[rescue] 3b2 Emulator

[Jerry Kemp]

FYI.

This isn't mine, and I don't have any insights into this aside from the post.

This is a repost of an email from the Classic CMP mailing list dated 19 January 
2015.

I thought that it might be of value as we have a 3b2 discussion ongoing at that 
time.

Jerry


P.S. Mr. Bill, hope your job search is going well!
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Hi everyone,

I've made tremendous progress on my 3B2 emulator. It's being
implemented under the SIMH simulator platform, which has been a huge
help.

My WE32100 core is getting closer to being complete. I'd consider it
alpha quality right now, but it has enough instruction coverage to
pass the 3B2's power-on self tests and to (barely) run some of the 3B2
firmware mode tools.

Implementing the WE32100 core has been thanks to the processor manual
and assembly language manuals that are available on BitSavers, but
outside of the CPU, virtually all of my understanding of the 3B2's
architecture has come from studying the ROMs and the SYSVR3 source
code. I've also been helped by having remote access to a running 3B2
so I can assemble and disassemble code using the real AT&T tools.
Beyond that, I have found precious little documentation.

I'm at the point now where I'm pretty well stuck until I can find more
information. I understand large chunks of the memory map now and
should be able to do things like simulate the floppy and hard disk
controller, but there are large gaps in my understanding. There are
many undocumented registers that are used by the firmware, but don't
appear in the SYSV source code anywhere. What they mean and what
they're for is anybody's guess. I've just stubbed them out for now.

If anybody has access to schematics, architecture docs, or other
memory map information, I'd be eternally grateful if you could share
it!

-Seth