Date: Mon, 10 Oct 1994 22:04:07 -0500 (CDT)
From: Aaron Ucko <UCKO AT VAX1 DOT ROCKHURST DOT EDU>
Subject: Re: Interrupt handling
To: dtauritz AT WI DOT LeidenUniv DOT NL
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu
Organization: Rockhurst College; Kansas City, MO

>I'm trying to write an interrupt handler in C like the example provided in
>  djgpp\samples\dpmi\timer.c
>In my program everything works when I select software interrupt 8 (timer
>interrupt) but not when I select software interrupt 72 (IRQ 10). While I
>really have hardcoded an interrupt generation via my soundcard which is
>installed for IRQ 10...
>In the file sb.c (djgpp/contrib/sblaster) both protected mode and real mode
>interrupt handlers are installed. Why is this? I thought DJGPP was a
>protected mode only package! Anyway, I wrote something similar to the real &

Yes, but suppose the interrupt is called when the computer is simulating a real
mode DOS/BIOS call.  We wouldn't want to cause a big pile-up, now would we? :-)

>protected mode combo used in sb.c, alas, without success, my interrupt
>handler installs without giving an error but the installed interrupt routine
>is never called...
>Any suggestions would be very much appreciated.

Well, the only difference I can think of is that with IRQs 8-15 you have to
reset both PIC2 and PIC1 (because of the IRQ2 cascade), but even so, you should
have been called at least once--or maybe you _were_ called once in the first
set of tests and nothing ever reset PIC2 (because no interrupts thru it could
be generated--kind of a vicious cycle).  Just my demi-nibble.  :-)

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