Printable Version of Topic

Click here to view this topic in its original format

Linuxhelp _ Hardware Support _ Serial ports not working under Linux

Posted by: DaveOz Sep 18 2011, 10:47 AM

Seems like a linux kernel or driver issue. We have a industrial type motherboard with 4 serial ports that will not work when running arch linux; and this problem has us stumped. The ports work with windows embedded, so we know the hardware is good. The super IO chip on the MB is old enough that drivers should not be a problem. And the flow control pins work (indicate the correct voltage) when set manually through a comms tool (coolterm). However we cannot get the ports to communicate with known good serial devices (that work with other computers and with the same MB running windows embedded). Also worth noting is the same harddrive with this linux OS can be booted on a different industrial board and those serial ports work fine. Also this problem occurs under both Arch Linux and Ubuntu.
The kernel is updated and auto compiled following update. setserial returns expected IRQ and address settings for the ports (matching up with bios settings), and running setserial with autoconfigure returns the same settings.
Only odd thing noticed is that dmesg shows two different IRQs for ttyS0 in two different lines, but the other ports do not shows up this way. All ports indicate connected when tested with coolterm, but again no data is ever transmitted or received successfully!!
Any ideas on the cause of this problem, or suggestions on how to better test are appreciated!!

Posted by: michaelk Sep 19 2011, 07:04 AM

Post the output of the command lspci
Did you swap drive to the same make/model of hardware?

I'm a bit confused. Can you communicate successfully to other serial devices with coolterm?

Posted by: DaveOz Sep 20 2011, 09:13 PM

Turns out all that was needed was to add pnpacpi=off to the kernel command line in /boot/grub/menu.lst. this turns off pnp management of the serial ports, which was disabling IRQ sharing that turns out to be required for the Super IO chip providing those ports.

Posted by: satsuke1 Nov 5 2011, 06:14 AM



Powered by Invision Power Board (
© Invision Power Services (