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From: johnl@ima.ima.isc.com (John R. Levine)
Newsgroups: comp.os.minix
Subject: Re: Query about level-triggered interrupts on the PS/2
Message-ID: <3187@ima.ima.isc.com>
Date: 17 Jan 89 23:12:03 GMT
References: <1910@ast.cs.vu.nl>
Reply-To: johnl@ima.UUCP (John R. Levine)
Organization: Segue Software, Inc.
Lines: 22

Looking at my copy of the PS/2 technical reference, I see that you need to
do a little more to dismiss an interrupt than previously.  In general:

	... tell the device to turn off the interrupt request
	JMP $+2	; delay
	... send EOI to the interrupt controller
	JMP $+2 ; delay some more
	STI	; turn interrupts back on
	IRET	; go back to where you were interrupted

This code is supposed to work on ATs as well.

In the particular case of the diskette controller, the manual says nothing
about how you trigger and reset interrupts, but I suspect that the interrupt
request goes away when you read all of the status bytes back from the
controller.  You may need the JMP $+2 between IN instructions when reading
back the status bytes.  Also, the high bit of the status byte at port
address 3F0 tells whether there's an interrupt pending.  Perhaps a few
experiments with "debug" would show how to make the interrupt request go away.-- 
John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 492 3869
{ bbn | spdcc | decvax | harvard | yale }!ima!johnl, Levine@YALE.something
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