[sdiy] FPGAs

[Neil Johnson]

Hi Matthew,

> I've ordered the following through Abebooks:

There are some more recommendations here:

http://www.fpga.synth.net/books/

That site in general is a good intro to FPGAs for synth designs:

http://www.fpga.synth.net/

> 1) Development environment must work under Linux. Preferably *any* Linux (I
> run 64 bit Debian Lenny on all my machines) but I can always run a virtual
> machine under VirtualBox, if necessary.

For the design stage I recommend Icarus Verilog and GTKWave - used
them for years.  Both are available as packages for Lenny.  I've tried
using the simulators in the Lattice, Xilinx and Altera tool sets, and
so far have stuck with Icarus and GTKWave - so much faster and so far
hasn't crashed or hung (unlike Xilinx for example....).

And a lot smaller than 3+GB!!

The only time I fire up the Xilinx software is for the final stages of
targeting a specific device (place and route, timing analysis,
bitstream generation).  By that stage a lot of the logic functionality
is simulated and checked correct, so there's less work to be done.

> 2) Cost - I want to find a device that is affordable which I can programme
> with tools that are also affordable (or free.)

For Xilinx:
- devices are very competitively priced

- tools are free to download, and support Verilog (yeah!), VHDL
(booo!) and schematic (good for top-level block diagrams)

- you can get the schematics for a parallel port programmer from the
Xilinx website (free)

- or you can buy cheap Chinese clones of the Xilinx USB programmer off eBay

- the Xilinx FPGAs are SRAM based, so need programming at power - can
either be done with an external serial or parallel flash, or from an
on-board micro (my preferred method).  Their CPLDs are FLASH based, so
only need programming once.

> Altera offers a Linux version of it's Quartus II software for free.

I only ever tried Altera stuff once....a long time ago.....  *shudder*

> Next cost issue is a programmer. I'm rather hoping that this is something
> that I can build myself, assuming I can find the appropriate application
> note giving the spec. (Based on my experience of microcontrollers.)

Xilinx has the schematic online.  Couldn't find any info for a Lattice
programmer :(
Although I have a few kicking around from past projects.

> 3) Physical device. Here's the crunch - I've got to be able to solder this
> thing to a hand-made board. Even if I get a board made by Futurlec, BGAs are
> *out*. I reckon I can solder a 144 pin QFP, but think that would be about my
> limit. I don't actually *need* lots of IO pins - so where's the 40-pin DIP
> version, guys? ;-)

I'm using a 50k-gate Spartan 3A FPGA in a synth project.  Not sure yet
if I can fit into the smaller VQ100 package or I need the extra IO in
the TQFP144.

You also need to consider how many power rails you're happy to
support.  Some FPGAs need 3 supply rails (3V3, 2V5, 1V2), others are
slightly more friendly with only two rails (3V3, 1V2).

As for BGA sockets... yes you can buy them.  But they're pricey.  Very pricey.

I've used all three families of devices professionally, and Lattice
and Xilinx at home.

Cheers,
Neil
-- 
http://www.njohnson.co.uk