[sysconfig1] PCI modem setup

  • From: "Burt Philp" <bphilp@xxxxxxxxxxxxxx>
  • To: "Sysconfig1 list" <sysconfig1@xxxxxxxxxxxxx>
  • Date: Wed, 28 Feb 2001 14:52:08 -0500

A student approached me who was having a problem setting up a modem using 
Linux. I was talking to another student who had had a similar problem which he 
solved. I asked him to pass on the solution which you will see below. I have 
not tested it so I hope his instructions are precise.
----- Original Message ----- 
From: Rob Shepley
To: bphilp@xxxxxxxxxxxxxxxxx 
Sent: Tuesday, February 27, 2001 7:05 PM
Subject: hey

Hey .. sorry I took so long to write this message.  Anyway .. To configure a 
PCI hardware-based Plug N Play (Jumperless) Modem, try the following.

First in your CMOS you will have to set Plug And Play OS to FALSE.  Doing this  
will cause the BIOS to assign IRQs to your devices instead of relying on 
Windows to do so.  If you are using a PS2 mouse and have no external serial 
devices it would be wise to also disable both COM1 and COM2 in your CMOS to 
free up some IRQ's.

Next, log into Linux as root.  Issue the following command

lspci -v |more

I list of the PCI devices installed on your computer will be listed.  Look for 
your modem.  Then look at what address your modem is using.  (It should say 
something like Port: B800).. Also take note of what irq your modem is using (it 
will also be displayed)

now, you must re-assign /dev/ttyS0 to this new address and irq.  To do that 
issue the following command:

setserial /dev/ttyS0 port 0xB800 uart 16550 irq 10.

The 0x prefix before the address just means that the following number is a 
hexadecimal value.  If all went successfully, your modem should be responding, 
and be detected by all dialup applications on ttyS0  .. remember to replace 
0xB800 by whatever address your modem is using .. (0x0378 is the default for 
COM1 in DOS I beleive)

This re-assigning of ttyS0 only stays in effect until the next shutdown/reboot, 
so it would be wise to put the setserial command in one of your startup 
scripts.  I found inserting the line at the end of my /etc/rc.local file worked 

hope this helps ..

Rob (Charles)


Burt Philp
Computer Systems Dept.
St. Clair College
Email: bphilp@xxxxxxxxxxxxxx
Tel.: 519-972-2727 Ext. 4688

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