[Fpga-synth] ARM FPGA Audio board assembled, test code working

[Theo Verelst]

On Fri, 2009-02-27 at 08:48 -0700, Eric Brombaugh wrote:
> I've got some updated information, including a photo of the completed 
> board, the source for the bootloader, base firmware and test FPGA 
> design. So far everything is working just as I had hoped - no cuts or 
> jumpers and the firmware is coming together without any kludges.
> 
> http://members.cox.net/ebrombaugh1/synth/armfpga/index.html
> 
> Now I have to choose the first interesting thing to do with it from the 
> long list I've made. :)
> 
> Eric


Hi,

With some interest I've read about a handful of designs on this channel,
I notice you've used a microcontroller: is there a reason for this, like
being used to it, I mean, an FPGA can hold one easily (albeit some are
licensed) or you could use a more powerful device like a DSP or maybe an
OMAP (combined dsp/mc) while you're at it anyhow to make a small track
PCB?

I've a combined Spartan-3 + Analog Devices DSP board design lying around
already for years which can transfer up to 40 Megabytes/Sec over a self
made bus connection from a dual core Blackfin (500 MHz) to a Xilinx FPGA
with a number of memory mapped direct communication registers. Would
that be an interesting contstruction to use as audio/synthesizer
processing basis? The DSP development boards have excellent 24 but AD/DA
converters, and I've well working synthesizer code with midi input
running on a simular DSP (same C development env) based on fast DSP
interupt routine simulating an analog synthesizer, which currently
interfaces with a CPLD (a small size programmable logic option), this
could easily be exchanged with a spartan board I have, or I could make a
new setup where most processing happens on the FPGA (like the Digilent
spartan 3e board Scott Gravenhorst uses, too) and let the DSP do only
some hard things like computing sines and division in C and DA (and AD
as I use for effects) too.

When making an FPGA synthesizer I suppose it is important to have an
idea of what type of synthesis is happening on it, what are you planning
to use as synthesis method? Virtual analog, FM, sampling, a hybrid form,
wavetable, additive, or ..?

The fun of the fpga in the synthesis is pretty much small granularity
computations per second is possible, so I'm curious to know what people
do with it, the techniques are readily available in all kinds of forms
but getting a good and competitive logic design from idea to logic
source to working FPGA is quite something, harder than programming the
next comparable micro-controller, of course.

I mean it's nice to play Moog as a hobby by planning a cabinet
(enclosure) with 20 jack holes in it and some potmeters and think about
what that could do as a syntesizer but it's even more exciting to make a
generator pcb work, or a filter!

Greetings,

   Theo Verelst
   http://www.theover.org/Synth