7 Aug
2006
7 Aug
'06
3:12 p.m.
Tony Duell wrote:
Such CPUs may not be _made_ now, but this is the classiccmp list. I would
guess that many of the regulars here have at least one processor built
That very much depends on the CPU. If the CPU is
many chips (not a single
package) with microcode in PROMs, there's nothing to stop you desoldering
said PROMs and reading them out. I've done that, then written a
disassembler for the microode instructions and worked out what was going on.
True, but you don't find CPU's made of discrete logic these days, so
it
makes it very difficult to get at the microcode. from simple logic chips.
I am trying to think how many I have. It's going to be at least 20.
And some CPUs,
the PERQ being probably the most common example, load
their microcode from disk at power-on. In which case you might even get a
mcirocode assembler and disassember as standard OS tools. If not, you can
write them.
This is one machine I've been wishing for, for quite some time.
Were there any emulators of these? Are there enough docs,
schematics and
copies of the software online somewhere? Would be sad to lose this
Yes. Known to exist are schematics for all models apart from the T4 (I
must trace them out one day). Most are on bitsavers (I don't think the 3a
(AGW3300) disagrams are there, the only known set is reverse-engineered
anyway. And this machine isn't a classic PERQ, it's a 68020-based unix
workstation, albeit with an itneresting graphics processor). Those
scheamtics should be fairly complete. I have some bits not in the offical
books, like diagrams for the keyboards, monitors, disk drives, even some PSUs
PROM/PAL dumps (and equations for the latter) exist for all known PERQs
(including the T4). I think the only thing I don't have are the modified
programemd chips for the ST506 disk Interface board (DIB). I have the
ones for the normal ST412-compatible DIB, but there was apparently a
modified board to use with real ST506. I've never seen it, don't have
any details of the changes.
machine to the ravages of time.
I don't think that will happen. There are some serious PERQ-fanatics out
there.
This is rather
a higher level tham I was considering it. I was thinking
more along the lines of 'Decoder U55 decodes the 3-bit field consisting
of micorocode bits 23-25. Output 4 of this decoder enables OR gate U27c
which passes the delayed clock to the clock input of the D-type U71a.
This stores the carry output of the ALU, and acts as a carry flag'
Yes, I do often consider CPUs at that level
Wow. You da man! ;-) Sweet! Reminds me of the Xerox Star where it uses an
8085 to load code
into a custom made bit-sliced microcoded CPU, and even allows individual
applications to roll their own microcode...
Not suprising. There are many similarities between the Xerox workstations
and the PERQ. The fact that Brian Rosen worked on both may have something
to do with it :-)
But there are also differences. The PERQ's I/O processor (a Z80) most
certainly does not load the CPU control store. And having compared the
designs of the PERQ and the Xerox Daybreak (the only D-machine I've been
lucky enough to find), I will say I think the PERQ is the much better
design.
-tony