[sdiy] FPGA digital audio

[Grant Richter]

> To be proud to have designed & made everything from scratch, and to have
> a real application to explore and learn more about FPGA domain (which is what
> DIY is all about IMHO)...
> 
If anyone does get serious about doing an FPGA design. My buddy Nick Hartl
is the Xilinx field applications engineer (FAE) for the Chicago area. I
mentioned the idea to him and he has indicated he would help out when he
can. He's more into detectors for Fermi Lab, but he thinks the idea is
"quite doable". Gate delays are a uniform 1 nanosecond.

FPGAs are really large RAMs which do logic by look up tables. They are now
starting to get to the point where you an mix RAM and logic pretty easy (say
for a quadrature sine wave generator, a frequency shifter is something that
could be done in an FPGA). The strength is the software support and multiple
input formats (schematic, VHDL, others). There are some advantages over a
DSP approach unless you like to write software.

Some FPGA tips from him:

Convert all asynchronous signals to synchronous by registering at the input
pins.

Do a completely synchronous design using a single clock.

Always bring at least 4 or more pins to test points for internal probing
(you can route any signal to a test point to see if it is doing what you
think)

Don't hand route (except as a very last resort)