Xref: news2.mv.net comp.os.msdos.djgpp:1618
From: Thomas Demmer <demmer AT LSTM DOT Ruhr-UNI-Bochum DOT De>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: interrupt levels vs interrupt to service
Date: Fri, 01 Mar 1996 16:07:40 +0100
Organization: Lehrstuhl fuer Stroemungsmechanik
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

James T. Sweeten Jr. wrote:
> 
>         What is the difference between an interrupt level and the
> interrupt number I use with my interrupt service routine.
> 

The PC interrupt controller (PIC) has several levels, that is an
interrupt with a higher priority  may disturb one with a lower priority. 
The priority is 0,1,9,a-f,3-7, with 0 the highest. IRQ 2 is used to fire
off the second PIC and cannot be used by devices. 
Each IRQ is wired to an Interrupt number, the one you may call with INT
xx. You get from IRQ to INT # by adding 8, if IRQ < 8, and adding 0x68,
if IRQ>=8.If I remember right, this might be changed, but that's not
recommended.


Ciao