
- ...
- .access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
- SNDRV_CTL_ELEM_ACCESS_TLV_READ,
- ...
- .tlv.p = db_scale_my_control,
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The <function>DECLARE_TLV_DB_SCALE</function> macro defines
- information about a mixer control where each step in the control's
- value changes the dB value by a constant dB amount.
- The first parameter is the name of the variable to be defined.
- The second parameter is the minimum value, in units of 0.01 dB.
- The third parameter is the step size, in units of 0.01 dB.
- Set the fourth parameter to 1 if the minimum value actually mutes
- the control.
- </para>
-
- <para>
- The <function>DECLARE_TLV_DB_LINEAR</function> macro defines
- information about a mixer control where the control's value affects
- the output linearly.
- The first parameter is the name of the variable to be defined.
- The second parameter is the minimum value, in units of 0.01 dB.
- The third parameter is the maximum value, in units of 0.01 dB.
- If the minimum value mutes the control, set the second parameter to
- <constant>TLV_DB_GAIN_MUTE</constant>.
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- API for AC97 Codec -->
-<!-- ****************************************************** -->
- <chapter id="api-ac97">
- <title>API for AC97 Codec</title>
-
- <section>
- <title>General</title>
- <para>
- The ALSA AC97 codec layer is a well-defined one, and you don't
- have to write much code to control it. Only low-level control
- routines are necessary. The AC97 codec API is defined in
- <filename>&lt;sound/ac97_codec.h&gt;</filename>.
- </para>
- </section>
-
- <section id="api-ac97-example">
- <title>Full Code Example</title>
- <para>
- <example>
- <title>Example of AC97 Interface</title>
- <programlisting>
-<![CDATA[
- struct mychip {
- ....
- struct snd_ac97 *ac97;
- ....
- };
-
- static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
- unsigned short reg)
- {
- struct mychip *chip = ac97->private_data;
- ....
- /* read a register value here from the codec */
- return the_register_value;
- }
-
- static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
- unsigned short reg, unsigned short val)
- {
- struct mychip *chip = ac97->private_data;
- ....
- /* write the given register value to the codec */
- }
-
- static int snd_mychip_ac97(struct mychip *chip)
- {
- struct snd_ac97_bus *bus;
- struct snd_ac97_template ac97;
- int err;
- static struct snd_ac97_bus_ops ops = {
- .write = snd_mychip_ac97_write,
- .read = snd_mychip_ac97_read,
- };
-
- err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus);
- if (err < 0)
- return err;
- memset(&ac97, 0, sizeof(ac97));
- ac97.private_data = chip;
- return snd_ac97_mixer(bus, &ac97, &chip->ac97);
- }
-
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="api-ac97-constructor">
- <title>Constructor</title>
- <para>
- To create an ac97 instance, first call <function>snd_ac97_bus</function>
- with an <type>ac97_bus_ops_t</type> record with callback functions.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_ac97_bus *bus;
- static struct snd_ac97_bus_ops ops = {
- .write = snd_mychip_ac97_write,
- .read = snd_mychip_ac97_read,
- };
-
- snd_ac97_bus(card, 0, &ops, NULL, &pbus);
-]]>
- </programlisting>
- </informalexample>
-
- The bus record is shared among all belonging ac97 instances.
- </para>
-
- <para>
- And then call <function>snd_ac97_mixer()</function> with an
- struct <structname>snd_ac97_template</structname>
- record together with the bus pointer created above.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_ac97_template ac97;
- int err;
-
- memset(&ac97, 0, sizeof(ac97));
- ac97.private_data = chip;
- snd_ac97_mixer(bus, &ac97, &chip->ac97);
-]]>
- </programlisting>
- </informalexample>
-
- where chip-&gt;ac97 is a pointer to a newly created
- <type>ac97_t</type> instance.
- In this case, the chip pointer is set as the private data, so that
- the read/write callback functions can refer to this chip instance.
- This instance is not necessarily stored in the chip
- record. If you need to change the register values from the
- driver, or need the suspend/resume of ac97 codecs, keep this
- pointer to pass to the corresponding functions.
- </para>
- </section>
-
- <section id="api-ac97-callbacks">
- <title>Callbacks</title>
- <para>
- The standard callbacks are <structfield>read</structfield> and
- <structfield>write</structfield>. Obviously they
- correspond to the functions for read and write accesses to the
- hardware low-level codes.
- </para>
-
- <para>
- The <structfield>read</structfield> callback returns the
- register value specified in the argument.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
- unsigned short reg)
- {
- struct mychip *chip = ac97->private_data;
- ....
- return the_register_value;
- }
-]]>
- </programlisting>
- </informalexample>
-
- Here, the chip can be cast from ac97-&gt;private_data.
- </para>
-
- <para>
- Meanwhile, the <structfield>write</structfield> callback is
- used to set the register value.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
- unsigned short reg, unsigned short val)
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- These callbacks are non-atomic like the control API callbacks.
- </para>
-
- <para>
- There are also other callbacks:
- <structfield>reset</structfield>,
- <structfield>wait</structfield> and
- <structfield>init</structfield>.
- </para>
-
- <para>
- The <structfield>reset</structfield> callback is used to reset
- the codec. If the chip requires a special kind of reset, you can
- define this callback.
- </para>
-
- <para>
- The <structfield>wait</structfield> callback is used to
- add some waiting time in the standard initialization of the codec. If the
- chip requires the extra waiting time, define this callback.
- </para>
-
- <para>
- The <structfield>init</structfield> callback is used for
- additional initialization of the codec.
- </para>
- </section>
-
- <section id="api-ac97-updating-registers">
- <title>Updating Registers in The Driver</title>
- <para>
- If you need to access to the codec from the driver, you can
- call the following functions:
- <function>snd_ac97_write()</function>,
- <function>snd_ac97_read()</function>,
- <function>snd_ac97_update()</function> and
- <function>snd_ac97_update_bits()</function>.
- </para>
-
- <para>
- Both <function>snd_ac97_write()</function> and
- <function>snd_ac97_update()</function> functions are used to
- set a value to the given register
- (<constant>AC97_XXX</constant>). The difference between them is
- that <function>snd_ac97_update()</function> doesn't write a
- value if the given value has been already set, while
- <function>snd_ac97_write()</function> always rewrites the
- value.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ac97_write(ac97, AC97_MASTER, 0x8080);
- snd_ac97_update(ac97, AC97_MASTER, 0x8080);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <function>snd_ac97_read()</function> is used to read the value
- of the given register. For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- value = snd_ac97_read(ac97, AC97_MASTER);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <function>snd_ac97_update_bits()</function> is used to update
- some bits in the given register.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ac97_update_bits(ac97, reg, mask, value);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Also, there is a function to change the sample rate (of a
- given register such as
- <constant>AC97_PCM_FRONT_DAC_RATE</constant>) when VRA or
- DRA is supported by the codec:
- <function>snd_ac97_set_rate()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The following registers are available to set the rate:
- <constant>AC97_PCM_MIC_ADC_RATE</constant>,
- <constant>AC97_PCM_FRONT_DAC_RATE</constant>,
- <constant>AC97_PCM_LR_ADC_RATE</constant>,
- <constant>AC97_SPDIF</constant>. When
- <constant>AC97_SPDIF</constant> is specified, the register is
- not really changed but the corresponding IEC958 status bits will
- be updated.
