CD boot fails (Decrementer exception)

[Ross Gohlke]

Thanks for the suggestion. In the meantime, I downloaded a fresh bootonly
ISO from
freebsd.org and burned it on a friend's Windows XP box.
It boots per the instructions, but hangs for about 10 minutes:
acd0: TIMEOUT - READ_BIG retrying (1 retry left)
... variations of the above for about 12 lines

But it works!

> 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?

Yes, the loader got all the way to "hit [enter]" screen (I let it time
out). then gave the error, which changed to:
Invalid memory access at %SRR0: 0035fc04   %SRR1: 00002032

I'm not sure what happened to the CD since I burned it...

> 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
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