24 Sep
2001
24 Sep
'01
11:34 p.m.
On Mon, Sep 24, 2001 at 09:28:19PM -0700, Chris Kennedy wrote:
Derek Peschel wrote:
... And once you've loaded your own microcode, do the PROMs take up any
room in the microaddress space? And does the microcode handle the load
operation, or is there some sort of dedicated circuit?
I assume the load operation isn't supposed to happen while an ordinary
program is running (though that _would_ be an opportunity for spectacularly
efficient and inscrutable code).
It's scary how similar this is to a popular booting technique (switch on
boot ROM, use it to load RAM, switch off boot ROM) except, of course, that
you're one level lower.
-- Derek
But where is the microcode for the brain-damaged
Nova 800 instruction set
stored, and can it be overwritten?
PROMs, and no, I know of no way to overwrite _that_ code. Instead you
execute a load microstore operation, which moves data from memory to
microstore and resets the machine such that it begins execution from
soft microstore rather than the proms.