- </para>
- </section>
-
- <section id="api-ac97-clock-adjustment">
- <title>Clock Adjustment</title>
- <para>
- In some chips, the clock of the codec isn't 48000 but using a
- PCI clock (to save a quartz!). In this case, change the field
- bus-&gt;clock to the corresponding
- value. For example, intel8x0
- and es1968 drivers have their own function to read from the clock.
- </para>
- </section>
-
- <section id="api-ac97-proc-files">
- <title>Proc Files</title>
- <para>
- The ALSA AC97 interface will create a proc file such as
- <filename>/proc/asound/card0/codec97#0/ac97#0-0</filename> and
- <filename>ac97#0-0+regs</filename>. You can refer to these files to
- see the current status and registers of the codec.
- </para>
- </section>
-
- <section id="api-ac97-multiple-codecs">
- <title>Multiple Codecs</title>
- <para>
- When there are several codecs on the same card, you need to
- call <function>snd_ac97_mixer()</function> multiple times with
- ac97.num=1 or greater. The <structfield>num</structfield> field
- specifies the codec number.
- </para>
-
- <para>
- If you set up multiple codecs, you either need to write
- different callbacks for each codec or check
- ac97-&gt;num in the callback routines.
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- MIDI (MPU401-UART) Interface -->
-<!-- ****************************************************** -->
- <chapter id="midi-interface">
- <title>MIDI (MPU401-UART) Interface</title>
-
- <section id="midi-interface-general">
- <title>General</title>
- <para>
- Many soundcards have built-in MIDI (MPU401-UART)
- interfaces. When the soundcard supports the standard MPU401-UART
- interface, most likely you can use the ALSA MPU401-UART API. The
- MPU401-UART API is defined in
- <filename>&lt;sound/mpu401.h&gt;</filename>.
- </para>
-
- <para>
- Some soundchips have a similar but slightly different
- implementation of mpu401 stuff. For example, emu10k1 has its own
- mpu401 routines.
- </para>
- </section>
-
- <section id="midi-interface-constructor">
- <title>Constructor</title>
- <para>
- To create a rawmidi object, call
- <function>snd_mpu401_uart_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi *rmidi;
- snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags,
- irq, &rmidi);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the card pointer, and the second is the
- index of this component. You can create up to 8 rawmidi
- devices.
- </para>
-
- <para>
- The third argument is the type of the hardware,
- <constant>MPU401_HW_XXX</constant>. If it's not a special one,
- you can use <constant>MPU401_HW_MPU401</constant>.
- </para>
-
- <para>
- The 4th argument is the I/O port address. Many
- backward-compatible MPU401 have an I/O port such as 0x330. Or, it
- might be a part of its own PCI I/O region. It depends on the
- chip design.
- </para>
-
- <para>
- The 5th argument is a bitflag for additional information.
- When the I/O port address above is part of the PCI I/O
- region, the MPU401 I/O port might have been already allocated
- (reserved) by the driver itself. In such a case, pass a bit flag
- <constant>MPU401_INFO_INTEGRATED</constant>,
- and the mpu401-uart layer will allocate the I/O ports by itself.
- </para>
-
- <para>
- When the controller supports only the input or output MIDI stream,
- pass the <constant>MPU401_INFO_INPUT</constant> or
- <constant>MPU401_INFO_OUTPUT</constant> bitflag, respectively.
- Then the rawmidi instance is created as a single stream.
- </para>
-
- <para>
- <constant>MPU401_INFO_MMIO</constant> bitflag is used to change
- the access method to MMIO (via readb and writeb) instead of
- iob and outb. In this case, you have to pass the iomapped address
- to <function>snd_mpu401_uart_new()</function>.
- </para>
-
- <para>
- When <constant>MPU401_INFO_TX_IRQ</constant> is set, the output
- stream isn't checked in the default interrupt handler. The driver
- needs to call <function>snd_mpu401_uart_interrupt_tx()</function>
- by itself to start processing the output stream in the irq handler.
- </para>
-
- <para>
- If the MPU-401 interface shares its interrupt with the other logical
- devices on the card, set <constant>MPU401_INFO_IRQ_HOOK</constant>
- (see <link linkend="midi-interface-interrupt-handler"><citetitle>
- below</citetitle></link>).
- </para>
-
- <para>
- Usually, the port address corresponds to the command port and
- port + 1 corresponds to the data port. If not, you may change
- the <structfield>cport</structfield> field of
- struct <structname>snd_mpu401</structname> manually
- afterward. However, <structname>snd_mpu401</structname> pointer is not
- returned explicitly by
- <function>snd_mpu401_uart_new()</function>. You need to cast
- rmidi-&gt;private_data to
- <structname>snd_mpu401</structname> explicitly,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_mpu401 *mpu;
- mpu = rmidi->private_data;
-]]>
- </programlisting>
- </informalexample>
-
- and reset the cport as you like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- mpu->cport = my_own_control_port;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The 6th argument specifies the ISA irq number that will be
- allocated. If no interrupt is to be allocated (because your
- code is already allocating a shared interrupt, or because the
- device does not use interrupts), pass -1 instead.
- For a MPU-401 device without an interrupt, a polling timer
- will be used instead.
- </para>
- </section>
-
- <section id="midi-interface-interrupt-handler">
- <title>Interrupt Handler</title>
- <para>
- When the interrupt is allocated in
- <function>snd_mpu401_uart_new()</function>, an exclusive ISA
- interrupt handler is automatically used, hence you don't have
- anything else to do than creating the mpu401 stuff. Otherwise, you
- have to set <constant>MPU401_INFO_IRQ_HOOK</constant>, and call
- <function>snd_mpu401_uart_interrupt()</function> explicitly from your
- own interrupt handler when it has determined that a UART interrupt
- has occurred.
- </para>
-
- <para>
- In this case, you need to pass the private_data of the
- returned rawmidi object from
- <function>snd_mpu401_uart_new()</function> as the second
- argument of <function>snd_mpu401_uart_interrupt()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs);
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- RawMIDI Interface -->
-<!-- ****************************************************** -->
- <chapter id="rawmidi-interface">
- <title>RawMIDI Interface</title>
-
- <section id="rawmidi-interface-overview">
- <title>Overview</title>
-
- <para>
- The raw MIDI interface is used for hardware MIDI ports that can
- be accessed as a byte stream. It is not used for synthesizer
- chips that do not directly understand MIDI.
- </para>
-
- <para>
- ALSA handles file and buffer management. All you have to do is
- to write some code to move data between the buffer and the
- hardware.
- </para>
-
- <para>
- The rawmidi API is defined in
- <filename>&lt;sound/rawmidi.h&gt;</filename>.
- </para>
- </section>
-
- <section id="rawmidi-interface-constructor">
- <title>Constructor</title>
-
- <para>
- To create a rawmidi device, call the
- <function>snd_rawmidi_new</function> function:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi *rmidi;
- err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi);
- if (err < 0)
- return err;
- rmidi->private_data = chip;
- strcpy(rmidi->name, "My MIDI");
- rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
- SNDRV_RAWMIDI_INFO_INPUT |
- SNDRV_RAWMIDI_INFO_DUPLEX;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the card pointer, the second argument is
- the ID string.
