> Using the proprietary firmware for this would be ideal. It would also
> provide reliable access to the kernel debugger which would be
> extremely
> helpful for diagnosing what's going wrong with the console. I'm not
> sure how I would go about making progress on this though. I know there
> are binaries of the BIOS for Sun4m machines floating around but I'm
> not
> aware of any for Sun4u machines.
> 

I haven't been able to find any of this firmware either. Not sure if
this helps but someone says they've got the Ultra 1 firmware (along with
cgsix and cgthree) available here:
https://people.csail.mit.edu/fredette/tme/sun-u1-nbsd.html