[sdiy] ARM based digital synth.

[Eric Brombaugh]

Alwyn Lloyd wrote:
> 
>> There are a lot of decent quality and inexpensive AC97 codecs available.
>> The big problem you'll run into is that you really can't bit-bang the
>> AC97 interface in software - you'll need some sort of customized
>> hardware to talk to it. Might I suggest an FPGA or CPLD?
> 
> I was hoping to keep it fairly simple and cheap, and im not sure i'd be
> quite up to designing something like that, though atmel have an apps note
> on a very similar thing as part of their arm notes.
> 
> What i have found out though is the phillips chip have 2 SPI ports, and
> can be run at a maximum of 1/8th of the clock rate.  which is fast.  I'm going
> to have a look at whether i2s and spi are close enough that one could use
> the spi ports as i2s ports.

Interesting idea. There was an article in the latest issue of Circuit 
Cellar that described an I2S port implemented on a TI DSP using a SPI 
port and some of the internal timers. You might be able to lash up 
something like that - sort of half software & half hardware.

> The aim is to try and make something thats fairly straightforward and
> simple to make.  The other thing is versitility.  All you need to do is
> make a new UI panel and connect it to the i2c bus, write some new software
> and you can have a different synth..

Interesting. The main problem is that I2C is somewhat slow. Did I see 
that Philips part has CAN bus on it too? How does that compare in speed 
to I2C? There's a guy around somewhere who's doing a synth system using 
CAN bus for all inter-module communication...

Eric