Very Computer

by **Greg Hankin** » Tue, 04 Jul 1995 04:00:00

Archive-name: linux/howto/serial/part1
Last-modified: 2 Jul 95

-----BEGIN PGP SIGNED MESSAGE-----

*** The Linux Serial HOWTO is posted automatically by the Linux
*** HOWTO coordinator, Greg Hankins <gr...@sunsite.unc.edu>. Please
*** direct any comments or questions about this HOWTO to the author,
*** Greg Hankins <greg.hank...@cc.gatech.edu>.

- --- BEGIN Linux Serial HOWTO part 1/2 ---

The Linux Serial HOWTO
by Greg Hankins, greg.hank...@cc.gatech.edu
v1.8a, 5 June 1995

This document describes how to set up serial communications devices
on a Linux box.

1. Introduction

This is the Linux Serial HOWTO. All about how to set up modems and
terminals under Linux, some serial tips, and troubleshooting.

1.1. Copyright

The Linux Serial HOWTO is copyright (C) 1993 - 1995 by Greg Hankins.
Linux HOWTO documents may be reproduced and distributed in whole or in
part, in any medium physical or electronic, as long as this copyright
notice is retained on all copies. Commercial redistribution is allowed
and encouraged; however, the author would like to be notified of any
such distributions.

All translations, derivative works, or aggregate works incorporating
any Linux HOWTO documents must be covered under this copyright notice.
That is, you may not produce a derivative work from a HOWTO and impose
additional restrictions on its distribution. Exceptions to these rules
may be granted under certain conditions; please contact the Linux
HOWTO coordinator at the address given below.

In short, we wish to promote dissemination of this information through
as many channels as possible. However, we do wish to retain copyright
on the HOWTO documents, and would like to be notified of any plans to
redistribute the HOWTOs.

If you have questions, please contact Greg Hankins, the Linux HOWTO
coordinator, at
gr...@sunsite.unc.edu via email, or at +1 404 853 9989.

1.2. Other sources of information

o man pages for: agetty(8), getty(1m), gettydefs(5), init(1),
login(1), mgetty(8), setserial(8)

o Your modem manual

o UUCP HOWTO: for information on setting up UUCP

o Printing HOWTO: for setting up a serial printer

o NET-2 HOWTO: all about networking, including SLIP, CSLIP, PLIP and
PPP

o BUPS HOWTO: setting up UPS boxen connected to your serial port

o Term HOWTO: everything you wanted to know about the term program

o USENET newsgroups:

comp.os.linux.advocacy Benefits of Linux compared to other operating systems.
comp.os.linux.announce Announcements important to the Linux community.
comp.os.linux.answers FAQs, How-To's, READMEs, etc. about Linux.
comp.os.linux.development.apps Writing Linux applications, porting to Linux.
comp.os.linux.development.system Linux kernels, device drivers, modules.
comp.os.linux.hardware Hardware compatibility with the Linux operating system.
comp.os.linux.misc Linux-specific topics not covered by other groups.
comp.os.linux.networking Networking and communications under Linux.
comp.os.linux.setup Linux installation and system administration.
comp.os.linux.x Linux X Window System servers, clients, libs and fonts.

o the Linux serial mailing list. To join, send email to
majord...@vger.rutgers.edu, with

``subscribe linux-serial'' in the message body. If you send
``help'' in the message body, you get a help message.

1.3. New versions of this document

New versions of the Serial-HOWTO will be placed on

sunsite.unc.edu (ftp://sunsite.unc.edu:/pub/Linux/docs/HOWTO/Serial-
HOWTO) and mirror sites. There are other formats, such as a
PostScript and dvi version in the other-formats directory. The Serial
HOWTO (http://sunsite.unc.edu/mdw/HOWTO/Serial-HOWTO.html) is also
available for WWW clients such as mosaic. It will also be posted
regularly to comp.os.linux.answers.

