CD boot fails (Decrementer exception)

[Philip Schulz]

2008/7/8 Ross Gohlke <ross at grinz.com>:
> I am finally getting around to the Xserve installation I asked about
> previously:
> FreeBSD 7.0-RELEASE installer CD (burned on an iBook a month ago)
> Xserve G4 Dual 1GHz
> Following these instructions:
> http://people.freebsd.org/~grehan/iso_install.txt
>
> Boot holding down 'c' does not work.
> Boot into Open Firmware (hold down Cmd-Opt-o-f) and issue:
> 0 > boot cd:,\boot\loader cd:0
>
> OF finishes loading, then reports:
> Decrementer exception at %SRR0: 0035fc04   %SRR1: 00002032
>  ok
> 0 >
>

Does the loader start at all?

I haven't experienced the issue myself, but I think what happens is
that Open Firmware enables interrupts before the kernel has a chance
to install its own exception handlers. I have seen reports that the
exception occurs both on NetBSD and OpenBSD. The latter seems to have
added a workaround: They set the decrementer register to a very high
value, very early in the boot process (possibly even in their loader).

You can accomplish the same from Open Firmware:

> 1 1f lshift not dec!

This should set the decrementer register to 0x7fffffff which is the
highest possible value. This should give you enough time to execute
the loader and start the kernel.

You could also try and start the kernel directly, without the loader.

HTH,

Philip