linux/Documentation/serial/sx.txt
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   2      sx.txt  -- specialix SX/SI multiport serial driver readme.
   3
   4
   5
   6      Copyright (C) 1997  Roger Wolff (R.E.Wolff@BitWizard.nl)
   7
   8      Specialix pays for the development and support of this driver.
   9      Please DO contact support@specialix.co.uk if you require
  10      support.
  11
  12      This driver was developed in the BitWizard linux device
  13      driver service. If you require a linux device driver for your
  14      product, please contact devices@BitWizard.nl for a quote.
  15
  16      (History)
  17      There used to be an SI driver by Simon Allan. This is a complete 
  18      rewrite  from scratch. Just a few lines-of-code have been snatched.
  19
  20      (Sources)
  21      Specialix document number 6210028: SX Host Card and Download Code
  22      Software Functional Specification.
  23
  24      (Copying)
  25      This program is free software; you can redistribute it and/or
  26      modify it under the terms of the GNU General Public License as
  27      published by the Free Software Foundation; either version 2 of
  28      the License, or (at your option) any later version.
  29
  30      This program is distributed in the hope that it will be
  31      useful, but WITHOUT ANY WARRANTY; without even the implied
  32      warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
  33      PURPOSE.  See the GNU General Public License for more details.
  34
  35      You should have received a copy of the GNU General Public
  36      License along with this program; if not, write to the Free
  37      Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139,
  38      USA.
  39      
  40      (Addendum)
  41      I'd appreciate it that if you have fixes, that you send them
  42      to me first. 
  43
  44
  45Introduction
  46============
  47
  48This file contains some random information, that I like to have online
  49instead of in a manual that can get lost. Ever misplace your Linux
  50kernel sources?  And the manual of one of the boards in your computer?
  51
  52
  53Theory of operation
  54===================
  55
  56An important thing to know is that the driver itself doesn't have the
  57firmware for the card. This means that you need the separate package
  58"sx_firmware". For now you can get the source at
  59
  60        ftp://ftp.bitwizard.nl/specialix/sx_firmware_<version>.tgz
  61
  62The firmware load needs a "misc" device, so you'll need to enable the
  63"Support for user misc device modules" in your kernel configuration.
  64The misc device needs to be called "/dev/specialix_sxctl". It needs
  65misc major 10, and minor number 167 (assigned by HPA). The section
  66on creating device files below also creates this device. 
  67
  68After loading the sx.o module into your kernel, the driver will report
  69the number of cards detected, but because it doesn't have any
  70firmware, it will not be able to determine the number of ports. Only
  71when you then run "sx_firmware" will the firmware be downloaded and
  72the rest of the driver initialized. At that time the sx_firmware
  73program will report the number of ports installed.
  74
  75In contrast with many other multi port serial cards, some of the data
  76structures are only allocated when the card knows the number of ports
  77that are connected. This means we won't waste memory for 120 port
  78descriptor structures when you only have 8 ports. If you experience
  79problems due to this, please report them: I haven't seen any.
  80
  81
  82Interrupts
  83==========
  84
  85A multi port serial card, would generate a horrendous amount of
  86interrupts if it would interrupt the CPU for every received
  87character. Even more than 10 years ago, the trick not to use
  88interrupts but to poll the serial cards was invented.
  89
  90The SX card allow us to do this two ways. First the card limits its
  91own interrupt rate to a rate that won't overwhelm the CPU. Secondly,
  92we could forget about the cards interrupt completely and use the
  93internal timer for this purpose.
  94
  95Polling the card can take up to a few percent of your CPU. Using the
  96interrupts would be better if you have most of the ports idle. Using
  97timer-based polling is better if your card almost always has work to
  98do. You save the separate interrupt in that case.
  99
 100In any case, it doesn't really matter all that much. 
