[sdiy] Propeller chip from Parallax

[Scott Gravenhorst]

I've been working with FPGA's for about 9 months now, specifically the Xilinx Spartan-3E.
 Granted, the dev board is more than the price of the Propeller at $150.  The chip is
spec'd at 230 MHz max, on board system clock is 50 MHz (you can usually get 3 cascaded
multiplies done in one 50MHz clock cycle).  The chip has 20 multipliers (18x18 signed) in
it, and the board is loaded with other goodies.  

If you want parallelism and superior I/O capability, IMO, FPGA is the thing.  And like
the Propeller and/or AVR, it can be reprogrammed as often as you like.  The dev software
is free and the docs are, IMO, excellent.  See the Xilinx website for more details.

I'm currently near completion of a 4 NCO monosynth that started out as a digital
emulation of a FatMan, but it's gone well beyond that.  It currently has a built in
softcore MCU for MIDI, supports sysex parameter updates (14 bit parameter address space),
_digital_portamento_ (each NCO gets it's own portamento time), 4 waveforms (saw, tri, PWM
with routable modulation inputs and sine), global microtuning, microtuning per NCO,
coarse (semitone) tuning per NCO, master transpose, level control per NCO, IIR digital
filter, 2 ADSRs (NCA and NCF), pitchwheel, mod wheel, 2 axis joystick, velocity and
channel pressure.  The MCU code is currently 284 locations out of a possible 1024 so more
features can be packed in.

To say the least, this FPGA is awesome.  The GateMan-I project uses approximately 20% of
the chip (110,000 equivalent gate count).  To say the least, the chip is loafing.  Output
sample rate is 1 MHz so no anti-alias filter is necessary.  The design could handle 12
NCOs at this sample rate (and I'm not sure it's completely optimized).

The code will be posted as open source when It's finished to http://www.fpga.synth.net/

-- ScottG

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-- Someday is not on the calendar.

-- Scott Gravenhorst
-- Xilinx Spartan-3E Based Music Synthesizers
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/