> Can I set some firmware variable to just make it boot?

per irix, you want some or all of these prom vars:

AutoLoad	Yes	boot automatically after reset/power?
autopower	y	if capable, powerup when power applied?
rebound		y	reboot after kernel panic?
ec0mode			for o2, force negotiation (10, 100, f10, f100)
SystemPartition		eg, scsi(0)disk(1)rdisk(0)partition(8)
OSLoadPartition		eg, scsi(0)disk(1)rdisk(0)partition(0)
OSLoader		eg, aoutboot
OSLoadFilename		eg, /vmunix