 101
 102The most common problem with interrupts is that for ISA cards in a PCI
 103system the BIOS has to be told to configure that interrupt as "legacy
 104ISA". Otherwise the card can pull on the interrupt line all it wants
 105but the CPU won't see this.
 106
 107If you can't get the interrupt to work, remember that polling mode is
 108more efficient (provided you actually use the card intensively).
 109
 110
 111Allowed Configurations
 112======================
 113
 114Some configurations are disallowed. Even though at a glance they might
 115seem to work, they are known to lockup the bus between the host card
 116and the device concentrators. You should respect the drivers decision
 117not to support certain configurations. It's there for a reason.
 118
 119Warning: Seriously technical stuff ahead. Executive summary: Don't use
 120SX cards except configured at a 64k boundary. Skip the next paragraph.
 121
 122The SX cards can theoretically be placed at a 32k boundary. So for
 123instance you can put an SX card at 0xc8000-0xd7fff. This is not a
 124"recommended configuration". ISA cards have to tell the bus controller
 125how they like their timing. Due to timing issues they have to do this
 126based on which 64k window the address falls into. This means that the
 12732k window below and above the SX card have to use exactly the same
 128timing as the SX card. That reportedly works for other SX cards. But
 129you're still left with two useless 32k windows that should not be used
 130by anybody else.
 131
 132
 133Configuring the driver
 134======================
 135
 136PCI cards are always detected. The driver auto-probes for ISA cards at
 137some sensible addresses. Please report if the auto-probe causes trouble
 138in your system, or when a card isn't detected.
 139
 140I'm afraid I haven't implemented "kernel command line parameters" yet.
 141This means that if the default doesn't work for you, you shouldn't use
 142the compiled-into-the-kernel version of the driver. Use a module
 143instead.  If you convince me that you need this, I'll make it for
 144you. Deal?
 145
 146I'm afraid that the module parameters are a bit clumsy. If you have a
 147better idea, please tell me.
 148
 149You can specify several parameters:
 150
 151        sx_poll: number of jiffies between timer-based polls.
 152
 153                Set this to "0" to disable timer based polls. 
 154                Initialization of cards without a working interrupt
 155                will fail.
 156
 157                Set this to "1" if you want a polling driver. 
 158                (on Intel: 100 polls per second). If you don't use
 159                fast baud rates, you might consider a value like "5". 
 160                (If you don't know how to do the math, use 1).
 161
 162        sx_slowpoll: Number of jiffies between timer-based polls. 
 163                Set this to "100" to poll once a second. 
 164                This should get the card out of a stall if the driver
 165                ever misses an interrupt. I've never seen this happen,
 166                and if it does, that's a bug. Tell me. 
 167
 168        sx_maxints: Number of interrupts to request from the card. 
 169                The card normally limits interrupts to about 100 per
 170                second to offload the host CPU. You can increase this
 171                number to reduce latency on the card a little.
 172                Note that if you give a very high number you can overload
 173                your CPU as well as the CPU on the host card. This setting 
 174                is inaccurate and not recommended for SI cards (But it 
 175                works). 
 176
 177        sx_irqmask: The mask of allowable IRQs to use. I suggest you set 
 178                this to 0 (disable IRQs all together) and use polling if 
 179                the assignment of IRQs becomes problematic. This is defined
 180                as the sum of (1 << irq) 's that you want to allow. So 
 181                sx_irqmask of 8 (1 << 3) specifies that only irq 3 may
 182                be used by the SX driver. If you want to specify to the 
 183                driver: "Either irq 11 or 12 is ok for you to use", then
 184                specify (1 << 11) | (1 << 12) = 0x1800 . 
 185
 186        sx_debug: You can enable different sorts of debug traces with this. 
 187                At "-1" all debugging traces are active. You'll get several
 188                times more debugging output than you'll get characters 
 189                transmitted. 
