Here are some information I could not find anywhere. I post them here
for future reference (you know, when you type "KGDB NetBSD macppc" on
Google and you get what you are looking for :o)

The KDBG lines in GENERIC are revelant only if you have a serial port on
a PCI board. If you use the built-in serial, you need:

options KGDB
options KGDB_DEVNAME="ttya"

Speed seems hardcoded at 19200 bps. I could not change it.

The ttya name is the OpenFirmware name of the serial port, it's not a
NetBSD device name. The default (if you ommit the line) is scca. The
OpenFirmware commande devalias will usually give you the serial port
name (along with various other names, you've got to pick up the right
one).

And rebooting the remote machine after modifying /etc/ttys seems
mandatory. Probably a bug in our init...

-- 
Emmanuel Dreyfus
Il y a 10 sortes de personnes dans le monde: ceux qui comprennent 
le binaire et ceux qui ne le comprennent pas.
manu@netbsd.org