Berndt Josef Wulf <wulf@dingo.ping.net.au>  wrote:
 > is there any reason why NetBSD-alpha goes into debug mode whenever it
 > looses connectivity to its serial console? I still haven't managed to
 > get one of my graphics cards, e.g. Diamond S3 Trio 64 and hence
 > still use the serial console. However, the kernel enters debug mode

"Doctor Doctor. It hurts when I do this."

I don't have an alpha, but this is the classic, age-old problem of 
serial consoles.  Sparcs have it too.  Some people claim you can 
make a dongle that pins dcd to dtr.  I personally think it has to do
with wiggling the cable to disconnect it and you're sending a long null
on the RX pin which looks like a <break>...

Try unplugging the other end first. That might help too.

Can you disable ddb with 'sysctl -w ddb.fromconsole=0'?

Anyway, this is not an alpha specific problem.