well in a drastic situation you could (with the kernel's namelist) drop
to the console and twiddle the right bits to jump yourself into ddb :-) 
it actually wouldnt be too hard. you might have to first look to see what
a normal entry to ddb would look like and fake that, build a stack frame
by hand and then set the pc, and then resume execution. 
of course, one annoying thing about the later DECstations is that the halts
and so on are done in software that for some reason seems less robust as 
each subsequent model came out, such that on the '240 and the '260 i have
encountered crashes in which the halt button did nothing. 

ymmv,
isildur

On Sun, 18 Nov 2001, Bob Lantz wrote:

> Arrgh. My DS5000/260 ran 1.4 flawlessly for nearly a year without
> rebooting. Since I upgraded (?) to 1.5.2, it has crashed four times -
> frozen completely. Each time, I can't enter DDB, so I have no idea:
> software crash? hardware failure? network problem? who knows?!!
> 
> Does anyone have any suggestions of how to get information out of a
> machine that is just sitting frozen? Is there any way to get into
> DDB even if you're blocked in some normally non-interruptible state?
> 
> I would just like to know what is going on...
> 
>