- </para>
-
- <para>
- The third argument is the index of this component. You can
- create up to 8 rawmidi devices.
- </para>
-
- <para>
- The fourth and fifth arguments are the number of output and
- input substreams, respectively, of this device (a substream is
- the equivalent of a MIDI port).
- </para>
-
- <para>
- Set the <structfield>info_flags</structfield> field to specify
- the capabilities of the device.
- Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is
- at least one output port,
- <constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at
- least one input port,
- and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device
- can handle output and input at the same time.
- </para>
-
- <para>
- After the rawmidi device is created, you need to set the
- operators (callbacks) for each substream. There are helper
- functions to set the operators for all the substreams of a device:
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops);
- snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The operators are usually defined like this:
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_rawmidi_ops snd_mymidi_output_ops = {
- .open = snd_mymidi_output_open,
- .close = snd_mymidi_output_close,
- .trigger = snd_mymidi_output_trigger,
- };
-]]>
- </programlisting>
- </informalexample>
- These callbacks are explained in the <link
- linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link>
- section.
- </para>
-
- <para>
- If there are more than one substream, you should give a
- unique name to each of them:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi_substream *substream;
- list_for_each_entry(substream,
- &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams,
- list {
- sprintf(substream->name, "My MIDI Port %d", substream->number + 1);
- }
- /* same for SNDRV_RAWMIDI_STREAM_INPUT */
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="rawmidi-interface-callbacks">
- <title>Callbacks</title>
-
- <para>
- In all the callbacks, the private data that you've set for the
- rawmidi device can be accessed as
- substream-&gt;rmidi-&gt;private_data.
- <!-- <code> isn't available before DocBook 4.3 -->
- </para>
-
- <para>
- If there is more than one port, your callbacks can determine the
- port index from the struct snd_rawmidi_substream data passed to each
- callback:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi_substream *substream;
- int index = substream->number;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <section id="rawmidi-interface-op-open">
- <title><function>open</function> callback</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_rawmidi_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is called when a substream is opened.
- You can initialize the hardware here, but you shouldn't
- start transmitting/receiving data yet.
- </para>
- </section>
-
- <section id="rawmidi-interface-op-close">
- <title><function>close</function> callback</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_close(struct snd_rawmidi_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- Guess what.
- </para>
-
- <para>
- The <function>open</function> and <function>close</function>
- callbacks of a rawmidi device are serialized with a mutex,
- and can sleep.
- </para>
- </section>
-
- <section id="rawmidi-interface-op-trigger-out">
- <title><function>trigger</function> callback for output
- substreams</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is called with a nonzero <parameter>up</parameter>
- parameter when there is some data in the substream buffer that
- must be transmitted.
- </para>
-
- <para>
- To read data from the buffer, call
- <function>snd_rawmidi_transmit_peek</function>. It will
- return the number of bytes that have been read; this will be
- less than the number of bytes requested when there are no more
- data in the buffer.
- After the data have been transmitted successfully, call
- <function>snd_rawmidi_transmit_ack</function> to remove the
- data from the substream buffer:
- <informalexample>
- <programlisting>
-<![CDATA[
- unsigned char data;
- while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) {
- if (snd_mychip_try_to_transmit(data))
- snd_rawmidi_transmit_ack(substream, 1);
- else
- break; /* hardware FIFO full */
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- If you know beforehand that the hardware will accept data, you
- can use the <function>snd_rawmidi_transmit</function> function
- which reads some data and removes them from the buffer at once:
- <informalexample>
- <programlisting>
-<![CDATA[
- while (snd_mychip_transmit_possible()) {
- unsigned char data;
- if (snd_rawmidi_transmit(substream, &data, 1) != 1)
- break; /* no more data */
- snd_mychip_transmit(data);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- If you know beforehand how many bytes you can accept, you can
- use a buffer size greater than one with the
- <function>snd_rawmidi_transmit*</function> functions.
- </para>
-
- <para>
- The <function>trigger</function> callback must not sleep. If
- the hardware FIFO is full before the substream buffer has been
- emptied, you have to continue transmitting data later, either
- in an interrupt handler, or with a timer if the hardware
- doesn't have a MIDI transmit interrupt.
- </para>
-
- <para>
- The <function>trigger</function> callback is called with a
- zero <parameter>up</parameter> parameter when the transmission
- of data should be aborted.
- </para>
- </section>
-
- <section id="rawmidi-interface-op-trigger-in">
- <title><function>trigger</function> callback for input
- substreams</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is called with a nonzero <parameter>up</parameter>
- parameter to enable receiving data, or with a zero
- <parameter>up</parameter> parameter do disable receiving data.
- </para>
-
- <para>
- The <function>trigger</function> callback must not sleep; the
- actual reading of data from the device is usually done in an
- interrupt handler.
- </para>
-
- <para>
- When data reception is enabled, your interrupt handler should
- call <function>snd_rawmidi_receive</function> for all received
- data:
- <informalexample>
- <programlisting>
-<![CDATA[
- void snd_mychip_midi_interrupt(...)
- {
- while (mychip_midi_available()) {
- unsigned char data;
- data = mychip_midi_read();
- snd_rawmidi_receive(substream, &data, 1);
- }
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="rawmidi-interface-op-drain">
- <title><function>drain</function> callback</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_xxx_drain(struct snd_rawmidi_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is only used with output substreams. This function should wait
- until all data read from the substream buffer have been transmitted.
- This ensures that the device can be closed and the driver unloaded
- without losing data.
- </para>
-
- <para>
- This callback is optional. If you do not set
- <structfield>drain</structfield> in the struct snd_rawmidi_ops
- structure, ALSA will simply wait for 50&nbsp;milliseconds
- instead.
- </para>
- </section>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Miscellaneous Devices -->
-<!-- ****************************************************** -->
- <chapter id="misc-devices">
- <title>Miscellaneous Devices</title>
-
- <section id="misc-devices-opl3">
- <title>FM OPL3</title>
- <para>
- The FM OPL3 is still used in many chips (mainly for backward
- compatibility). ALSA has a nice OPL3 FM control layer, too. The
- OPL3 API is defined in
- <filename>&lt;sound/opl3.h&gt;</filename>.
- </para>
-
- <para>
- FM registers can be directly accessed through the direct-FM API,
- defined in <filename>&lt;sound/asound_fm.h&gt;</filename>. In
- ALSA native mode, FM registers are accessed through
- the Hardware-Dependent Device direct-FM extension API, whereas in
- OSS compatible mode, FM registers can be accessed with the OSS
- direct-FM compatible API in <filename>/dev/dmfmX</filename> device.
- </para>
-
- <para>
- To create the OPL3 component, you have two functions to
- call. The first one is a constructor for the <type>opl3_t</type>
- instance.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_opl3 *opl3;
- snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX,
- integrated, &opl3);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the card pointer, the second one is the
- left port address, and the third is the right port address. In
- most cases, the right port is placed at the left port + 2.
- </para>
-
- <para>
- The fourth argument is the hardware type.
- </para>
-
- <para>
- When the left and right ports have been already allocated by
- the card driver, pass non-zero to the fifth argument
- (<parameter>integrated</parameter>). Otherwise, the opl3 module will
- allocate the specified ports by itself.
