another round of questions regarding modem

DISCUSSION Richard Dawson 2 participants 2 messages Jun 8, 2003

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Richard Dawson

author

2003-06-08 21:44 UTC #0 lore raw

Distribution: Linux 9.1

System: ALR Optima Pentium MMX, 116 MHz. (Why bother? Hey, with free software this machine is worth something! Besides, I'm trying to learn here.)

Modem US Robotics V.everything internal , ISA board. (Yup, a vastly over-priced Cadillac. I bought it several years ago when I was experiencing slow connections hoping it would help. Seemed to help.) The modem is plug-and-play or can be configured for specific serial port/interrupt.

Mandrake 9.1/s installation and hardware configuration tools don't probe the ISA bus, so neither the sound board nor the modem were detected. After a lot of googling I found that I needed to use sndconfig to configure the ISA sound board. Successful! That leaves the modem.

Of course sndconfig didn't find the modem or help with its configuration. I'm a little slow, but it finally dawned on me that perhaps if I simply (1) configured the modem to a specific port and (2) told kppp that the device was at that port I would be done.

The modem can be configured for com1, com2, com3, or com 4 (ttyS0, ttyS1, ttyS2, ttyS3) with the customary interrupts (4,3,4,3). I disabled Com 2 in the system BIOS, configured the modem for com2 (ttS1) with interrupt 3. I then checked the serial port (ttyS1) with setserial and found that it was configured for interrupt 5! Strange. (Interestingly enough, this is the interrupt used by the sound board.) Using setserial, I forced the interrupt to be interrupt 3. Finally, using the madrake configuration tool, I told kppp to use /dev/ttyS1 as the device. With all this done, the configuration tool offers me an opprotunity to query the modem. After a long pause it indicates there is no response from the modem. (Before running setserial, with linux associating IRQ 5 with ttyS1, the response is "modem busy." Recall, IRQ 5 is used by the sound card.)

So there is, of course, another wrinkle to this. The modem manual's depiction of the jumpers for setting com ports and IRQs is not consisten with the board layout! The date on the manual is several years earlier than the date on the modem itself! For the outrageous price of the modem it should at least have an up-to-date manual, but of course it doesn't. The manual posted on US Robotics web site is even older, and for the external modem only! This reduces me to trying random combinations of jumpers to try and get a response.

Something that is complicated by the fact that I have to use setserial each time I boot in order to have Linux use the "standard" IRQ for ttyS1. (ttyS0 is associated with IRQ3 as one might expect).

So my questions:

(1)  Am I missing something?  Am I barking up entirely the wrong tree?
(2)  Where can I put a setserial command in order that Linux boots up with IRQ 4 associated with ttyS1?
(3)  Has anyone else experienced this confusion with the modem that I am using?  (I have submitted a rquest for ino to US Robotics)
(4)  Anything else relevant that might help.

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Ray Olszewski

2003-06-08 22:25 UTC #1 lore raw

OK. Your dissatisfactions with the quality of USR's documentation are not really a Linux problem. SO I'll limit myself to the part of your message that is.

Assuming you do manage to get your modem configured to look like it is on the right IRQ and IObase for the traditional COM2 ...I'm actually a bit surprised to see that Mandrake does something to fiddle with the conventional settings for /dev/ttyS1. But ...

Quoted 1 line · Richard Dawson

Something that is complicated by the fact that I have to use setserial each time I boot in order to have Linux use the "standard" IRQ for ttyS1. (ttyS0 is associated with IRQ3 as one might expect).

This "one" would expect no such thing. ttyS0 is supposed to be the Linux analog to COM1, which means it should have these settings:

        kuryakin:~# setserial /dev/ttyS0
        /dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4

Similarly, ttyS1 is the analog to COM2, with these default settings:

        kuryakin:~# setserial /dev/ttyS1
        /dev/ttyS1, UART: 16550A, Port: 0x02f8, IRQ: 3

(The UART entry is not part of the default; the presence of a UART entry normally means that the kernel has actually found a serial device at that IRQ/IObase location.)

Quoted 2 lines

So my questions:
(1) Am I missing something? Am I barking up entirely the wrong tree?

If you are fiddling blindly with jumpers, it is likely that you are changing the IObase assignments in unpredictable ways. Both IRQ -AND- IObase have to match what setserial expects to access a serial device.

Quoted 1 line

(2) Where can I put a setserial command in order that Linux boots up with IRQ 4 associated with ttyS1?

In an init script. On my Debian systems, I add this sort of local stuff to
/etc/init.d/rclocal

and make a symlink pointing to that from

        /etc/rc2.d/S99zlocal

Init-directory setups vary a bit by distro, so you will have to check for the exact locations Mandrake uses to correspond to these.

(BTW, I assume you meant IRQ 3, not "IRQ 4", in the question.)

Quoted 2 lines

(3) Has anyone else experienced this confusion with the modem that I am using? (I have submitted a rquest for ino to US Robotics)
(4) Anything else relevant that might help.

I don't know your mobo, but if it has pci slots as well as isa alots, you might check the BIOS to make sure that IRQ 3 is being made available to isa-slot devices. Just disabling the on-mobo COM2 (IRQ3) serial port might not be enough to accomplish this.