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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)
+
+
+