- </para>
-
- <para>
- When the accessing the hardware requires special method
- instead of the standard I/O access, you can create opl3 instance
- separately with <function>snd_opl3_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_opl3 *opl3;
- snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Then set <structfield>command</structfield>,
- <structfield>private_data</structfield> and
- <structfield>private_free</structfield> for the private
- access function, the private data and the destructor.
- The l_port and r_port are not necessarily set. Only the
- command must be set properly. You can retrieve the data
- from the opl3-&gt;private_data field.
- </para>
-
- <para>
- After creating the opl3 instance via <function>snd_opl3_new()</function>,
- call <function>snd_opl3_init()</function> to initialize the chip to the
- proper state. Note that <function>snd_opl3_create()</function> always
- calls it internally.
- </para>
-
- <para>
- If the opl3 instance is created successfully, then create a
- hwdep device for this opl3.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_hwdep *opl3hwdep;
- snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the <type>opl3_t</type> instance you
- created, and the second is the index number, usually 0.
- </para>
-
- <para>
- The third argument is the index-offset for the sequencer
- client assigned to the OPL3 port. When there is an MPU401-UART,
- give 1 for here (UART always takes 0).
- </para>
- </section>
-
- <section id="misc-devices-hardware-dependent">
- <title>Hardware-Dependent Devices</title>
- <para>
- Some chips need user-space access for special
- controls or for loading the micro code. In such a case, you can
- create a hwdep (hardware-dependent) device. The hwdep API is
- defined in <filename>&lt;sound/hwdep.h&gt;</filename>. You can
- find examples in opl3 driver or
- <filename>isa/sb/sb16_csp.c</filename>.
- </para>
-
- <para>
- The creation of the <type>hwdep</type> instance is done via
- <function>snd_hwdep_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_hwdep *hw;
- snd_hwdep_new(card, "My HWDEP", 0, &hw);
-]]>
- </programlisting>
- </informalexample>
-
- where the third argument is the index number.
- </para>
-
- <para>
- You can then pass any pointer value to the
- <parameter>private_data</parameter>.
- If you assign a private data, you should define the
- destructor, too. The destructor function is set in
- the <structfield>private_free</structfield> field.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL);
- hw->private_data = p;
- hw->private_free = mydata_free;
-]]>
- </programlisting>
- </informalexample>
-
- and the implementation of the destructor would be:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void mydata_free(struct snd_hwdep *hw)
- {
- struct mydata *p = hw->private_data;
- kfree(p);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The arbitrary file operations can be defined for this
- instance. The file operators are defined in
- the <parameter>ops</parameter> table. For example, assume that
- this chip needs an ioctl.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- hw->ops.open = mydata_open;
- hw->ops.ioctl = mydata_ioctl;
- hw->ops.release = mydata_release;
-]]>
- </programlisting>
- </informalexample>
-
- And implement the callback functions as you like.
- </para>
- </section>
-
- <section id="misc-devices-IEC958">
- <title>IEC958 (S/PDIF)</title>
- <para>
- Usually the controls for IEC958 devices are implemented via
- the control interface. There is a macro to compose a name string for
- IEC958 controls, <function>SNDRV_CTL_NAME_IEC958()</function>
- defined in <filename>&lt;include/asound.h&gt;</filename>.
- </para>
-
- <para>
- There are some standard controls for IEC958 status bits. These
- controls use the type <type>SNDRV_CTL_ELEM_TYPE_IEC958</type>,
- and the size of element is fixed as 4 bytes array
- (value.iec958.status[x]). For the <structfield>info</structfield>
- callback, you don't specify
- the value field for this type (the count field must be set,
- though).
- </para>
-
- <para>
- <quote>IEC958 Playback Con Mask</quote> is used to return the
- bit-mask for the IEC958 status bits of consumer mode. Similarly,
- <quote>IEC958 Playback Pro Mask</quote> returns the bitmask for
- professional mode. They are read-only controls, and are defined
- as MIXER controls (iface =
- <constant>SNDRV_CTL_ELEM_IFACE_MIXER</constant>).
- </para>
-
- <para>
- Meanwhile, <quote>IEC958 Playback Default</quote> control is
- defined for getting and setting the current default IEC958
- bits. Note that this one is usually defined as a PCM control
- (iface = <constant>SNDRV_CTL_ELEM_IFACE_PCM</constant>),
- although in some places it's defined as a MIXER control.
- </para>
-
- <para>
- In addition, you can define the control switches to
- enable/disable or to set the raw bit mode. The implementation
- will depend on the chip, but the control should be named as
- <quote>IEC958 xxx</quote>, preferably using
- the <function>SNDRV_CTL_NAME_IEC958()</function> macro.
- </para>
-
- <para>
- You can find several cases, for example,
- <filename>pci/emu10k1</filename>,
- <filename>pci/ice1712</filename>, or
- <filename>pci/cmipci.c</filename>.
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Buffer and Memory Management -->
-<!-- ****************************************************** -->
- <chapter id="buffer-and-memory">
- <title>Buffer and Memory Management</title>
-
- <section id="buffer-and-memory-buffer-types">
- <title>Buffer Types</title>
- <para>
- ALSA provides several different buffer allocation functions
- depending on the bus and the architecture. All these have a
- consistent API. The allocation of physically-contiguous pages is
- done via
- <function>snd_malloc_xxx_pages()</function> function, where xxx
- is the bus type.
- </para>
-
- <para>
- The allocation of pages with fallback is
- <function>snd_malloc_xxx_pages_fallback()</function>. This
- function tries to allocate the specified pages but if the pages
- are not available, it tries to reduce the page sizes until
- enough space is found.
- </para>
-
- <para>
- The release the pages, call
- <function>snd_free_xxx_pages()</function> function.
- </para>
-
- <para>
- Usually, ALSA drivers try to allocate and reserve
- a large contiguous physical space
- at the time the module is loaded for the later use.
- This is called <quote>pre-allocation</quote>.
- As already written, you can call the following function at
- pcm instance construction time (in the case of PCI bus).
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
- snd_dma_pci_data(pci), size, max);
-]]>
- </programlisting>
- </informalexample>
-
- where <parameter>size</parameter> is the byte size to be
- pre-allocated and the <parameter>max</parameter> is the maximum
- size to be changed via the <filename>prealloc</filename> proc file.
- The allocator will try to get an area as large as possible
- within the given size.
- </para>
-
- <para>
- The second argument (type) and the third argument (device pointer)
- are dependent on the bus.
- In the case of the ISA bus, pass <function>snd_dma_isa_data()</function>
- as the third argument with <constant>SNDRV_DMA_TYPE_DEV</constant> type.
- For the continuous buffer unrelated to the bus can be pre-allocated
- with <constant>SNDRV_DMA_TYPE_CONTINUOUS</constant> type and the
- <function>snd_dma_continuous_data(GFP_KERNEL)</function> device pointer,
- where <constant>GFP_KERNEL</constant> is the kernel allocation flag to
- use.
- For the PCI scatter-gather buffers, use
- <constant>SNDRV_DMA_TYPE_DEV_SG</constant> with
- <function>snd_dma_pci_data(pci)</function>
- (see the
- <link linkend="buffer-and-memory-non-contiguous"><citetitle>Non-Contiguous Buffers
- </citetitle></link> section).
