Looking at the output you see, I have doubts that it has anything to
do with SILO though. SILO prints letters 'S', 'I', 'L' and 'O'
(appearing before the prompt) after it completes execution of
different parts of first-stage loader. As you can see in the code
(first/first.S), printing 'S' is the first thing first-stage loader
does upon startup. The fact that it is not seen in the console output
suggests that even first-stage loader never got to run. The line
Boot device: /pci@1f,0/pci@1/scsi@8/disk@0,0:a File and args:
which is normally printed by OBP before control is passed to SILO does
not appear in the watchdog-reset case either, which, again, is a
strong sign that failure happens before SILO has a chance to run.