If you don't have FTP access, you can get Linux help files via email.
Bill Riemers runs a mail handler on his account. Send mail to
b...@physics.purdue.edu with a subject of ``help'' for more infomation,
and to get an index file.

1.4. Feedback

Please send me any questions, comments, suggestions, or additional
material. I'm always eager to hear about what you think about the
HOWTO. I'm also always on the lookout for improvements! Tell me
exactly what you don't understand, or what could be clearer. You can
reach me at greg.hank...@cc.gatech.edu via email. I can also be
reached at:

Greg Hankins

College of Computing

801 Atlantic Drive

Atlanta, GA 30332-0280

via snail mail, and at my home page
(http://www.cc.gatech.edu/staff/h/Greg.Hankins/) via the WWW.

Please include the version number of the Serial HOWTO when writing,
this is version 1.8a.

1.5. Disclaimer

Your milage may vary. The answers given may not work for all systems
and all setup combinations.

2. Supported serial hardware

Linux is known to work with the following serial hardware.

o standard PC serial boards (COM1 - COM4), to which external serial
devices (modems, serial mice, etc...) can be connected

o standard PC internal modems (COM1 - COM4)

o Quickpath Systems Port-Folio 550e (allows IRQs of 3, 4, 5, 9, 10,
11, 12, and 15)

2.1. Multiport serial boards (with 16450/16550A UARTs)

o AST FourPort and clones (4 port)

o Accent Async-4 (4 port)

o Arnet Multiport-8 (8 port)

o Bell Technologies HUB6 (6 port)

o Boca BB-1004 (4 port), BB-1008 (8 port), BB-2016 (16 port)

o Boca IOAT66 (6 port)

o Boca 2by4 (4S/2P)

o Computone ValuePort V4-ISA (AST FourPort compatible)

o PC-COMM (4 port)

o STB-4COM (4 port)

o Twincom ACI/550

o Usenet Serial Board II (4 port)

In general, Linux will support any serial board which uses a 8250,
16450, 16550, 16550A (or compatible) UART, or an internal modem which
emulates one of the above UARTs.

Special note on the BB-1004 and BB-1008, they do not support DCD and
RI lines, and thus are not usable for dialin modems. They will work
fine for all other purposes.

2.2. Intelligent multiport serial boards

o Comtrol RocketPort (36Mhz ASIC - 4, 8, 16 or 32 port) (contact
i...@comtrol.com or Comtrol's Home Page (http://www.comtrol.com).
Driver location: tsx-11.mit.edu/pub/linux/packages/comtrol)
o Computone IntelliPort II (16Mhz 80186 - 4, 8, or 16 port) Computone
IntelliPort II EXpandable (20Mhz 80186 - modular 16 - 64 port)
(pre-ALPHA driver, contact Michael H. Warfield,
m...@wittsend.atl.ga.us)

o Cyclades Cyclom 8Y (8 port), and 16Y (16 port) (Cirrus Logic
CD-1400 RISC UARTs) (contact cycla...@netcom.com)

o DigiBoard PC/Xe (12.5MHz 80186 processor - 2, 4, 8, or 16 port),
and PC/Xi (12.5MHz 80186 processor - 8, or 16 port) (contact Troy
De Jongh, tr...@digibd.com. Driver location:
ftp.digibd.com:/digiline/drivers/linux)

o Digiboard COM/Xi (10MHz 80188 processor - 4 or 8 port)

(pre-ALPHA driver contact Simon Park, s...@wimpol.demon.co.uk)

o Hayes ESP8 (8 port)

(pre-ALPHA driver, contact Dennis Boylan, den...@lan.com)

o Omega COMM-8 (8 port)

(contact Vance Petree, vpet...@infi.net)

o Specialix SIO - (modular, 4 - 32 port)

(ALPHA driver, contact Simon Allen, simonal...@cix.compulink.co.uk)

o Stallion EasyIO-4 (4 port), EasyIO-8 (8 port), and Stallion
EasyConnection (modular, 8 - 32 port) (Cirrus Logic CD-1400 RISC
UARTs) (contact Greg Ungerer, g...@stallion.oz.au)

Drivers for the Cyclades, DigiBoard, Stallion and Specialix boards can
be

found on sunsite.unc.edu:/pub/Linux/kernel/patches/serial and mirror
sites.

