CPU selection

From: francesco (r.nospam_at_virgilio.it)
Date: 03/29/05 

Date: 29 Mar 2005 05:10:31 -0800

For a sensor application, I need to select a CPU able to:
- wake-up from power down;
- sample a sound signal for at least 20 sec;
- process the signal in time and frequency domain (at least, FIR and
FFT);
- send some result on a serial port;
- fall back to sleep for at least 2 min.

The application should be solar powered, so it need to be very very
low power.

I have considered some 8 bit processors, in particular Atmel
ATMega128L.
This processors offer very good power down current, but awful
processing performance. This means that, for instante, an FFT require
more time and, in consequence, more power.

Other choice: a low end DSP. I have considered:
- TI - TMS320C2407A;
- Analog Devices - ADSP21990;
- Microchip - D*** 30F3012;
First two DSPs offer a lot of processing power, but need about 200uA
in power down. Last one is, in a certain sense, a middle way.

Finally, I've considered a 32-bit processor: Intel PXA270 (Xscale).
Good processing, but it need a lot of power to enter and exit power
down. And it has a lot of useless peripheral which, in the end, use
power. Finally, von Neumann architecture should require bus
contemption between data and code, reducing power in respect of the
above illustrated DSPs.

I've made my mind to Texas Instruments, leaving a possibility for
Microchip.

Does anyone have any suggestion to give?
Does anyone know some benchmarks to consult (for example, how many
time is required for an FIR or an FFT on different platforms)?

Thanks a lot.
Best regard.

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