- </para>
-
- <para>
- Once the buffer is pre-allocated, you can use the
- allocator in the <structfield>hw_params</structfield> callback:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_malloc_pages(substream, size);
-]]>
- </programlisting>
- </informalexample>
-
- Note that you have to pre-allocate to use this function.
- </para>
- </section>
-
- <section id="buffer-and-memory-external-hardware">
- <title>External Hardware Buffers</title>
- <para>
- Some chips have their own hardware buffers and the DMA
- transfer from the host memory is not available. In such a case,
- you need to either 1) copy/set the audio data directly to the
- external hardware buffer, or 2) make an intermediate buffer and
- copy/set the data from it to the external hardware buffer in
- interrupts (or in tasklets, preferably).
- </para>
-
- <para>
- The first case works fine if the external hardware buffer is large
- enough. This method doesn't need any extra buffers and thus is
- more effective. You need to define the
- <structfield>copy</structfield> and
- <structfield>silence</structfield> callbacks for
- the data transfer. However, there is a drawback: it cannot
- be mmapped. The examples are GUS's GF1 PCM or emu8000's
- wavetable PCM.
- </para>
-
- <para>
- The second case allows for mmap on the buffer, although you have
- to handle an interrupt or a tasklet to transfer the data
- from the intermediate buffer to the hardware buffer. You can find an
- example in the vxpocket driver.
- </para>
-
- <para>
- Another case is when the chip uses a PCI memory-map
- region for the buffer instead of the host memory. In this case,
- mmap is available only on certain architectures like the Intel one.
- In non-mmap mode, the data cannot be transferred as in the normal
- way. Thus you need to define the <structfield>copy</structfield> and
- <structfield>silence</structfield> callbacks as well,
- as in the cases above. The examples are found in
- <filename>rme32.c</filename> and <filename>rme96.c</filename>.
- </para>
-
- <para>
- The implementation of the <structfield>copy</structfield> and
- <structfield>silence</structfield> callbacks depends upon
- whether the hardware supports interleaved or non-interleaved
- samples. The <structfield>copy</structfield> callback is
- defined like below, a bit
- differently depending whether the direction is playback or
- capture:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int playback_copy(struct snd_pcm_substream *substream, int channel,
- snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count);
- static int capture_copy(struct snd_pcm_substream *substream, int channel,
- snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In the case of interleaved samples, the second argument
- (<parameter>channel</parameter>) is not used. The third argument
- (<parameter>pos</parameter>) points the
- current position offset in frames.
- </para>
-
- <para>
- The meaning of the fourth argument is different between
- playback and capture. For playback, it holds the source data
- pointer, and for capture, it's the destination data pointer.
- </para>
-
- <para>
- The last argument is the number of frames to be copied.
- </para>
-
- <para>
- What you have to do in this callback is again different
- between playback and capture directions. In the
- playback case, you copy the given amount of data
- (<parameter>count</parameter>) at the specified pointer
- (<parameter>src</parameter>) to the specified offset
- (<parameter>pos</parameter>) on the hardware buffer. When
- coded like memcpy-like way, the copy would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src,
- frames_to_bytes(runtime, count));
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For the capture direction, you copy the given amount of
- data (<parameter>count</parameter>) at the specified offset
- (<parameter>pos</parameter>) on the hardware buffer to the
- specified pointer (<parameter>dst</parameter>).
-
- <informalexample>
- <programlisting>
-<![CDATA[
- my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos),
- frames_to_bytes(runtime, count));
-]]>
- </programlisting>
- </informalexample>
-
- Note that both the position and the amount of data are given
- in frames.
- </para>
-
- <para>
- In the case of non-interleaved samples, the implementation
- will be a bit more complicated.
- </para>
-
- <para>
- You need to check the channel argument, and if it's -1, copy
- the whole channels. Otherwise, you have to copy only the
- specified channel. Please check
- <filename>isa/gus/gus_pcm.c</filename> as an example.
- </para>
-
- <para>
- The <structfield>silence</structfield> callback is also
- implemented in a similar way.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int silence(struct snd_pcm_substream *substream, int channel,
- snd_pcm_uframes_t pos, snd_pcm_uframes_t count);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The meanings of arguments are the same as in the
- <structfield>copy</structfield>
- callback, although there is no <parameter>src/dst</parameter>
- argument. In the case of interleaved samples, the channel
- argument has no meaning, as well as on
- <structfield>copy</structfield> callback.
- </para>
-
- <para>
- The role of <structfield>silence</structfield> callback is to
- set the given amount
- (<parameter>count</parameter>) of silence data at the
- specified offset (<parameter>pos</parameter>) on the hardware
- buffer. Suppose that the data format is signed (that is, the
- silent-data is 0), and the implementation using a memset-like
- function would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0,
- frames_to_bytes(runtime, count));
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In the case of non-interleaved samples, again, the
- implementation becomes a bit more complicated. See, for example,
- <filename>isa/gus/gus_pcm.c</filename>.
- </para>
- </section>
-
- <section id="buffer-and-memory-non-contiguous">
- <title>Non-Contiguous Buffers</title>
- <para>
- If your hardware supports the page table as in emu10k1 or the
- buffer descriptors as in via82xx, you can use the scatter-gather
- (SG) DMA. ALSA provides an interface for handling SG-buffers.
- The API is provided in <filename>&lt;sound/pcm.h&gt;</filename>.
- </para>
-
- <para>
- For creating the SG-buffer handler, call
- <function>snd_pcm_lib_preallocate_pages()</function> or
- <function>snd_pcm_lib_preallocate_pages_for_all()</function>
- with <constant>SNDRV_DMA_TYPE_DEV_SG</constant>
- in the PCM constructor like other PCI pre-allocator.
- You need to pass <function>snd_dma_pci_data(pci)</function>,
- where pci is the struct <structname>pci_dev</structname> pointer
- of the chip as well.
- The <type>struct snd_sg_buf</type> instance is created as
- substream-&gt;dma_private. You can cast
- the pointer like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Then call <function>snd_pcm_lib_malloc_pages()</function>
- in the <structfield>hw_params</structfield> callback
- as well as in the case of normal PCI buffer.
- The SG-buffer handler will allocate the non-contiguous kernel
- pages of the given size and map them onto the virtually contiguous
- memory. The virtual pointer is addressed in runtime-&gt;dma_area.
- The physical address (runtime-&gt;dma_addr) is set to zero,
- because the buffer is physically non-contiguous.
- The physical address table is set up in sgbuf-&gt;table.
- You can get the physical address at a certain offset via
- <function>snd_pcm_sgbuf_get_addr()</function>.
- </para>
-
- <para>
- When a SG-handler is used, you need to set
- <function>snd_pcm_sgbuf_ops_page</function> as
- the <structfield>page</structfield> callback.
- (See <link linkend="pcm-interface-operators-page-callback">
- <citetitle>page callback section</citetitle></link>.)
- </para>
-
- <para>
- To release the data, call
- <function>snd_pcm_lib_free_pages()</function> in the
- <structfield>hw_free</structfield> callback as usual.
- </para>
- </section>
-
- <section id="buffer-and-memory-vmalloced">
- <title>Vmalloc'ed Buffers</title>
- <para>
- It's possible to use a buffer allocated via
- <function>vmalloc</function>, for example, for an intermediate
- buffer. Since the allocated pages are not contiguous, you need
- to set the <structfield>page</structfield> callback to obtain
- the physical address at every offset.