3. What are the names of the serial ports?

There are the 4 serial devices corresponding to COM1 - COM4:

/dev/cua0, /dev/ttyS0 (COM1) address 0x3f8 IRQ 4
/dev/cua1, /dev/ttyS1 (COM2) address 0x2f8 IRQ 3
/dev/cua2, /dev/ttyS2 (COM3) address 0x3e8 IRQ 4
/dev/cua3, /dev/ttyS3 (COM4) address 0x2e8 IRQ 3

The /dev/ttySN devices are for incoming connections and /dev/cuaN
devices for outgoing connections. N is the serial port number. In
this document, I refer to COM1 as ttyS0, COM2 as ttyS1, COM3 as ttyS2,
and COM4 as ttyS3. If I am refering to a specific device in /dev, I
will always prepend /dev to avoid confusing you.

On some installations, two extra devices will be created, /dev/modem
for your modem and /dev/mouse for your mouse. Both of these are
symbolic links to the appropriate /dev/cuaN device which you specified
during the installation (unless you have a bus mouse, then /dev/mouse
will point to the bus mouse device).

There has been some discussion on the merits of /dev/mouse and
/dev/modem. I strongly discourage the use of these links. In
particular, if you are planning on using your modem for dialin you
will run into problems because the lock files will not work correctly
if you use /dev/modem. Use them if you like, but be sure they point to
the right device.

3.1. Major and minor device numbers of serial devices in /dev

/dev/ttyS0 major 4, minor 64 /dev/cua0 major 5, minor 64
/dev/ttyS1 major 4, minor 65 /dev/cua1 major 5, minor 65
/dev/ttyS2 major 4, minor 66 /dev/cua2 major 5, minor 66
/dev/ttyS3 major 4, minor 67 /dev/cua3 major 5, minor 67

Note that all distributions should come with these devices already
made correctly.

3.1.1. Creating devices in /dev

If you don't have a device, you will have to create it with the mknod
command.

Example, suppose you needed to create devices for ttyS0:

linux# mknod -m 666 /dev/cua0 c 5 64
linux# mknod -m 666 /dev/ttyS0 c 4 64

You can also get the MAKEDEV script, available on the usual FTP sites.
...

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by **Greg Hankin** » Tue, 04 Jul 1995 04:00:00

Archive-name: linux/howto/serial/part2
Last-modified: 2 Jul 95

-----BEGIN PGP SIGNED MESSAGE-----

*** The Linux Serial HOWTO is posted automatically by the Linux
*** HOWTO coordinator, Greg Hankins <gr...@sunsite.unc.edu>. Please
*** direct any comments or questions about this HOWTO to the author,
*** Greg Hankins <greg.hank...@cc.gatech.edu>.

- --- BEGIN Linux Serial HOWTO part 2/2 ---

The UART itself can't do anything with the data, it just sends and
receives it. The CPU gets an interrupt from the serial device every
time a byte has been sent or received. The CPU then moves the
received byte out of the UART's buffer and into memory somewhere, or
gives the UART another byte to send. The 8250 and 16450 UARTs only
have a 1 byte buffer. That means, that every time 1 byte is sent or
received, the CPU is interrupted. At low rates, this is OK. But, at
high transfer rates, the CPU gets so busy dealing with the UART, that
is doesn't have time to tend to other tasks. In some cases, the CPU
does not get around to servicing the interrupt in time, and the byte
is overwritten, because they are coming in so fast.

