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- Proc Files of ALSA Drivers
- ==========================
- Takashi Iwai <tiwai@suse.de>
-
-General
--------
-
-ALSA has its own proc tree, /proc/asound. Many useful information are
-found in this tree. When you encounter a problem and need debugging,
-check the files listed in the following sections.
-
-Each card has its subtree cardX, where X is from 0 to 7. The
-card-specific files are stored in the card* subdirectories.
-
-
-Global Information
-------------------
-
-cards
- Shows the list of currently configured ALSA drivers,
- index, the id string, short and long descriptions.
-
-version
- Shows the version string and compile date.
-
-modules
- Lists the module of each card
-
-devices
- Lists the ALSA native device mappings.
-
-meminfo
- Shows the status of allocated pages via ALSA drivers.
- Appears only when CONFIG_SND_DEBUG=y.
-
-hwdep
- Lists the currently available hwdep devices in format of
- <card>-<device>: <name>
-
-pcm
- Lists the currently available PCM devices in format of
- <card>-<device>: <id>: <name> : <sub-streams>
-
-timer
- Lists the currently available timer devices
-
-
-oss/devices
- Lists the OSS device mappings.
-
-oss/sndstat
- Provides the output compatible with /dev/sndstat.
- You can symlink this to /dev/sndstat.
-
-
-Card Specific Files
--------------------
-
-The card-specific files are found in /proc/asound/card* directories.
-Some drivers (e.g. cmipci) have their own proc entries for the
-register dump, etc (e.g. /proc/asound/card*/cmipci shows the register
-dump). These files would be really helpful for debugging.
-
-When PCM devices are available on this card, you can see directories
-like pcm0p or pcm1c. They hold the PCM information for each PCM
-stream. The number after 'pcm' is the PCM device number from 0, and
-the last 'p' or 'c' means playback or capture direction. The files in
-this subtree is described later.
-
-The status of MIDI I/O is found in midi* files. It shows the device
-name and the received/transmitted bytes through the MIDI device.
-
-When the card is equipped with AC97 codecs, there are codec97#*
-subdirectories (described later).
-
-When the OSS mixer emulation is enabled (and the module is loaded),
-oss_mixer file appears here, too. This shows the current mapping of
-OSS mixer elements to the ALSA control elements. You can change the
-mapping by writing to this device. Read OSS-Emulation.txt for
-details.
-
-
-PCM Proc Files
---------------
-
-card*/pcm*/info
- The general information of this PCM device: card #, device #,
- substreams, etc.
-
-card*/pcm*/xrun_debug
- This file appears when CONFIG_SND_DEBUG=y and
- CONFIG_PCM_XRUN_DEBUG=y.
- This shows the status of xrun (= buffer overrun/xrun) and
- invalid PCM position debug/check of ALSA PCM middle layer.
- It takes an integer value, can be changed by writing to this
- file, such as
-
- # echo 5 > /proc/asound/card0/pcm0p/xrun_debug
-
- The value consists of the following bit flags:
- bit 0 = Enable XRUN/jiffies debug messages
- bit 1 = Show stack trace at XRUN / jiffies check
- bit 2 = Enable additional jiffies check
- bit 3 = Log hwptr update at each period interrupt
- bit 4 = Log hwptr update at each snd_pcm_update_hw_ptr()
- bit 5 = Show last 10 positions on error
- bit 6 = Do above only once
-
- When the bit 0 is set, the driver will show the messages to
- kernel log when an xrun is detected. The debug message is
- shown also when the invalid H/W pointer is detected at the
- update of periods (usually called from the interrupt
- handler).
-
- When the bit 1 is set, the driver will show the stack trace
- additionally. This may help the debugging.
-
- Since 2.6.30, this option can enable the hwptr check using
- jiffies. This detects spontaneous invalid pointer callback
- values, but can be lead to too much corrections for a (mostly
- buggy) hardware that doesn't give smooth pointer updates.
- This feature is enabled via the bit 2.
-
- Bits 3 and 4 are for logging the hwptr records. Note that
- these will give flood of kernel messages.
-
- When bit 5 is set, the driver logs the last 10 xrun errors and
- the proc file shows each jiffies, position, period_size,
- buffer_size, old_hw_ptr, and hw_ptr_base values.
-
- When bit 6 is set, the full xrun log is shown only once.
-
-card*/pcm*/sub*/info
- The general information of this PCM sub-stream.
-
-card*/pcm*/sub*/status
- The current status of this PCM sub-stream, elapsed time,
- H/W position, etc.
-
-card*/pcm*/sub*/hw_params
- The hardware parameters set for this sub-stream.
-
-card*/pcm*/sub*/sw_params
- The soft parameters set for this sub-stream.
-
-card*/pcm*/sub*/prealloc
- The buffer pre-allocation information.
-
-
-AC97 Codec Information
-----------------------
-
-card*/codec97#*/ac97#?-?
- Shows the general information of this AC97 codec chip, such as
- name, capabilities, set up.
-
-card*/codec97#0/ac97#?-?+regs
- Shows the AC97 register dump. Useful for debugging.
-
- When CONFIG_SND_DEBUG is enabled, you can write to this file for
- changing an AC97 register directly. Pass two hex numbers.
- For example,
-
- # echo 02 9f1f > /proc/asound/card0/codec97#0/ac97#0-0+regs
-
-
-USB Audio Streams
------------------
-
-card*/stream*
- Shows the assignment and the current status of each audio stream
- of the given card. This information is very useful for debugging.
-
-
-HD-Audio Codecs
----------------
-
-card*/codec#*
- Shows the general codec information and the attribute of each
- widget node.
-
-card*/eld#*
- Available for HDMI or DisplayPort interfaces.
- Shows ELD(EDID Like Data) info retrieved from the attached HDMI sink,
- and describes its audio capabilities and configurations.
-
- Some ELD fields may be modified by doing `echo name hex_value > eld#*`.
- Only do this if you are sure the HDMI sink provided value is wrong.
- And if that makes your HDMI audio work, please report to us so that we
- can fix it in future kernel releases.
-
-
-Sequencer Information
----------------------
-
-seq/drivers
- Lists the currently available ALSA sequencer drivers.
-
-seq/clients
- Shows the list of currently available sequencer clients and
- ports. The connection status and the running status are shown
- in this file, too.
-
-seq/queues
- Lists the currently allocated/running sequencer queues.
-
-seq/timer
- Lists the currently allocated/running sequencer timers.
-
-seq/oss
- Lists the OSS-compatible sequencer stuffs.
-
-
-Help For Debugging?
--------------------
-
-When the problem is related with PCM, first try to turn on xrun_debug
-mode. This will give you the kernel messages when and where xrun
-happened.
-
-If it's really a bug, report it with the following information:
-
- - the name of the driver/card, show in /proc/asound/cards
- - the register dump, if available (e.g. card*/cmipci)
-
-when it's a PCM problem,
-
- - set-up of PCM, shown in hw_parms, sw_params, and status in the PCM
- sub-stream directory
-
-when it's a mixer problem,
-
- - AC97 proc files, codec97#*/* files
-
-for USB audio/midi,
-
- - output of lsusb -v
- - stream* files in card directory
-
-
-The ALSA bug-tracking system is found at:
-
- https://bugtrack.alsa-project.org/alsa-bug/