- </para>
-
- <para>
- The implementation of <structfield>page</structfield> callback
- would be like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #include <linux/vmalloc.h>
-
- /* get the physical page pointer on the given offset */
- static struct page *mychip_page(struct snd_pcm_substream *substream,
- unsigned long offset)
- {
- void *pageptr = substream->runtime->dma_area + offset;
- return vmalloc_to_page(pageptr);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Proc Interface -->
-<!-- ****************************************************** -->
- <chapter id="proc-interface">
- <title>Proc Interface</title>
- <para>
- ALSA provides an easy interface for procfs. The proc files are
- very useful for debugging. I recommend you set up proc files if
- you write a driver and want to get a running status or register
- dumps. The API is found in
- <filename>&lt;sound/info.h&gt;</filename>.
- </para>
-
- <para>
- To create a proc file, call
- <function>snd_card_proc_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_info_entry *entry;
- int err = snd_card_proc_new(card, "my-file", &entry);
-]]>
- </programlisting>
- </informalexample>
-
- where the second argument specifies the name of the proc file to be
- created. The above example will create a file
- <filename>my-file</filename> under the card directory,
- e.g. <filename>/proc/asound/card0/my-file</filename>.
- </para>
-
- <para>
- Like other components, the proc entry created via
- <function>snd_card_proc_new()</function> will be registered and
- released automatically in the card registration and release
- functions.
- </para>
-
- <para>
- When the creation is successful, the function stores a new
- instance in the pointer given in the third argument.
- It is initialized as a text proc file for read only. To use
- this proc file as a read-only text file as it is, set the read
- callback with a private data via
- <function>snd_info_set_text_ops()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_info_set_text_ops(entry, chip, my_proc_read);
-]]>
- </programlisting>
- </informalexample>
-
- where the second argument (<parameter>chip</parameter>) is the
- private data to be used in the callbacks. The third parameter
- specifies the read buffer size and the fourth
- (<parameter>my_proc_read</parameter>) is the callback function, which
- is defined like
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void my_proc_read(struct snd_info_entry *entry,
- struct snd_info_buffer *buffer);
-]]>
- </programlisting>
- </informalexample>
-
- </para>
-
- <para>
- In the read callback, use <function>snd_iprintf()</function> for
- output strings, which works just like normal
- <function>printf()</function>. For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void my_proc_read(struct snd_info_entry *entry,
- struct snd_info_buffer *buffer)
- {
- struct my_chip *chip = entry->private_data;
-
- snd_iprintf(buffer, "This is my chip!\n");
- snd_iprintf(buffer, "Port = %ld\n", chip->port);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The file permissions can be changed afterwards. As default, it's
- set as read only for all users. If you want to add write
- permission for the user (root as default), do as follows:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- entry->mode = S_IFREG | S_IRUGO | S_IWUSR;
-]]>
- </programlisting>
- </informalexample>
-
- and set the write buffer size and the callback
-
- <informalexample>
- <programlisting>
-<![CDATA[
- entry->c.text.write = my_proc_write;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For the write callback, you can use
- <function>snd_info_get_line()</function> to get a text line, and
- <function>snd_info_get_str()</function> to retrieve a string from
- the line. Some examples are found in
- <filename>core/oss/mixer_oss.c</filename>, core/oss/and
- <filename>pcm_oss.c</filename>.
- </para>
-
- <para>
- For a raw-data proc-file, set the attributes as follows:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_info_entry_ops my_file_io_ops = {
- .read = my_file_io_read,
- };
-
- entry->content = SNDRV_INFO_CONTENT_DATA;
- entry->private_data = chip;
- entry->c.ops = &my_file_io_ops;
- entry->size = 4096;
- entry->mode = S_IFREG | S_IRUGO;
-]]>
- </programlisting>
- </informalexample>
-
- For the raw data, <structfield>size</structfield> field must be
- set properly. This specifies the maximum size of the proc file access.
- </para>
-
- <para>
- The read/write callbacks of raw mode are more direct than the text mode.
- You need to use a low-level I/O functions such as
- <function>copy_from/to_user()</function> to transfer the
- data.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static ssize_t my_file_io_read(struct snd_info_entry *entry,
- void *file_private_data,
- struct file *file,
- char *buf,
- size_t count,
- loff_t pos)
- {
- if (copy_to_user(buf, local_data + pos, count))
- return -EFAULT;
- return count;
- }
-]]>
- </programlisting>
- </informalexample>
-
- If the size of the info entry has been set up properly,
- <structfield>count</structfield> and <structfield>pos</structfield> are
- guaranteed to fit within 0 and the given size.
- You don't have to check the range in the callbacks unless any
- other condition is required.
-
- </para>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Power Management -->
-<!-- ****************************************************** -->
- <chapter id="power-management">
- <title>Power Management</title>
- <para>
- If the chip is supposed to work with suspend/resume
- functions, you need to add power-management code to the
- driver. The additional code for power-management should be
- <function>ifdef</function>'ed with
- <constant>CONFIG_PM</constant>.
- </para>
-
- <para>
- If the driver <emphasis>fully</emphasis> supports suspend/resume
- that is, the device can be
- properly resumed to its state when suspend was called,
- you can set the <constant>SNDRV_PCM_INFO_RESUME</constant> flag
- in the pcm info field. Usually, this is possible when the
- registers of the chip can be safely saved and restored to
- RAM. If this is set, the trigger callback is called with
- <constant>SNDRV_PCM_TRIGGER_RESUME</constant> after the resume
- callback completes.
- </para>
-
- <para>
- Even if the driver doesn't support PM fully but
- partial suspend/resume is still possible, it's still worthy to
- implement suspend/resume callbacks. In such a case, applications
- would reset the status by calling
- <function>snd_pcm_prepare()</function> and restart the stream
- appropriately. Hence, you can define suspend/resume callbacks
- below but don't set <constant>SNDRV_PCM_INFO_RESUME</constant>
- info flag to the PCM.
- </para>
-
- <para>
- Note that the trigger with SUSPEND can always be called when
- <function>snd_pcm_suspend_all</function> is called,
- regardless of the <constant>SNDRV_PCM_INFO_RESUME</constant> flag.
- The <constant>RESUME</constant> flag affects only the behavior
- of <function>snd_pcm_resume()</function>.
- (Thus, in theory,
- <constant>SNDRV_PCM_TRIGGER_RESUME</constant> isn't needed
- to be handled in the trigger callback when no
- <constant>SNDRV_PCM_INFO_RESUME</constant> flag is set. But,
- it's better to keep it for compatibility reasons.)
- </para>
- <para>
- In the earlier version of ALSA drivers, a common
- power-management layer was provided, but it has been removed.
- The driver needs to define the suspend/resume hooks according to
- the bus the device is connected to. In the case of PCI drivers, the
- callbacks look like below:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #ifdef CONFIG_PM
- static int snd_my_suspend(struct pci_dev *pci, pm_message_t state)
- {
- .... /* do things for suspend */
- return 0;
- }
- static int snd_my_resume(struct pci_dev *pci)
- {
- .... /* do things for suspend */
- return 0;
- }
- #endif
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The scheme of the real suspend job is as follows.
