[sdiy] adding more audio inputs to the ATMEL AT91SAM7SE processor

[Eric Brombaugh]

Julian wrote:
> After all the talk of microprocessors recently, ive been looking more at 
> the ATMEL AT91SAM7SE ARM unit, as it looks like it has a good ammount of 
> fairly easily implamented I/O.
> 
> However, that said, i cant work out how easily to add more audio inputs.
> 
> Theres a paper ( 
> http://www.atmel.com/dyn/resources/prod_documents/doc6020.pdf ) that 
> shows connection of one or two of the SSC interfaces to an audio ADC, 
> but the example is just dealing with two inputs (stereo) whilst, 
> ideally, id like somthing to implament further inputs.
> 
> The datasheet for the device is availible from atmel (obviously) but 
> theres a copy here too ( http://www.farnell.com/datasheets/102193.pdf )
> 
> The reason why im looking at the 7SE variant over the 7S is in the hopes 
> of adding sample storage more easily.
> 
> As you may have guessed, im a novice at microprocessor implamentation, 
> but im trying to make a start : )

Yes - the Atmel SAM7 parts are fairly attractive MCUs. They've got some 
useful peripherals, a fair amount of I/O and are amazingly inexpensive. 
Digital Audio is handled via the SCC (synchronous communications 
controller) which can be configured for a variety of different serial 
audio protocols and has both input and output capability.

Adding more audio I/O will be a challenge though: The SCC is really only 
designed to handle a single I2S codec, which means you get two channels 
of input and two channels of output. To add more channels of I2S I/O 
you'll have to start hacking on your own hardware - either some kind of 
kludge to mux the single SCC port signals, or a complete separate 
interface. Neither of these is particularly attractive unless you have 
access to CPLDs and/or FPGAs.

A few other things to note:

- The SE parts are distinguished by having external memory access ports. 
This means they have a lot more I/O pins than the S parts which are 
completely self-contained. To handle all this I/O, they come in 128-pin 
LQFP and 144-ball BGA packages. I haven't done a search online to see if 
there are pre-built development boards available for these parts, but if 
not you may find this type of hardware construction to be a big 
challenge to take on.

- The external memory bus interface shares pins with GPIO and other 
peripherals. If you want to use external memory you'll find that the SCC 
I/O pins conflict with some of the address and chip select pins and will 
constrain the amount of external memory you can access.

If you're just interested in some fundamental concepts of 
microcontrollers and audio then the SAM7SE or SAM7S parts may be ideal 
places to start. If you have definite requirements for more than 2 
channels of processing and large external memories then you might want 
to consider looking at other architectures.

Eric