From: drew@caesar.cs.colorado.edu (Drew Eckhardt) Subject: Re: IBM PS/2 Model 70 Date: 13 Apr 1992 13:09:40 GMT
In article <VFq3iB4w164w@pdnfido.fidonet.org> erik@pdnfido.fidonet.org (erik vanriper) writes:
>Hello all!
>
> I have a "half a computer" at work that I have tried to boot up with
>Linux (0.95c) on a floppy, but to no avail. I get the initial "loading",
>get to the screen asking me what video mode I want, (does not matter what I
>enter at this point), and everything dies.
>
> If anyone has any suggestions, I would appreciate it.
>
As far as I can tell, the only differences between Microchannel and
ISA as far as systems software is concerned are the way interrupts are
handled, and IRQ lines assigned to serial ports.
ISA uses edge triggered interrupts, with IRQ lines tristated. This
is somewhat braindead, as multiple devices cannot share the same IRQ line.
If drivers are enabled on more than one, and one goes high, the other
remains low.... they short each other out.
MCA did interrupts right, and does level-active interrupts, with
IRQ lines open collector. Multiple devices can pull an IRQ low,
and IRQ lines can be shared.
Serial ports :
Everything after COM2: shares the same IRQ line, even or odd.
These changes should be quite trivial - you will need to change the
8259 PIC programming to be level triggered, rather than edge triggered.
If someone has a way to tell the difference between a MC PS/2 and an
ISA system, this could even be incorporated into the standard
release with only a few lines of code.