-
- <orderedlist>
- <listitem><para>Retrieve the card and the chip data.</para></listitem>
- <listitem><para>Call <function>snd_power_change_state()</function> with
- <constant>SNDRV_CTL_POWER_D3hot</constant> to change the
- power status.</para></listitem>
- <listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem>
- <listitem><para>If AC97 codecs are used, call
- <function>snd_ac97_suspend()</function> for each codec.</para></listitem>
- <listitem><para>Save the register values if necessary.</para></listitem>
- <listitem><para>Stop the hardware if necessary.</para></listitem>
- <listitem><para>Disable the PCI device by calling
- <function>pci_disable_device()</function>. Then, call
- <function>pci_save_state()</function> at last.</para></listitem>
- </orderedlist>
- </para>
-
- <para>
- A typical code would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int mychip_suspend(struct pci_dev *pci, pm_message_t state)
- {
- /* (1) */
- struct snd_card *card = pci_get_drvdata(pci);
- struct mychip *chip = card->private_data;
- /* (2) */
- snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
- /* (3) */
- snd_pcm_suspend_all(chip->pcm);
- /* (4) */
- snd_ac97_suspend(chip->ac97);
- /* (5) */
- snd_mychip_save_registers(chip);
- /* (6) */
- snd_mychip_stop_hardware(chip);
- /* (7) */
- pci_disable_device(pci);
- pci_save_state(pci);
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The scheme of the real resume job is as follows.
-
- <orderedlist>
- <listitem><para>Retrieve the card and the chip data.</para></listitem>
- <listitem><para>Set up PCI. First, call <function>pci_restore_state()</function>.
- Then enable the pci device again by calling <function>pci_enable_device()</function>.
- Call <function>pci_set_master()</function> if necessary, too.</para></listitem>
- <listitem><para>Re-initialize the chip.</para></listitem>
- <listitem><para>Restore the saved registers if necessary.</para></listitem>
- <listitem><para>Resume the mixer, e.g. calling
- <function>snd_ac97_resume()</function>.</para></listitem>
- <listitem><para>Restart the hardware (if any).</para></listitem>
- <listitem><para>Call <function>snd_power_change_state()</function> with
- <constant>SNDRV_CTL_POWER_D0</constant> to notify the processes.</para></listitem>
- </orderedlist>
- </para>
-
- <para>
- A typical code would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int mychip_resume(struct pci_dev *pci)
- {
- /* (1) */
- struct snd_card *card = pci_get_drvdata(pci);
- struct mychip *chip = card->private_data;
- /* (2) */
- pci_restore_state(pci);
- pci_enable_device(pci);
- pci_set_master(pci);
- /* (3) */
- snd_mychip_reinit_chip(chip);
- /* (4) */
- snd_mychip_restore_registers(chip);
- /* (5) */
- snd_ac97_resume(chip->ac97);
- /* (6) */
- snd_mychip_restart_chip(chip);
- /* (7) */
- snd_power_change_state(card, SNDRV_CTL_POWER_D0);
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- As shown in the above, it's better to save registers after
- suspending the PCM operations via
- <function>snd_pcm_suspend_all()</function> or
- <function>snd_pcm_suspend()</function>. It means that the PCM
- streams are already stoppped when the register snapshot is
- taken. But, remember that you don't have to restart the PCM
- stream in the resume callback. It'll be restarted via
- trigger call with <constant>SNDRV_PCM_TRIGGER_RESUME</constant>
- when necessary.
- </para>
-
- <para>
- OK, we have all callbacks now. Let's set them up. In the
- initialization of the card, make sure that you can get the chip
- data from the card instance, typically via
- <structfield>private_data</structfield> field, in case you
- created the chip data individually.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int __devinit snd_mychip_probe(struct pci_dev *pci,
- const struct pci_device_id *pci_id)
- {
- ....
- struct snd_card *card;
- struct mychip *chip;
- int err;
- ....
- err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
- ....
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
- ....
- card->private_data = chip;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
-
- When you created the chip data with
- <function>snd_card_create()</function>, it's anyway accessible
- via <structfield>private_data</structfield> field.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int __devinit snd_mychip_probe(struct pci_dev *pci,
- const struct pci_device_id *pci_id)
- {
- ....
- struct snd_card *card;
- struct mychip *chip;
- int err;
- ....
- err = snd_card_create(index[dev], id[dev], THIS_MODULE,
- sizeof(struct mychip), &card);
- ....
- chip = card->private_data;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
-
- </para>
-
- <para>
- If you need a space to save the registers, allocate the
- buffer for it here, too, since it would be fatal
- if you cannot allocate a memory in the suspend phase.
- The allocated buffer should be released in the corresponding
- destructor.
- </para>
-
- <para>
- And next, set suspend/resume callbacks to the pci_driver.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct pci_driver driver = {
- .name = KBUILD_MODNAME,
- .id_table = snd_my_ids,
- .probe = snd_my_probe,
- .remove = __devexit_p(snd_my_remove),
- #ifdef CONFIG_PM
- .suspend = snd_my_suspend,
- .resume = snd_my_resume,
- #endif
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Module Parameters -->
-<!-- ****************************************************** -->
- <chapter id="module-parameters">
- <title>Module Parameters</title>
- <para>
- There are standard module options for ALSA. At least, each
- module should have the <parameter>index</parameter>,
- <parameter>id</parameter> and <parameter>enable</parameter>
- options.
- </para>
-
- <para>
- If the module supports multiple cards (usually up to
- 8 = <constant>SNDRV_CARDS</constant> cards), they should be
- arrays. The default initial values are defined already as
- constants for easier programming:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
- static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
- static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- If the module supports only a single card, they could be single
- variables, instead. <parameter>enable</parameter> option is not
- always necessary in this case, but it would be better to have a
- dummy option for compatibility.
- </para>
-
- <para>
- The module parameters must be declared with the standard
- <function>module_param()()</function>,
- <function>module_param_array()()</function> and
- <function>MODULE_PARM_DESC()</function> macros.
- </para>
-
- <para>
- The typical coding would be like below:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #define CARD_NAME "My Chip"
-
- module_param_array(index, int, NULL, 0444);
- MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard.");
- module_param_array(id, charp, NULL, 0444);
- MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard.");
- module_param_array(enable, bool, NULL, 0444);
- MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard.");
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Also, don't forget to define the module description, classes,
- license and devices. Especially, the recent modprobe requires to
- define the module license as GPL, etc., otherwise the system is
- shown as <quote>tainted</quote>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- MODULE_DESCRIPTION("My Chip");
- MODULE_LICENSE("GPL");
- MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}");
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- How To Put Your Driver -->
-<!-- ****************************************************** -->
- <chapter id="how-to-put-your-driver">
- <title>How To Put Your Driver Into ALSA Tree</title>
- <section>
- <title>General</title>
- <para>
- So far, you've learned how to write the driver codes.
- And you might have a question now: how to put my own
- driver into the ALSA driver tree?
- Here (finally :) the standard procedure is described briefly.
- </para>
-
- <para>
- Suppose that you create a new PCI driver for the card
- <quote>xyz</quote>. The card module name would be
- snd-xyz. The new driver is usually put into the alsa-driver
- tree, <filename>alsa-driver/pci</filename> directory in
- the case of PCI cards.