That's where the 16550A UARTs are useful. These chips come with 16
byte FIFOs. This means that it can receive or transmit up to 16 bytes
before it has to interrupt the CPU. Not only can it wait, but the CPU
then can transfer all 16 bytes at a time. Although the interrupt
threshold is seldom set at 16, this is still a significant advantage
over the other UARTs, which only have the 1 byte buffer. The CPU
receives less interrupts, and is free to do other things. Data is not
lost, and everyone is happy. (There is also a 16550 UART, but it is
treated as a 16450)

In general, the 8250 and 16450 UARTs should be fine for speeds up to
38400 bps. At speeds greater than 38400 bps, you might start seeing
data loss, and a reduction in interactive response time. Other PC
operating systems (definition used loosely here), like DOS aren't
multitasking, so they might be able to cope better with 8250 or
16450s. That's why some people don't see data loss, until they switch
to Linux.

Non-UART, and intelligent multiport boards use DSP chips to do
additional buffering and control, thus relieving the CPU even more.
For example, the Cyclades Cyclom, and Stallion EasyIO boards use a
Cirrus Logic CD-1400 RISC chip.

Keep in mind that these dumb UART types are not bad, they just aren't
good for high speeds. You should have no problem connecting a
terminal, or a mouse to these UARTs. But, for a high speed modem, the
16550A is definately a must.

You can buy serial cards with the 16550A UARTs for a little more
money, just ask your dealer what type of UART is on the card. Or if
you want to upgrade your existing card, you can simply purchase 16550A
chips and replace your existing 16450 UARTs. They are pin-to-pin
compatible. Some cards come with socketed UARTs for this purpose, if
not you can solder. Note, that you'll probably save yourself a lot of
trouble by just getting a new card, if you've got the money, they are
under US$ 50.

14.4. /dev/ttySN devices? What's the real difference between the
/dev/cuaN and

The only difference is the way that the devices are opened. The
dialin devices /dev/ttySN are opened in blocking mode, until CD is
asserted (ie someone connects). So, when someone wants to use a
/dev/cuaN device, there is no conflict with a program watching the
/dev/ttySN device.

The distinction is made to allow dialin and dialout use of the same
serial port.

15. Troubleshooting

15.1. I keep getting ``line NNN of inittab invalid''.

Make sure you are using the correct syntax for your version of init.
The different init's that are out there use different syntax in the
/etc/inittab file. Make sure you are using the correct syntax for
your version of getty.

15.2. When I try to dial out, it says ``/dev/cuaN: Device or resource
busy''.

This problem can arise when DCD or DTR are not set correctly. DCD
should only be set when there is an actual connection (ie someone is
dialed in), not when getty is watching the port. Check to make sure
that your modem is configured to only set DCD when there is a
connection. DTR should be set whenever something is using, or
watching the line, like getty, kermit, or some other comm program.

Another common cause of ``device busy'' errors, is that you set up
your serial port with an interrupt already taken by something else.
As each device initializes, it asks Linux for permission to use its
hardware interrupt. Linux keeps track of which interrupt is assigned
to whom, and if your interrupt is already taken, your device won't be
able to initialize properly. The device really doesn't have much of
any way to tell you that this happened, except that when you try to
use it, it will return a ``device-busy'' error. Check the interrupts
on all of your cards (serial, ethernet, SCSI, etc.). Look for IRQ
conflicts.

15.3. I keep getting ``Id SN respawning too fast: disabled for 5 min-
utes''.

Make sure your modem is configured correctly. Look at registers E and
Q. This can occur when your modem is chatting with getty.

Make sure you are calling getty correctly from your /etc/inittab.
Using the wrong syntax or device names will cause serious problems.

This can also happen when the uugetty initialization is failing. Go
to the ``getty or uugetty still doesn't work'' question.

15.4. Serial devices are slow or serial devices can only send in one
direction.

You probably have an IRQ conflict. Make sure there are no IRQs being
shared. Check all your cards (serial, ethernet, SCSI, etc...). Make
sure the jumper settings, and the setserial parameters are correct for
all your serial devices.

