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-
- sx.txt -- specialix SX/SI multiport serial driver readme.
-
-
-
- Copyright (C) 1997 Roger Wolff (R.E.Wolff@BitWizard.nl)
-
- Specialix pays for the development and support of this driver.
- Please DO contact support@specialix.co.uk if you require
- support.
-
- This driver was developed in the BitWizard linux device
- driver service. If you require a linux device driver for your
- product, please contact devices@BitWizard.nl for a quote.
-
- (History)
- There used to be an SI driver by Simon Allan. This is a complete
- rewrite from scratch. Just a few lines-of-code have been snatched.
-
- (Sources)
- Specialix document number 6210028: SX Host Card and Download Code
- Software Functional Specification.
-
- (Copying)
- This program is free software; 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.
-
- This program is distributed in the hope that it will be
- useful, but WITHOUT ANY WARRANTY; without even the implied
- warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
- PURPOSE. See the GNU General Public License for more details.
-
- 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., 675 Mass Ave, Cambridge, MA 02139,
- USA.
-
- (Addendum)
- I'd appreciate it that if you have fixes, that you send them
- to me first.
-
-
-Introduction
-============
-
-This file contains some random information, that I like to have online
-instead of in a manual that can get lost. Ever misplace your Linux
-kernel sources? And the manual of one of the boards in your computer?
-
-
-Theory of operation
-===================
-
-An important thing to know is that the driver itself doesn't have the
-firmware for the card. This means that you need the separate package
-"sx_firmware". For now you can get the source at
-
- ftp://ftp.bitwizard.nl/specialix/sx_firmware_<version>.tgz
-
-The firmware load needs a "misc" device, so you'll need to enable the
-"Support for user misc device modules" in your kernel configuration.
-The misc device needs to be called "/dev/specialix_sxctl". It needs
-misc major 10, and minor number 167 (assigned by HPA). The section
-on creating device files below also creates this device.
-
-After loading the sx.o module into your kernel, the driver will report
-the number of cards detected, but because it doesn't have any
-firmware, it will not be able to determine the number of ports. Only
-when you then run "sx_firmware" will the firmware be downloaded and
-the rest of the driver initialized. At that time the sx_firmware
-program will report the number of ports installed.
-
-In contrast with many other multi port serial cards, some of the data
-structures are only allocated when the card knows the number of ports
-that are connected. This means we won't waste memory for 120 port
-descriptor structures when you only have 8 ports. If you experience
-problems due to this, please report them: I haven't seen any.
-
-
-Interrupts
-==========
-
-A multi port serial card, would generate a horrendous amount of
-interrupts if it would interrupt the CPU for every received
-character. Even more than 10 years ago, the trick not to use
-interrupts but to poll the serial cards was invented.
-
-The SX card allow us to do this two ways. First the card limits its
-own interrupt rate to a rate that won't overwhelm the CPU. Secondly,
-we could forget about the cards interrupt completely and use the
-internal timer for this purpose.
-
-Polling the card can take up to a few percent of your CPU. Using the
-interrupts would be better if you have most of the ports idle. Using
-timer-based polling is better if your card almost always has work to
-do. You save the separate interrupt in that case.
-
-In any case, it doesn't really matter all that much.
-
-The most common problem with interrupts is that for ISA cards in a PCI
-system the BIOS has to be told to configure that interrupt as "legacy
-ISA". Otherwise the card can pull on the interrupt line all it wants
-but the CPU won't see this.
-
-If you can't get the interrupt to work, remember that polling mode is
-more efficient (provided you actually use the card intensively).
-
-
-Allowed Configurations
-======================
-
-Some configurations are disallowed. Even though at a glance they might
-seem to work, they are known to lockup the bus between the host card
-and the device concentrators. You should respect the drivers decision
-not to support certain configurations. It's there for a reason.
-
-Warning: Seriously technical stuff ahead. Executive summary: Don't use
-SX cards except configured at a 64k boundary. Skip the next paragraph.
-
-The SX cards can theoretically be placed at a 32k boundary. So for
-instance you can put an SX card at 0xc8000-0xd7fff. This is not a
-"recommended configuration". ISA cards have to tell the bus controller
-how they like their timing. Due to timing issues they have to do this
-based on which 64k window the address falls into. This means that the
-32k window below and above the SX card have to use exactly the same
-timing as the SX card. That reportedly works for other SX cards. But
-you're still left with two useless 32k windows that should not be used
-by anybody else.
-
-
-Configuring the driver
-======================
-
-PCI cards are always detected. The driver auto-probes for ISA cards at
-some sensible addresses. Please report if the auto-probe causes trouble
-in your system, or when a card isn't detected.
-
-I'm afraid I haven't implemented "kernel command line parameters" yet.
-This means that if the default doesn't work for you, you shouldn't use
-the compiled-into-the-kernel version of the driver. Use a module
-instead. If you convince me that you need this, I'll make it for
-you. Deal?
-
-I'm afraid that the module parameters are a bit clumsy. If you have a
-better idea, please tell me.
-
-You can specify several parameters:
-
- sx_poll: number of jiffies between timer-based polls.
-
- Set this to "0" to disable timer based polls.
