On Tue, 19 Feb 2002, Joseph Sarkes wrote:

> > 
> > On Tue, Feb 19, 2002 at 07:28:39PM -0500, Joseph Sarkes wrote:
> > > trap type 200 at 30fc10
> > 
> > Ouch.  That's a "machine check" trap and might happen for one of a
> > couple of different reasons.
> 
> Hmmm, bad instruction? no parity in these machines, is there?
> something must be getting overwritten.

From what I've seen, machine check normally occurs when there is no
hardware set up to decode a particular address and a fetch or store
instruction occurs at that address.  At least that's the only time I
remember seeing it.  For example, between the I/O space of two motherboard
devices that aren't quite adjacent, or above the top of physical memory.

I've used machine check to probe to see if certain devices were there on
Nubus PowerMacs.  Read the version byte from the nubus controller.  If you
machine checked, surprise, you're a 6100 with no nubus adapter card....
:-)

Just my $0.02.


Later,
David

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