[rescue] sun 3/60 update

[Romain Dolbeau]

Le mar. 27 mai 2025 à 05:35, Dan Moisa via rescue <rescue at sunhelp.org> a écrit :
> Alright folks here it is, courtesy of long weekend:
> https://github.com/54weasels/sun3_60/

Thank you so much for sharing this!

Somehow, seeing the schematics in modern Kicad makes it feel even more
complex and daunting than the original drawings... it's no longer
possible to blame bad readability. incredible work to replicate those
so nicely!

I'd never realized that the "Sun-style" MMU on those machines was done
in discrete logic and PALs... somehow from all the '030-era systems
with gate-array custom chips, I expected to see that and wondered
where you sourced them from... I understand now why they chose to do
the sun3x for the '030 and use the built-in MMU - cheaper and smaller
than having all of that on the board.

That's a lot of PALs to program, as well. I was wondering about
consolidating, but one of the links you have for the 3/60 mentions
some timing issues for the PAL used in the DRAM refresh circuitry :-(
Isn't the rare PAL8L14 just combinatorial ? At some real estate cost,
it could be replaced by a pair of smaller PALs, couldn't it? (if it
had registers, those many outputs might have dependency on one
another, but not in a purely combinatorial PAL if I understand PAL
equations correctly). That would double the load on the input lines,
but I presume (quite ignorantly) that by replacing them with modern
GAL the issue is mitigated. Also, it doesn't seem to have been
decompiled in the PAL directory, is that an oversight or is there some
issue that makes it impossible to do?

It's a shame 5V stuff is disappearing, and some massively popular
chips are no longer made. Even the ubiquitous Z8530 was retired
recently :-( Maintaining/making more of those is going to get harder
and harder. I wonder how you did manage to source all that stuff, some
seems to be quite rare (e.g. LS2518).

Cordially,

-- 
Romain Dolbeau