GTA04 Block V4

Werner Almesberger werner at
Fri May 2 03:43:53 CEST 2008

Carsten Haitzler wrote:
> pmu sequencing risk: as i understand it the pmu comes in a flavor that has its
> default exactly what we want.

I wish ... :-( It's merely the variant that combines availability with the
least evil set of default. Actually, I'm not even sure if we actually have
a choice among variants. If we do, it's not among many.

> so taking this into account, pmu has added to it the need to get a new
> toolchain working, a developer time to learn it and write code for it,
> for a new architecture and proprietary toolkit,

This is indeed one of the less pleasant aspects of this. I had a look
at several various low-end ARM microcontrollers, but they all tend to
be a bit on the power-hungry side, at least when compared to the MSP430.

The nicest one I found is the ST STM32F103 series, but they still eat
about 9mA at 8MHz (top speed is 72MHz, but then you need a crystal and
50mA), and 14uA in "Stop". (The low-power modes are similar to the big
ARMs, just the overhead is greatly reduced. Note that "Standby" here
loses the RAM content, so one has to use "Stop" to do something useful.)

A further disadvantage of picking such a chip is that we couldn't scale
down as far as with 8-bit or 16-bit microcontrollers. I.e., if we find
we only need very few features, the smallest member of the MSP430 family
comes in a 4x4mm package and costs below USD 1, while the smallest
STM32F103 would still be 6x6mm and cost more than USD 3.

Of course, it's a real ARM, with tons of peripherals, real JTAG, etc.

- Werner

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