360/30 in FPGA (Was: Re: photos from VCF UK)

Lawrence Wilkinson ljw-cctech at ljw.me.uk
Wed Jun 30 17:10:58 CDT 2010

On Mon, 2010-06-21 at 20:46 +0100, Lawrence Wilkinson wrote:
> On Mon, 2010-06-21 at 14:25 -0400, Dave McGuire wrote:
> > On 6/21/10 7:03 AM, Roger Pugh wrote:
> > > I quite fancy an IBM 360 / 30 FPGA board now i know a little about big
> > > iron!
> > 
> >   Urr?  Is someone working on that?
> Ah, yes.  VCF was its debut.  I haven't got a page up yet, but you can
> see Andrew's photo at:
> http://www.flickr.com/photos/carrierdetect/4718559358/
> Basically, it's a 1000K gate Spartan 3 which contains the microcode
> store (2k x 55) and 8k x 9 of main memory.  Front panel switches are
> physical rotaries and pushbuttons; blinkenlights are via a VGA display
> for now.
> Right now it fails the microcode startup diagnostics with a main memory
> parity error, probably due to a race condition somewhere (the
> memory /used/ to work).
Ok, diagnostics complete ok and I'm on to getting it to run a program.
Basic execution and single-instruction-stepping works.  Just fixed a
VHDL problem related to RX opcode handling, but from now on the majority
of problems are likely to be microcode-related.

The main memory problem turned out to be the main clock too slow by a
factor of 4.  The memory runs asynchronously relative to the CPU, and it
had the correct timing, so it was effectively responding in a quarter of
the normal access time which messed things up.  Happy Happy Joy Joy.

If anyone has a Digilent Spartan3 board and would like to play with it,
I can try to come up with a configuration that will work without
external switches.  You won't be able to do much!

Lawrence Wilkinson                                 lawrence at ljw.me.uk
The IBM 360/30 page                       http://www.ljw.me.uk/ibm360

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