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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 email@example.com if you require
+ 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.
+ 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.
+ Specialix document number 6210028: SX Host Card and Download Code
+ Software Functional Specification.
+ 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,
+ I'd appreciate it that if you have fixes, that you send them
+ to me first.
+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
+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.
+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).
+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
+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
+ 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
+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....
+You should make the device files as follows:
+# (I recommend that you cut-and-paste this into a file and run that)
+mknod specialix_sxctl c 10 167
+while [ $t -lt 64 ]
+ echo -n "$t "
+ mknod ttyX$t c 32 $t
+ mknod cux$t c 33 $t
+ t=`expr $t + 1`
+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)