Date: Sat, 12 Nov 1994 09:41:15 -0500 (CDT)
From: Aaron Ucko <UCKO AT VAX1 DOT ROCKHURST DOT EDU>
Subject: Re: A question about writing interrupt handler in gcc
To: heilig AT cs DOT und DOT nodak DOT edu
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu
Organization: Rockhurst College; Kansas City, MO

>ALAN L HIGHTOWER says:
>>      How else will I change the vector table?  Using irq7 and not 
>> chaining the previous handler locks the system up cold.
>
>I don't recall there being anything important off IRQ7, unless your
>sound card driver needs to be called for every interrupt.  Did you
LPT1 uses IRQ7; perhaps Alan wanted interrupt-driven printing so he could do
something else in the foreground.
>forget to tell the pic that you were done servicing the interrupt?
>all interrupts are blocked until you tell it that it's ok to service
>more.  In general, at the end of your handler, you must send a 0x20 to
>port 0x20 for any IRQ and a 0x20 to (I'm not sure where) for IRQs
>8-15.
port 0xA0

--- Aaron Ucko (ucko AT vax1 DOT rockhurst DOT edu; finger for PGP public key) -=- httyp!
-=*=-Just because you're paranoid doesn't mean they aren't out to get you.-=*=-
Geek code 2.1 [finger hayden AT vax1 DOT mankato DOT msus DOT edu for explanation]: 
 GCS/M/S d(-) H s g+ p? !au a-- w+ v+ C++(+++)>++++ U-(S+)>++++ P+ L>++ 3(-) 
 E-(----) !N>++ K- W(--) M-(--) V(--) po-(--) Y+(++) t(+) !5 j R G tv--(-) 
 b+++ !D(--) B--(---) e>++++(*) u++(@) h!() f(+) r-(--)>+++ n+(-) y?