Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!zephyr!tektronix!tekcrl!tekgvs!keithe
From: keithe@tekgvs.LABS.TEK.COM (Keith Ericson)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Two Reply's: HW interrupts and COM port's
Message-ID: <5380@tekgvs.LABS.TEK.COM>
Date: 19 Jun 89 00:54:08 GMT
References: <2073@iesd.dk> <1506@cbnewsh.ATT.COM>
Reply-To: keithe@tekgvs.LABS.TEK.COM (Keith Ericson)
Distribution: na
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 27

In article <1506@cbnewsh.ATT.COM> rkl@cbnewsh.ATT.COM (kevin.laux) writes:
>
>On at AT
>class machine, you can't use IRQ 2, because that's used for the interrupt
                ^^^^^^^^^^^^^^^^^^^
>from the second PIC (Programmable Interrupt Controller), or, if you have
>and EGA/VGA card installed, the video card takes over IRQ 2 for itself (and
>then has to do the work of intercepting and passing on the interrupts from
>the second PIC).
>

Well, this comes as news to me - and to my AT...

I've got my WD8003 network card set up for IRQ2; and I've got a VGA diskplay
card.  It all works fine.

IRQ2 ends up as IRQ9 - take a look at diagrams for a PC bus and for an AT
bus and you'll see that IRQ2 on the PC bus has been replaced by IRQ9 on the
AT.  By the way - the same hardware configuration (network card jumpered for
IRQ2) works with DOS application (PC-NFS) configured for IRQ2 and for UNIX
(AT&T SysVR3.2), but UNIX refers to the interrupt as IRQ9.

kEITHe

PS - Actually, kevin's statement IS correct: "You can't use IRQ2" on an AT
     class machine because it doesn't really exist.  It's just that
     PC-oriented software still refers to it as IRQ2.