- Initialization of cards without a working interrupt
- will fail.
-
- Set this to "1" if you want a polling driver.
- (on Intel: 100 polls per second). If you don't use
- fast baud rates, you might consider a value like "5".
- (If you don't know how to do the math, use 1).
-
- sx_slowpoll: Number of jiffies between timer-based polls.
- Set this to "100" to poll once a second.
- This should get the card out of a stall if the driver
- ever misses an interrupt. I've never seen this happen,
- and if it does, that's a bug. Tell me.
-
- sx_maxints: Number of interrupts to request from the card.
- The card normally limits interrupts to about 100 per
- second to offload the host CPU. You can increase this
- number to reduce latency on the card a little.
- Note that if you give a very high number you can overload
- your CPU as well as the CPU on the host card. This setting
- is inaccurate and not recommended for SI cards (But it
- works).
-
- sx_irqmask: The mask of allowable IRQs to use. I suggest you set
- this to 0 (disable IRQs all together) and use polling if
- the assignment of IRQs becomes problematic. This is defined
- as the sum of (1 << irq) 's that you want to allow. So
- sx_irqmask of 8 (1 << 3) specifies that only irq 3 may
- be used by the SX driver. If you want to specify to the
- driver: "Either irq 11 or 12 is ok for you to use", then
- specify (1 << 11) | (1 << 12) = 0x1800 .
-
- sx_debug: You can enable different sorts of debug traces with this.
- At "-1" all debugging traces are active. You'll get several
- times more debugging output than you'll get characters
- transmitted.
-
-
-Baud rates
-==========
-
-Theoretically new SXDCs should be capable of more than 460k
-baud. However the line drivers usually give up before that. Also the
-CPU on the card may not be able to handle 8 channels going at full
-blast at that speed. Moreover, the buffers are not large enough to
-allow operation with 100 interrupts per second. You'll have to realize
-that the card has a 256 byte buffer, so you'll have to increase the
-number of interrupts per second if you have more than 256*100 bytes
-per second to transmit. If you do any performance testing in this
-area, I'd be glad to hear from you...
-
-(Psst Linux users..... I think the Linux driver is more efficient than
-the driver for other OSes. If you can and want to benchmark them
-against each other, be my guest, and report your findings...... :-)
-
-
-Ports and devices
-=================
-
-Port 0 is the top connector on the module closest to the host
-card. Oh, the ports on the SXDCs and TAs are labelled from 1 to 8
-instead of from 0 to 7, as they are numbered by linux. I'm stubborn in
-this: I know for sure that I wouldn't be able to calculate which port
-is which anymore if I would change that....
-
-
-Devices:
-
-You should make the device files as follows:
-
-#!/bin/sh
-# (I recommend that you cut-and-paste this into a file and run that)
-cd /dev
-t=0
-mknod specialix_sxctl c 10 167
-while [ $t -lt 64 ]
- do
- echo -n "$t "
- mknod ttyX$t c 32 $t
- mknod cux$t c 33 $t
- t=`expr $t + 1`
-done
-echo ""
-rm /etc/psdevtab
-ps > /dev/null
-
-
-This creates 64 devices. If you have more, increase the constant on
-the line with "while". The devices start at 0, as is customary on
-Linux. Specialix seems to like starting the numbering at 1.
-
-If your system doesn't come with these devices pre-installed, bug your
-linux-vendor about this. They should have these devices
-"pre-installed" before the new millennium. The "ps" stuff at the end
-is to "tell" ps that the new devices exist.
-
-Officially the maximum number of cards per computer is 4. This driver
-however supports as many cards in one machine as you want. You'll run
-out of interrupts after a few, but you can switch to polled operation
-then. At about 256 ports (More than 8 cards), we run out of minor
-device numbers. Sorry. I suggest you buy a second computer.... (Or
-switch to RIO).
-
-------------------------------------------------------------------------
-
-
- Fixed bugs and restrictions:
- - Hangup processing.
- -- Done.
-
- - the write path in generic_serial (lockup / oops).
- -- Done (Ugly: not the way I want it. Copied from serial.c).
-
- - write buffer isn't flushed at close.
- -- Done. I still seem to lose a few chars at close.
- Sorry. I think that this is a firmware issue. (-> Specialix)
-
- - drain hardware before changing termios
- - Change debug on the fly.
- - ISA free irq -1. (no firmware loaded).
- - adding c8000 as a probe address. Added warning.
- - Add a RAMtest for the RAM on the card.c
- - Crash when opening a port "way" of the number of allowed ports.
- (for example opening port 60 when there are only 24 ports attached)
- - Sometimes the use-count strays a bit. After a few hours of
- testing the use count is sometimes "3". If you are not like
- me and can remember what you did to get it that way, I'd
- appreciate an Email. Possibly fixed. Tell me if anyone still
- sees this.
- - TAs don't work right if you don't connect all the modem control
- signals. SXDCs do. T225 firmware problem -> Specialix.
- (Mostly fixed now, I think. Tell me if you encounter this!)
-
- Bugs & restrictions:
-
- - Arbitrary baud rates. Requires firmware update. (-> Specialix)
-
- - Low latency (mostly firmware, -> Specialix)
-
-
-