Problem with IRQ2 and SCO Unix solved

[Anthony Shipman]

This is a reply to thank the people who helped and to report what I have
learned:

/--
| Is IRQ2 usable with SCO Unix? 
\--

 wul at sco.com (Wu Liu -- Member, Technical Staff The Santa Cruz Operation, Inc.)
replied:

> Yes.  The standard configuration for network cards used internally
> with TCP/IP (3c501s, 3c503s, WD8003s) is IRQ2.
> 
> I haven't tried setting a tape controller to use IRQ2; all of the tape
> drives I've configured have been set for IRQ5, or in one case, IRQ7.
> I'll have to give this a try sometime...

It turns out I had a hardware problem. The vital clue was:

> From: gemini at geminix.mbx.sub.org (Uwe Doering)
> 
> 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.
> 
> 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.
> 

Cutting the IRQ2 line (edge connector B4) solved the problem. Both the tape
controller and 3com ethernet board now work fine at IRQ2. I have settled on the
ethernet board at IRQ2=9 and the tape controller at IRQ5 to give the ethernet
board a higher priority. I don't know how important this is but it sounds good
(and it's the standard SCO configuration).


/-- 
| How can I use IRQ3 or IRQ4?
\--

Again a hardware problem. The motherboard still had the serial ports connected 
to IRQ3,4. I haven't tried it but I expect that all I had to do was disable the
serial ports in both software and hardware. 


-- 
Anthony Shipman                               ACSnet: als at bohra.cpg.oz.au
Computer Power Group
9th Flr, 616 St. Kilda Rd.,
St. Kilda, Melbourne, Australia
D