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Date: Fri, 20 Jun 2008 22:03:21 -0600 (MDT)
From: Nikolaus Vonessen <nikolaus@souza-vonessen.org>
To: Linmodems <discuss@linmodems.org>
Subject: PC Card Modem: resolved interrupt conflict and modem initialization
 problem
Message-ID: <alpine.DEB.1.00.0806202200450.7077@nv-ubuntu>
User-Agent: Alpine 1.00 (DEB 882 2007-12-20)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII

I managed to make my Zoom V.92 PC Card modem (Model 3075, the one with
an "L" in the serial number) work on my laptop under Ubuntu 8.04, and
thought I should report the solution since I had earlier asked the
list for advice.

There had actually been two problems:

        (1) an irq conflict, and

        (2) a modem initialization problem (caused, of all things, by
            the modem command ATZ used by wvdial).

Here are the details.


(1) My modem, /dev/ttyS0, uses irq 3 (as I discovered with setserial),
     but often either did not react at all, or very slowly.  The
     symptoms perfectly fit the description in Section 12.5 of the
     "Linux Serial HOWTO" ("Extremely Slow: Text appears on the screen
     slowly after long delays").  Setting the modem's irq to 0 with
     "sudo setserial /dev/ttyS0 irq 0" resolved this.  According to the
     Linux Serial HOWTO, this proved that there was indeed an irq
     conflict; it was stated there as well, however, that using irq 0
     is not a good idea.

     When I changed the irq of my modem (somewhat at random), the
     interrupt problem did not go away.

     To find the other device using irq 3 as well, I looked in the
     kernel log.  Found many entries (probably one per boot) of the
     form:

     "nsc_ircc_pnp_probe() : From PnP, found firbase 0x2F8 ; irq 3 ; dma 3"

     This seemed to indicate that nsc_ircc was the culprit also using
     irq 3.

     Googling, I found that nsc_ircc is an "irda module", where irda
     uses the infrared port.  So that's what I had to disable.  (I did
     not mind, since I am not using the infrared port.)  I had to make
     sure the kernel does not load the module irda.  By chance this was
     the example at

              http://wiki.debian.org/udev

     Following this example, I figured out with lsmod that irda uses
     (only) the module nsc_ircc.  So I created in the directory
     "/etc/modprobe.d" two one-line files

          1) "irda", with content "blacklist irda"

          2) "nsc_ircc", with content "blacklist nsc_ircc"

     Rebooted.  Now the kernel log did not mention irq 3 at all, and
     lsmod did not show either irda or nsc_ircc.  And from now on, the
     modem always reacted very fast.

(2) I had, however, still the following problem: Using "sudo wvdial",
     I could now successfully connect to my internet service provider.
     But whenever wvdial sent my username in response to the login
     prompt, the modem only transmitted some of the letters
     ("ooeeoer.Net" instead of "souzavonessen@Copper.Net").  I
     eventually discovered that this is caused by the ATZ command
     inserted in /etc/wvdial.conf by wvdialconf.  In /etc/wvdial.conf,
     I commented out all initialization commands.  Starting minicom
     once and then exiting resets the modem to usable defaults.
     Afterwords, "sudo wvdial" manages to establish working internet
     connections.  If for some reason the command ATZ is sent to the
     modem (I did this when testing), starting and exiting minicom
     resets the modem again.

My pc card modem is now working fine.

Many thanks to all of you who make linmodems.org and all its services
work!
Webmaster: Russell Nelson
Last modified: Wed Jul 30 11:02:43 EDT 2003