- Then the driver is evaluated, audited and tested
- by developers and users. After a certain time, the driver
- will go to the alsa-kernel tree (to the corresponding directory,
- such as <filename>alsa-kernel/pci</filename>) and eventually
- will be integrated into the Linux 2.6 tree (the directory would be
- <filename>linux/sound/pci</filename>).
- </para>
-
- <para>
- In the following sections, the driver code is supposed
- to be put into alsa-driver tree. The two cases are covered:
- a driver consisting of a single source file and one consisting
- of several source files.
- </para>
- </section>
-
- <section>
- <title>Driver with A Single Source File</title>
- <para>
- <orderedlist>
- <listitem>
- <para>
- Modify alsa-driver/pci/Makefile
- </para>
-
- <para>
- Suppose you have a file xyz.c. Add the following
- two lines
- <informalexample>
- <programlisting>
-<![CDATA[
- snd-xyz-objs := xyz.o
- obj-$(CONFIG_SND_XYZ) += snd-xyz.o
-]]>
- </programlisting>
- </informalexample>
- </para>
- </listitem>
-
- <listitem>
- <para>
- Create the Kconfig entry
- </para>
-
- <para>
- Add the new entry of Kconfig for your xyz driver.
- <informalexample>
- <programlisting>
-<![CDATA[
- config SND_XYZ
- tristate "Foobar XYZ"
- depends on SND
- select SND_PCM
- help
- Say Y here to include support for Foobar XYZ soundcard.
-
- To compile this driver as a module, choose M here: the module
- will be called snd-xyz.
-]]>
- </programlisting>
- </informalexample>
-
- the line, select SND_PCM, specifies that the driver xyz supports
- PCM. In addition to SND_PCM, the following components are
- supported for select command:
- SND_RAWMIDI, SND_TIMER, SND_HWDEP, SND_MPU401_UART,
- SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, SND_AC97_CODEC.
- Add the select command for each supported component.
- </para>
-
- <para>
- Note that some selections imply the lowlevel selections.
- For example, PCM includes TIMER, MPU401_UART includes RAWMIDI,
- AC97_CODEC includes PCM, and OPL3_LIB includes HWDEP.
- You don't need to give the lowlevel selections again.
- </para>
-
- <para>
- For the details of Kconfig script, refer to the kbuild
- documentation.
- </para>
-
- </listitem>
-
- <listitem>
- <para>
- Run cvscompile script to re-generate the configure script and
- build the whole stuff again.
- </para>
- </listitem>
- </orderedlist>
- </para>
- </section>
-
- <section>
- <title>Drivers with Several Source Files</title>
- <para>
- Suppose that the driver snd-xyz have several source files.
- They are located in the new subdirectory,
- pci/xyz.
-
- <orderedlist>
- <listitem>
- <para>
- Add a new directory (<filename>xyz</filename>) in
- <filename>alsa-driver/pci/Makefile</filename> as below
-
- <informalexample>
- <programlisting>
-<![CDATA[
- obj-$(CONFIG_SND) += xyz/
-]]>
- </programlisting>
- </informalexample>
- </para>
- </listitem>
-
- <listitem>
- <para>
- Under the directory <filename>xyz</filename>, create a Makefile
-
- <example>
- <title>Sample Makefile for a driver xyz</title>
- <programlisting>
-<![CDATA[
- ifndef SND_TOPDIR
- SND_TOPDIR=../..
- endif
-
- include $(SND_TOPDIR)/toplevel.config
- include $(SND_TOPDIR)/Makefile.conf
-
- snd-xyz-objs := xyz.o abc.o def.o
-
- obj-$(CONFIG_SND_XYZ) += snd-xyz.o
-
- include $(SND_TOPDIR)/Rules.make
-]]>
- </programlisting>
- </example>
- </para>
- </listitem>
-
- <listitem>
- <para>
- Create the Kconfig entry
- </para>
-
- <para>
- This procedure is as same as in the last section.
- </para>
- </listitem>
-
- <listitem>
- <para>
- Run cvscompile script to re-generate the configure script and
- build the whole stuff again.
- </para>
- </listitem>
- </orderedlist>
- </para>
- </section>
-
- </chapter>
-
-<!-- ****************************************************** -->
-<!-- Useful Functions -->
-<!-- ****************************************************** -->
- <chapter id="useful-functions">
- <title>Useful Functions</title>
-
- <section id="useful-functions-snd-printk">
- <title><function>snd_printk()</function> and friends</title>
- <para>
- ALSA provides a verbose version of the
- <function>printk()</function> function. If a kernel config
- <constant>CONFIG_SND_VERBOSE_PRINTK</constant> is set, this
- function prints the given message together with the file name
- and the line of the caller. The <constant>KERN_XXX</constant>
- prefix is processed as
- well as the original <function>printk()</function> does, so it's
- recommended to add this prefix, e.g.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\n");
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- There are also <function>printk()</function>'s for
- debugging. <function>snd_printd()</function> can be used for
- general debugging purposes. If
- <constant>CONFIG_SND_DEBUG</constant> is set, this function is
- compiled, and works just like
- <function>snd_printk()</function>. If the ALSA is compiled
- without the debugging flag, it's ignored.
- </para>
-
- <para>
- <function>snd_printdd()</function> is compiled in only when
- <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is set. Please note
- that <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is not set as default
- even if you configure the alsa-driver with
- <option>--with-debug=full</option> option. You need to give
- explicitly <option>--with-debug=detect</option> option instead.
- </para>
- </section>
-
- <section id="useful-functions-snd-bug">
- <title><function>snd_BUG()</function></title>
- <para>
- It shows the <computeroutput>BUG?</computeroutput> message and
- stack trace as well as <function>snd_BUG_ON</function> at the point.
- It's useful to show that a fatal error happens there.
- </para>
- <para>
- When no debug flag is set, this macro is ignored.
- </para>
- </section>
-
- <section id="useful-functions-snd-bug-on">
- <title><function>snd_BUG_ON()</function></title>
- <para>
- <function>snd_BUG_ON()</function> macro is similar with
- <function>WARN_ON()</function> macro. For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_BUG_ON(!pointer);
-]]>
- </programlisting>
- </informalexample>
-
- or it can be used as the condition,
- <informalexample>
- <programlisting>
-<![CDATA[
- if (snd_BUG_ON(non_zero_is_bug))
- return -EINVAL;
-]]>
- </programlisting>
- </informalexample>
-
- </para>
-
- <para>
- The macro takes an conditional expression to evaluate.
- When <constant>CONFIG_SND_DEBUG</constant>, is set, the
- expression is actually evaluated. If it's non-zero, it shows
- the warning message such as
- <computeroutput>BUG? (xxx)</computeroutput>
- normally followed by stack trace. It returns the evaluated
- value.
- When no <constant>CONFIG_SND_DEBUG</constant> is set, this
- macro always returns zero.
- </para>
-
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Acknowledgments -->
-<!-- ****************************************************** -->
- <chapter id="acknowledgments">
- <title>Acknowledgments</title>
- <para>
- I would like to thank Phil Kerr for his help for improvement and
- corrections of this document.
- </para>
- <para>
- Kevin Conder reformatted the original plain-text to the
- DocBook format.
- </para>
- <para>
- Giuliano Pochini corrected typos and contributed the example codes
- in the hardware constraints section.
- </para>
- </chapter>
-</book>