[sdiy] Freescale Soundbuite

[Eric Brombaugh]

On Feb 3, 2008, at 2:03 AM, Johannes Öberg wrote:
>> From the "which DSP should I choose" page I become suspicious the
> SoundBite cannot interface external memory. Are we stuck with 88k of
> internal RAM ?
>
> Any (as in *any*!) way around that? Have sort of a sampler-based synth
> project in mind and would prefer to have at least 256 kilowords of
> sample RAM.
>
> (I am not good with computer and can't figure it out from the  
> Freescale page)

88kB is the internal RAM. There are several schemes by which you can  
allocate it between program and data space, but that's all you get for  
direct access. If you want additional memory for sampling then your  
only option for this particular processor is to hook up an external RAM.

Since most of the DSP56371 I/O pins are already committed on the  
SoundBite board,  that means you'll have to warm up the soldering iron  
and start hacking. There isn't enough GPIO to use a parallel RAM chip  
though, so you'll either have to design a serial/parallel RAM  
controller, or you need to buy a serial RAM chip. Serial RAM is not  
very common, but you might be able to use FRAM which is a high  
endurance non-volatile technology that is available with SPI  
interface. Unfortunately, the sizes are somewhat limited (32kx8 max in  
DIY-compatible packages) so you'd need 16 of them for your target  
sample size, and at ~$5.00 each that's going to get expensive pretty  
quick.

It seems to me that if a sampler is what you're trying to do, the  
SoundBite really isn't the right platform to start with.  Any other  
microcontroller out there with a large GPIO complement would probably  
do - you can use ARM, PIC, AVR, dsPIC, etc, coupled with a good-sized  
parallel SRAM. For sampling you don't need a whole lot of DSP power  
either, so that opens up the field a lot. Or, try the Xilinx Spartan  
3e Starter kit - it's also only $150 and includes ADC/DAC, a huge  
DRAM, etc. There's even a sampler design available online for it  
already, which would give you a good start.

Eric