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From: stevel@eleazar.dartmouth.edu (Steve Ligett)
Newsgroups: comp.os.minix
Subject: Re: Minix for the PS/2
Message-ID: <12117@dartvax.Dartmouth.EDU>
Date: 7 Feb 89 15:09:47 GMT
References: <1054@uvm-gen.UUCP>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: stevel@eleazar.dartmouth.edu (Steve Ligett)
Organization: Dartmouth College, Hanover, NH
Lines: 36

Ok, there are two methods of handling PS/2 interrupts that I know work:

1.  Silence in
dividual devices,
2.  Mask interrupts in the 8259,

a third, sounds good, but I don't recall if anyone has it working:

3.  Delay sending EOIs till the interrupt is handled in the device task.

Some thoughts I've had.

#1 was the most obvious to me, and is easy for all devices that I know
about except the floppy disk.  IBM has added registers and bits to make
it easier than it was (in PCs) for some devices, but has done away with
the bit (in the DOR) that made it easy for floppies.  In general this
method means writing a bit to a register (perhaps reading the reg first
and or-ing in the bit).

#2 works, but seems like using a sledge hammer to me.

#3 sounds the best to me now, and I wish I'd thought of it.

For methods 2 and 3 to work well, I think we have to look at setting the
8259 into Special Mask Mode (SSM).  Normally, acknowledging an interrupt
or masking an interrupt means that all lower level interrupts are masked
as well.  In SSM, just the level being serviced or masked in inhibited;
lower level interrupts are allowed.  This would let serial interrupts be
recognized when clock, hard disk, or keyboard interrupts are still being
handled.

(I've just gotten minix 1.2 going on my PC, and am now ready to try to
help with 1.3, rather than just provide ideas based on reading
databooks.)

Steve Ligett       steve.ligett@dartmouth.edu or
(decvax harvard linus true)!dartvax!steve.ligett