Debugging kernel over serial console?

[Ed Carp]

We're doing a port of both 2.0.30 and 2.2.14 to a, um, less-than-compliant PPC.
We're seeing Linux go out to lunch after about 3 weeks or so of operation.  I
talk to a terminal server that talks to the Linux box through the serial port,
so the usual way of doing things with shift/scroll-lock won't work.  Anyone have
an idea as to how I can debug this box? TIA :)