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diff --git a/Documentation/serial/sx.txt b/Documentation/serial/sx.txt new file mode 100644 index 0000000..cb4efa0 --- /dev/null +++ b/Documentation/serial/sx.txt @@ -0,0 +1,294 @@ + + 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) + + + |