Home / server / Questions / 607482
Accepted
fadedbee
Asked: 2014-06-25 02:14:00 +0800 CST

Two port PCI serial card. One port can only set baud rate once

  • 772

I have a new PCI serial card, being used on a Ubuntu 14.04 box.

It's serial ports show up as /dev/ttyS4 and /dev/ttyS5.

$ dmesg | grep ttyS
[    0.732690] 00:03: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
[    0.733604] 0000:06:04.0: ttyS4 at I/O 0xd010 (irq = 16, base_baud = 115200) is a XScale
[    0.733700] 0000:06:04.0: ttyS5 at I/O 0xd000 (irq = 16, base_baud = 115200) is a XScale
$

I can set the baud rate of ttyS4 once after a reboot...

$ sudo /bin/stty -F /dev/ttyS4 115200
$

A second attempt yields an error...

$ sudo /bin/stty -F /dev/ttyS4 115200
/bin/stty: /dev/ttyS4: Input/output error
$

ttyS5 works fine...

$ sudo /bin/stty -F /dev/ttyS5 115200
$

and a second time...

$ sudo /bin/stty -F /dev/ttyS5 115200
$
linux

1 Answers

  1. Best Answer

    The problem was that the card was doing some sort of auto-baud detection on ttyS4 (which had a cable plugged in), but not on ttyS5 (which didn't).

    I've thrown the card away and am using a USB adapter now.

    • 1