FPGA VAX update

[Allison]

>
>Subject: Re: FPGA VAX update
>   From: Johnny Billquist <bqt at Update.UU.SE>
>   Date: Tue, 25 Oct 2005 15:38:27 +0200 (CEST)
>     To: cctalk at classiccmp.org
>
>On Tue, 25 Oct 2005, Ken Seefried <ken at seefried.com> wrote:
>
>> From: Johnny Billquist <bqt at Update.UU.SE>
>> > I think I have the documentation for the microcode for
>> > the different engines, and I also have the binary microcode
>> > files...
>>
>> Do you have the microcode files for the 11/730?
>
>Might still have the TU58 tapes around, yes. No TU58 drive to read them,
>though.

I must be thee rare one that maintaines TU58s for use.

>
>> The Am2901 VHDL (and other formats) is freely availible and well
>> understood and fits several to an FPGA (even small ones covered by free
>> tools).  The rest of the logic on an 11/730 CPU isn't that terrible
>> complicated.  Given access to the microcode, I'd imagine it would be a
>> reasonable project to whip up an ersatz 11/730, validate that it works
>> correctly, then proceed to optimize and otherwise improve the design
>> (add in pipelining, test, add in FPU, test, add in cache, test, migrate
>> to faster FPGA family, test).  Iterative, rather than shooting the moon
>> first run.
>
>Maybe. I think that there is probably a lot more logic outside the 2901
>than inside... We're still talking several boards of logic here... I doubt
>all of that is microcode memory, 2901s and 74xx series stuff. :-)

Bet on it as the 2901 only provides 16 registers and  I think VAX had more.
It's also a slow device. 

>> You could even short-cut some of the FPGA work.  I don't recall what
>> the microsequencer looks like on the 11/730, but if it's the usual
>> Am29{09,10,11}, there is at least one shop that still (as of at least
>> last year) makes an 8 x Am2901 + sequencer single chip ASIC that runs at
>> something like 20MHz.  Or you can find NOS for the IDT 49c402 that is 4
>> x Am2901s.
>>
>> This way of thinking won't result in the fastest VAX possible, but I
>> venture it has a better chance of resulting in an actual working VAX.
>
>It might be a possiblity. Not that I'll do it. But if someone really
>wanted this to happen, it's one possibility. Might be easier to talk with
>someone who still have an 11/730 running, to read his tapes though.

Not I.  I must ahve at least 16 2901C and 2911 and they are not that pretty
without a lot of glue.  More correctly, for some archetectures it's ugly
and for some a very easy set of peices to use.  The biggest problem is 
multiplexed external busses and that does impact design and speed.


Allison