From: Guenter Resch (
Date: 11/06/03

  • Next message: Phil: "Re: 2nd USB printer fails"
    Date: 06 Nov 2003 09:21:30 GMT

    Hi everyone,

    I'm trying to set up a PCMCIA modem ("Mercury 56k Fax Modem Card", FCC
    ID 5HRTAI-31904-M5-E) to work on a Linux notebook with a customised
    kernel 2.4.21. In principle, the Modem does work as /dev/ttyS1, but
    it's extremely slow.auf einem System mit einem angepassten

    Based on what I read in the PCMCIA Howto, the problem is most likely an
    interrupt conflict:

    | If the modem seems to work only very, very slowly, this is an almost
    | certain indicator of an interrupt conflict.

    However, at the moment, the modem seems not to use and interrupt but is
    "working" in polled mode (IRQ 0):

            [root@eclipse pcmcia] setserial /dev/ttyS1
            /dev/ttyS1, UART: 16550A, Port: 0x02f8, IRQ: 0

    This is most likely the main reason of my problem. From the PCMCIA-Howto:

    | ... try using setserial to change the irq to 0, and see if the modem
    | works. This causes the serial driver to use a slower polled mode
    | instead of using interrupts.

    I think I should also mention the output of cardctl, where no IRQ is
    shown for the modem in socket 1:

            [root@eclipse pcmcia] cardctl config
            Socket 0:
             Vcc 3.3V Vpp1 3.3V Vpp2 3.3V
              interface type is "cardbus"
              irq 10 [exclusive] [level]
              function 0:
            Socket 1:
              Vcc 5.0V Vpp1 0.0V Vpp2 0.0V
              interface type is "memory and I/O"
              speaker output is enabled
              function 0:
              config base 0x0100
              option 0x61 status 0x08 ext 0x00
              io 0x02f8-0x02ff [8bit]

    So I have two questions:

    - How can I find a free IRQ? Is this just by looking for missing entries
      in /proc/interrupts? What irritated me a bit was that /dev/ttyS0 is on
      IRQ 4 (setserial) but not shown upon cat /proc/interrupts.

    - On a RedHat system, how do I assign the free IRQ I found to the modem
      correctly? Trying to change SERIAL_OPTS in /etc/pcmcia/serial.opts was
      not very successful (I could get the modem to use anIRQ but it did not
      work anymore).

    Thanks in advance,


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