I'm not exactly sure when this stopped working...

# uname -a
NetBSD too.crufty.net 1.5ZA NetBSD 1.5ZA (TOO) #0: Tue Jan  1 03:00:52 PST 2002     root@too.crufty.net:/l0/sys/compile/TOO sparc

This is an SS20 with serial console.

During initialization, BREAK drops me to the prom's ok prompt.

Once the kernel has started booting though, BREAK is ignored.
My normal kernel does not have either of DDB or KGDB defined.
From dmesg.boot:

zstty0 at zs0 channel 0 (console i/o)

suggests that zs is being used for the console.  Here I see zs_abort()
which looks like it should end up calling prom_abort, but I don't see
where zs_abort is hooked in.

If I'm off track, a pointer would be appreciated.

Thanks
--sjg