[sdiy] uC with mul

[Brock Russell]

> > > I might be wrong but I had the feeling that a 16x16 multiplier was a more
> > > attractive solution, or at least featured the right balance between type
> > of
> > > package, ease of implementation etc in a DIY context... Haven't checked
> > > the price yet though...
> >
> > I would go for a small FPGA, I mean if you didnt want a multiplier, you
> > could reconfigure it do other stuff at a later date
>
>Indeed. I'd go for the Spartran-II family. Cheap and capable. If you
>don't need much speed you can set up the multiplication as a
>shift-and-add thing. That becomes very size-efficient.

I agree. I've been doing Spartan-II designs for a year now. Amazingly
cheap, about $21 per chip in single lot quantities for an XC2S150-208,
a 150K gate device with 140 usable I/O pins. A 16x16 multiplier would
not use 1% of the device (except for I/O) and you can easily run them
at 200+ MHz internally.

Something like Jim's 18MHz top octave generator that he was trying to
put in an XC4003 takes up 3 or 6% of an XC2S150, depending which
metric you measure with, flip-flops or CLBs. There are some possibilities
here...

>What one really should have is a configurable MPU model which you can
>trim some depending on your needs and you toss in the various glue
>stuff as needed. A simple MPU model should be simple enougth to fit
>into a corner.

There is a Xilinx macro freely available that is an 8 bit microcontroller.
Check out http://www.xilinx.com/xapp/xapp213.pdf the KCPSM,
Constant(k) Coded Programmable State Machine. It can be used in
the Spartan-II and Virtex devices. The main limitation is only 256
instruction spaces, 512 if you work at it, although the recommendation
is that if you need more program memory just add another macro.

>There are people doing things like this and there is nowdays alot of
>code just lying around on the web waiting for someone to pick it up
>and use it. You can download tools of the web and chips are cheap - go
>for it ;O)

The Xilinx WebPack tools are free! I have had some trouble with them
but the latest version is much better than what was available a year ago
and the documentation is improving. The new tools also support
schematic entry. I find it more frustrating to use than VHDL but it does
allow one to implement designs without knowing VHDL or Verilog.

The Spartan-II eval board from Insight is $125 populated with an
XC2S100-208. I think it is $100 without the FPGA so you can add
any device you want in a 208 pin QFP.

>I thing many people try to solve things with MPUs just because they
>are there. Over in the logic corner many people try to solve
>everything in straigth FPGA. I think one can find an very fruitfull
>mixture in the mold between these areas.
>
>Cheers,
>Magnus - just nuts

Once again I concur. 12 years ago I was using 8051/DS2250's with
XC2064's and XC2018's now AVR's and 586's with Spartan-II's.
Micros and FPGA's are definitely complementary technologies,
just look at the Atmel FPSLIC. The only problem with them is the
cost - both tools and parts - but they are great devices.

Brock