How do I kill the console? (or how to make nullconsole work)

[John Pettitt]

I'm running 5.4 BETA1 on a soekris 4801 board.  The unit emulates a
console on a serial port.  I want to use the serial port for my GPS so I
want the console messages from BSD to go away - an in particular I want
BSD to ignore inbound data during the boot process.

So far:

I've used the regular mbr so that I don't get the disk prompt
I've added "boot" to loader.rc before the beastie call so that it
doesn't display the menu

Both these change work

However if I add boot.config with -n -m the system doesn't boot (and I
can't tell why because I have no messages!)
If I set console="nullconsole" the system doesn't boot and again I can't
see why.

Does anybody have any wisdom on how to get nullconsole to work?

John