[sdiy] The Owl: ARM fx pedal

[rsdio at sounds.wa.com]

On Apr 24, 2013, at 20:43, Terry Shultz wrote:
> Let's review some facts to consider for Open Source based projects.
>
> Tools:
> Debugging JTAG tools, FTDI have some parts that could be used to  
> build up JTAG interfaces. Perhaps an open source debugger / JTAG  
> chain?

Dangerous Prototypes has an impressive collection of open hardware /  
open firmware designs. Their JTAG debugger is the Bus Blaster.

http://dangerousprototypes.com/docs/Bus_Blaster

I had already purchased a couple of commercial JTAG debuggers before  
they designed this at Dangerous Prototypes, so I have not used this  
particular one myself. However, I have used the Dangerous Prototypes  
Bus Pirate and Gadget Factory / Open Bench Logic Sniffer. It's great  
to be able to help design improvements to the hardware and firmware  
for these tools. Highly recommended!

> Hardware:
>
>  the ToneCore pedal could be retasked to use a Cortex M4. Currently  
> it uses a Freescale 9S08J64 for USB/ MCU and a DSP56364 for DSP  
> functions. I have a good deal of the original material and we might  
> be able to get Marcus Ryle to sell us some Tone core kits to retask  
> to our needs. I'll send him a note and see what he says and get  
> back to this list.

Do you mean retask the ToneCore pedal mechanical hardware? I assume  
that the CPU would be entirely different for a new project, and thus  
the existing circuit boards would be tossed.

> Dr. Beckmann has built up some great tools and perhaps a version  
> could be crafted to be made available at a reduced price.
> Dr. Beckmann was correct to suggest 44.1 KHz as a target frequency.

Forgive my present ignorance, but who is this Dr. Beckmann? Not the  
cleaning fluid brand...
I suggest 48 kHz because it is easier to get that frequency by simple  
division of standard clock crystal frequencies. Designs become more  
complex when you need two crystals. An fx pedal probably won't have  
digital I/O anyway, so it could operate at 50 kHz or 60 kHz, making  
the anti-aliasing and reconstruction filters a bit simpler and cheaper.

> What about a Stereo In and Out like the ToneCore unit?

Great idea. I like that the ToneCore also supports mono, and even has  
a way for the CPU to detect whether it is being used in a stereo or  
mono situation. Many vocal and guitar effects will be at least mono  
input, if not also mono output.

> General Midi could be supported via the USB and for software  
> flashing into the memory.

I do not understand the link you seem to be making between General  
MIDI and software memory. Are you talking about MIDI System Exclusive  
for transfer of data? USB-MIDI is probably a good idea, if it doesn't  
add significantly to the cost.

> I was plagued with calls on how to debug the DSP code and so on.  
> Not a good place to start a Pedal Open source project.
>
> Terry Shultz
> DSP and ARM Audio Technology and Applications
> thx1138 at earthlink.net

Again, forgive my ignorance: Did you work on ToneCore? What sorts of  
support calls were you getting about DSP, and in what context?

Brian Willoughby
Sound Consulting