GTA02 MPU alternatives

andrzej zaborowski balrogg at
Sun Apr 27 15:46:22 CEST 2008

On 26/04/2008, Werner Almesberger <werner at> wrote:
> 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
>  power.
>  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
>  there.
>  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.

Just a note: the Luminary Micro ARM Cortex one, not the same model but
near, even has emulation in qemu. It's also said to be $1 a piece -
dunno about power usage.

BTW. I note the 6400 for CPU has been decided on. Was the earlier
prerequisite of datasheet redistribution rights dropped or are we now
quite sure we will have this right? As was noted on IRC a late change
of the CPU won't be good because it's...well, the CPU.

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