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From: phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: sharing hardware interrupts
Message-ID: <1991May29.014824.16278@ux1.cso.uiuc.edu>
Date: 29 May 91 01:48:24 GMT
Organization: University of Illinois at Urbana
Lines: 23

I have read that two devices cannot share and concurrent use the same
interrupt (IRQ).  I'd like to know if this is really so true and if it
is more a case of just dumb software (which abounds in this world).

Suppose you have two or more different serial ports in a PC.  Surely
there is a register somewhere on there that indicates its status as to
whether or not it has changed state, or has a state that needs to be
dealt with.  When any one of the serial ports causes an interrupt (for
the sake of discussion let's say it is #4 and nothing else uses #4)
the software driver will get into control, scan all the known serial
port addresses for states to deal with, and performs the appropriate
action for all of them that need it.

Given the above software, why could it not be possible to have two or
more devices share the same interrupt.

I plan to write my own terminal program soon, and I want to make sure
that it is going to be able to handle all reasonable and useful cases.
-- 
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/ Phil Howard -- KA9WGN -- phil@ux1.cso.uiuc.edu   |  Guns don't aim guns at  \
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