> My machine (IIcx, 20M RAM) has recently become quite unstable.

What have you changed?  Anything?

> When I reboot it
> after one of these hangs, it frequently complains that it can't
> initialize ae0 because it can't clear shared memory; could this
> be a clue?

I don't think so, but possibly...

> How can I get a backtrace (or other useful information) from the
> debugger?

"trace"  You can use "man ddb" for more info on ddb.  Of course, that
doesn't help when you need it the most, eh?  ;-)

-allen

-- 
Allen Briggs - end killing - allen.briggs@bev.net ** MacBSD == NetBSD/mac68k **
   Where does all my time go?  <a href="http://www.netbsd.org/">Guess.</a>