GTA04 Block V4 / risk and possibility

Werner Almesberger werner at
Fri May 2 00:34:28 CEST 2008

Andy Green wrote:
> Werner and I often find something to disagree about, but in this case it
> seems we both are interested in how we can leverage a small supervisor
> MPU in this design.

Indeed. What I think confuses the issue is that the MPU for the
prototype ended up being pretty large, in terms of cost, storage it
provides, and also physical size.

I started thinking about having such an MPU in November, when we hit
some glue logic issue in HXD8, and I had some longing thoughts again
when we hit the HDQ timing requirements. My idea was to get something
in a 4x4mm package with ~8-15 usable GPIOs.

Unless we go too crazy with LEDs and buttons, I would still expect to
end up in about that range. However, I agree that, during development,
having a larger chip that already taps into everything can help us
avoid having to do an extra board spin if we encounter something we
haven't thought of before.

By the way, you saved us from disaster in the HDQ case by using FIQ.
Now Mike found the GSM UART overrun problems, and it seems that the
solution will require FIQ sharing, adding complexity and potentially
cases where conflicts can't be resolved.

The MPU gives us more chances to dodge this kind of bullets,
particularly if we discover them before we go MP ;-)

- Werner

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