IRQ conflict on SCO Open Desktop

Uwe Doering gemini at geminix.mbx.sub.org
Mon May 28 21:04:32 AEST 1990


davidsen at sixhub.UUCP (Wm E. Davidsen Jr) writes:

>In article <6119 at scorn.sco.COM> wul at sco.com writes:

>| | Is IRQ2 usable with SCO Unix? 
>| 
>| Yes.  The standard configuration for network cards used internally
>| with TCP/IP (3c501s, 3c503s, WD8003s) is IRQ2.

>  Right on! This buys you one more interrupt than many of the other UNIX
>versions support.

386/ix works with IRQ2, too. The only difficulty may be that you have to
remember that on AT and 386 boards IQR2 on the bus side corresponds to
IRQ9 on the software side. Therefor if you want to use a device on IRQ2
you have to tell UNIX (during the device installation) that it is on
IRQ9. If the configuration program won't let you do this you can change
it by hand in the /etc/conf/sdevice.d directory.

I myself have a serial card on IRQ2 for several month now, without any
problems. As the interrupt management is device independent in the UNIX
kernel it doesn't matter what card you actually have on IRQ2.

There is one thing to consider, though. Most EGA and VGA cards use IRQ2
for their vertical retrace interrupt. This interrupt is absolutely
unnecessary under UNIX, and I don't know any DOS programs that need this
IRQ, either. It's there simply for compatibility reasons with the original
IBM EGA card. You have to disable this IRQ on these cards. Some have a
jumper for that purpose, but on most you have to cut the track that leads
to the B4 bus contact (it's the fourth contact on the solder side, counted
from the side where the monitor connector is). I have done this several
times and havn't had any problems from that.

     Uwe
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