 190
 191
 192Baud rates
 193==========
 194
 195Theoretically new SXDCs should be capable of more than 460k
 196baud. However the line drivers usually give up before that.  Also the
 197CPU on the card may not be able to handle 8 channels going at full
 198blast at that speed. Moreover, the buffers are not large enough to
 199allow operation with 100 interrupts per second. You'll have to realize
 200that the card has a 256 byte buffer, so you'll have to increase the
 201number of interrupts per second if you have more than 256*100 bytes
 202per second to transmit.  If you do any performance testing in this
 203area, I'd be glad to hear from you...
 204
 205(Psst Linux users..... I think the Linux driver is more efficient than
 206the driver for other OSes. If you can and want to benchmark them
 207against each other, be my guest, and report your findings...... :-)
 208
 209
 210Ports and devices
 211=================
 212
 213Port 0 is the top connector on the module closest to the host
 214card. Oh, the ports on the SXDCs and TAs are labelled from 1 to 8
 215instead of from 0 to 7, as they are numbered by linux. I'm stubborn in
 216this: I know for sure that I wouldn't be able to calculate which port
 217is which anymore if I would change that....
 218
 219
 220Devices:
 221
 222You should make the device files as follows:
 223
 224#!/bin/sh
 225# (I recommend that you cut-and-paste this into a file and run that)
 226cd /dev
 227t=0
 228mknod specialix_sxctl c 10 167
 229while [ $t -lt 64 ]
 230  do 
 231  echo -n "$t "
 232  mknod ttyX$t c 32 $t
 233  mknod cux$t  c 33 $t
 234  t=`expr $t + 1`
 235done
 236echo ""
 237rm /etc/psdevtab
 238ps > /dev/null
 239
 240
 241This creates 64 devices. If you have more, increase the constant on
 242the line with "while". The devices start at 0, as is customary on
 243Linux. Specialix seems to like starting the numbering at 1. 
 244
 245If your system doesn't come with these devices pre-installed, bug your
 246linux-vendor about this. They should have these devices
 247"pre-installed" before the new millennium. The "ps" stuff at the end
 248is to "tell" ps that the new devices exist.
 249
 250Officially the maximum number of cards per computer is 4. This driver
 251however supports as many cards in one machine as you want. You'll run
 252out of interrupts after a few, but you can switch to polled operation
 253then. At about 256 ports (More than 8 cards), we run out of minor
 254device numbers. Sorry. I suggest you buy a second computer.... (Or
 255switch to RIO).
 256
 257------------------------------------------------------------------------
 258
 259
 260  Fixed bugs and restrictions:
 261        - Hangup processing.  
 262          -- Done.
 263
 264        - the write path in generic_serial (lockup / oops). 
 265          -- Done (Ugly: not the way I want it. Copied from serial.c).
 266
 267        - write buffer isn't flushed at close.
 268          -- Done. I still seem to lose a few chars at close. 
 269             Sorry. I think that this is a firmware issue. (-> Specialix)
 270
 271        - drain hardware before  changing termios
 272        - Change debug on the fly. 
 273        - ISA free irq -1. (no firmware loaded).
 274        - adding c8000 as a probe address. Added warning. 
 275        - Add a RAMtest for the RAM on the card.c
 276        - Crash when opening a port "way" of the number of allowed ports. 
 277          (for example opening port 60 when there are only 24 ports attached)
 278        - Sometimes the use-count strays a bit. After a few hours of
 279          testing the use count is sometimes "3". If you are not like
 280          me and can remember what you did to get it that way, I'd
 281          appreciate an Email. Possibly fixed. Tell me if anyone still
 282          sees this.
 283        - TAs don't work right if you don't connect all the modem control
 284          signals. SXDCs do. T225 firmware problem -> Specialix. 
 285          (Mostly fixed now, I think. Tell me if you encounter this!)
 286
 287  Bugs & restrictions:
 288
 289        - Arbitrary baud rates. Requires firmware update. (-> Specialix)
 290
 291        - Low latency (mostly firmware, -> Specialix)
 292
 293
 294
 295
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