15.5. respawn. My modem is hosed after someone hangs up, or uugetty
doesn't

This can happen when your modem doesn't reset when DTR is dropped. I
saw my RD and SD LEDs go nuts when this happened to me. You need to
have your modem reset. Most Hayes compatible modems do this with &D3,
but on my USR Courier, I had to set &D2 and S13=1. Check your modem
manual.

15.6. it just locks up. I have my terminal connected to my PC, but
after I type in a login name,

You probably don't have CLOCAL in your /etc/gettydefs entry for the
terminal, and you're probably not using a full null modem cable. You
need CLOCAL, which tells Linux to ignore modem control signals. Here
is what it should look like:

# 38400 bps Dumb Terminal entry
DT38400# B38400 CS8 CLOCAL # B38400 SANE -ISTRIP CLOCAL #@S @L login: #DT38400
# 19200 bps Dumb Terminal entry
DT19200# B19200 CS8 CLOCAL # B19200 SANE -ISTRIP CLOCAL #@S @L login: #DT19200
# 9600 bps Dumb Terminal entry
DT9600# B9600 CS8 CLOCAL # B9600 SANE -ISTRIP CLOCAL #@S @L login: #DT9600

Next, kill the getty process so a new one will be spawned with the new
entry.

15.7. At high speeds, my modem loses data.

If you are trying to run your modem at > 19200 bps, and you don't have
16550A UARTs, you should upgrade them. See section ``What are
UARTs?'' about UARTs.

15.8. them configured. On startup, Linux doesn't report the serial
devices the way I have

This is true. Linux does not do any IRQ detection on startup, it only
does serial device detection. Thus, disregard what it says about the
IRQ, because it's just assuming the standard IRQs. This is done,
because IRQ detection is unreliable, and can be fooled.

So, even though I have my ttyS2 set at IRQ 5, I still see

Jan 23 22:25:28 misfits vmunix: tty02 at 0x03e8 (irq = 4) is a 16550A

You have to use setserial to tell Linux the IRQ you are using.

15.9. rz and/or sz don't work when I call my Linux box on my modem.

If Linux looks for /dev/modem when you try to transfer files, look at
/etc/profile, and /etc/csh.cshrc. There are a bunch of aliases
defined there on some distributions, most notably Slackware. These
aliases mess up the zmodem programs. Take them out, or correct them.

15.10. My screen is printing funny looking characters.

This happens on virtual consoles when you send binary data to your
screen, or sometimes on serial connections. The way to fix this is to
type echo ^v^[c. For the control-character-impaired, thats echo
<ctrl>v<esc>c.

15.11. getty or uugetty still doesn't work.

There is a DEBUG option that comes with getty_ps. Edit your config
file /etc/conf.{uu}getty.ttySN and add DEBUG=NNN. Where NNN is one of
the following combination of numbers according to what you are trying
to debug:

D_OPT 001 option settings
D_DEF 002 defaults file processing
D_UTMP 004 utmp/wtmp processing
D_INIT 010 line initialization (INIT)
D_GTAB 020 gettytab file processing
D_RUN 040 other runtime diagnostics
D_RB 100 ringback debugging
D_LOCK 200 uugetty lockfile processing
D_SCH 400 schedule processing
D_ALL 777 everything

Setting DEBUG=010 is a good place to start.

If you are running syslogd, debugging info will appear in your log
files. If you aren't running syslogd info will appear in
/tmp/getty:ttySN for debugging getty and /tmp/uugetty:ttySN for
uugetty, and in /var/adm/getty.log. Look at the debugging info and
see what is going on. Most likely, you will need to tune some of the
parameters in your config file, and reconfigure your modem.

You could also try mgetty. Some people have better luck with it.

16. Contributions

There was no possible way to write this HOWTO alone. Although a lot
of the HOWTO is my writing, I have rewritten many contributions to
...

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Very Computer

Linux Serial HOWTO (part 1/2)

Linux Serial HOWTO (part 1/2)

Linux Serial HOWTO (part 1/2)