[cctalk] Dumping an UV PROM for a Sun 386i

[Christopher Zach via cctalk]

Hi all!

I'm working on a little side project to see why one can't put a better 
CPU chip into a Sun 386i. Basically with a real 386 in the socket the 
system will at least start to flash the LEDs on the back, but with a 
Cyrix chip the LEDs are frozen on.

I can remove the frame buffer, memory cards, even the Timekeeper chip 
and I still see this behavior. Running with no CPU or no PROM chip makes 
the system flash no lights, pointing to the problem being code in the PROM.

Now, 386 CPUs don't have the CPUID register, but they do have a little 
feature where upon reset EDX contains a "3" to show the CPU "type". On a 
Cyrix chip it contains a "4".

My guess is the ROM code has at the beginning a check of EDX and if <>3 
go to a halt. I'd like to dump the code, find that check, and either 
replace the 3 with a 4, or replace the first HALT with a NOOP.

The PROM is an Intel D27010 which is an Intel 128k*8 chip. Unfortunately 
I'm not finding much in terms of either datasheets or PROM programmers.

Does anyone know how to/have the tools to dump and reprogram this? I'll 
bet the old archives that talk about the "Blue Lightning 386" working 
for boot were due to the chip being made under license of Intel thus 
being allowed to have that "3" in there.

But since I also have a TI 386/486 chip with 8k of L1 cache, a 486 core 
instruction set, faster multiplier, and clock doubling by default I 
think it might wind up being.... faster.

C