GTA02 MPU alternatives

Werner Almesberger werner at
Sat Apr 26 00:19:50 CEST 2008

Ian Stirling wrote:
> Sorry.

It's me who has to apologize. When I read your mail, I got confused
and thought it came from Joerg. Since we had just been on the phone
merely minutes before, discussing the role of the MPU, and this didn't
fit anything we need, I was a lot more sarcastic than would have been
appropriate. So, sorry, this wasn't against you but against some
figment of my imagination :)

Our display will be attached to the 6400, which takes of frame timing
an all that, so it would be difficult for an external processor to do
something useful with the LCM, and it probably wouldn't help to save

We will actually have some dual-ported RAM there (not that we neeed
it, but this is the only multi-chip package available), so some
external processor could in theory access a frame buffer or similar

The 6400 has three SD/MMC channels, and we'll use one for WLAN and the
other for the microSD card, leaving one "unused". (The pins will be
available for GPIO, so they're not wasted.)

The main role we envision for the MPU is to act as a majordomo who
lives in a different power domain (hmm, what would J. M. Barrie have
made of this ? :) and who takes care of all the small tasks of running
the infrastructure we don't want the big CPU to worry about.

I posted my list of ARM-based not-really-alternatives to the TI MSP430
because it was suggested that we should use something that didn't need
a different cross-development environment. 

However, even though ARMs are starting to look better for tasks
traditionally the domain of 8 bit CPUs (surprisingly even in terms of
chip price, so whether we have an ancient 8 bit core or a modern 32
bit core doesn't seem to affect the cost very much anymore), they're
still not quite there when it comes to voltage range and ultra-low
power when idle.

- Werner

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