Path: utzoo!attcan!uunet!munnari!otc!metro!ditsyda!evans
From: evans@ditsyda.oz (Bruce Evans)
Newsgroups: comp.os.minix
Subject: Re: Help! Minix 1.3 & PS/2 Model 80
Summary: EOI too early
Message-ID: <1259@ditsyda.oz>
Date: 18 Jan 89 21:32:07 GMT
References: <1023@uvm-gen.UUCP> <1906@ast.cs.vu.nl>
Organization: CSIRO DIT Sydney, Australia
Lines: 27

In article <1907@ast.cs.vu.nl> ast@cs.vu.nl (Andy Tanenbaum) writes:
>I suspect what they are trying to say is that if the EOI is issued when the
>level-triggered interrupt is still asserted, you get another interrupt.

That must be it! The EOI is issued in interrupt(), which is the *first*
stage of interrupt handling.

>[...] The floppy disk
>controller must be given some sort of command to tell it to negate the
>interrupt.  Furthermore, every other device (clock, hard disk, network, 
>etc) that can generate interrupts has the same problem.

The floppy task must not be getting a chance to do this, because the
processor is interrupted again as soon as it finishes the low-level
interrupt handling. This does not happen for edge-triggered interrupts
since the device interrupt request remains asserted.

So, the solution may be simply to remove all the EOI's in proc.c and put
them in floppy.c. Similarly for *wini.c. The other drivers are probably
OK. All except clock.c are low level and already do their own EOI's, and
I think the clock interrupt turns off automatically.

The EOI's never belonged in proc.c anyway, since they are machine-dependent
(pc, at, ps, ...) while the rest is not. I put them elsewhere ages ago,
centralized in save(). Even worse for level triggered interrupts :-{.
-- 
Bruce Evans		evans@ditsyda.oz.au
D