Running RHEL5.5 on a Dell R710 server. I installed a 2-port PCIe serial card, built the driver, and installed the kernel module. The ports show up in /etc/hwconf, lspci, kudzu, /proc/ioports, etc., and I now have two new device entries...

/dev/ttyE0
/dev/ttyE1

When I connect a null modem cable from port 0 of the card in the new computer to serial 0 of another computer, I can receive text from the other computer. When I do this...

# cat /dev/ttyE0 (on the new computer)
# echo hello > /dev/ttyS0 (on the other computer)

...then 'hello' shows up on the console of the new computer. However, when I reverse the process and do...

# cat /dev/ttyS0 (on the other computer)
# echo hello > /dev/ttyE0 (on the new computer)

...then nothing happens!

Any ideas would be appreciated.

I seem to recall reading that it is not advisable (system security issue) to have a port open for two-way communication. Therefore, the system is set up to use one port for outgoing only, and another for incoming only for a given device. That makes it easier to put limits on what comes in without affecting what goes out.

Since two device files were created, perhaps one is for outgoing and the other for incoming. Try sending on /dev/ttyE0 and receiving on /dev/ttyE1.

PS: I've googled but can't seem to find anything to substantiate my comments above.

Thanks for trying, but those are definitely not the issues. I have other servers that are working just fine, and even these servers work just fine if I use the built-in serial ports (/dev/ttyS0). The only problem is with the serial ports on the ad-in PCIe card.

Best,