SD/MMC vs. GPS: drive strength ?

[Werner Almesberger]

I wrote:
> Please don't read too much into the little waves that ride on
> top of the curve. They're just ambient RF pollution.

Joerg suggested that this may be reflections. So I tried again with
a probe that's less noise-prone:

These two waves with maximum drive strength show a quiet moment ...

http://people.openmoko.org/werner/mmc_drive_max_quiet.png

... two noisier moments ...

http://people.openmoko.org/werner/mmc_drive_max_bounce3.png
http://people.openmoko.org/werner/mmc_drive_max_bounce4.png

... and a mixed result with minimum drive strength:

http://people.openmoko.org/werner/mmc_drive_min_both.png

Since the amplitude of that ~100MHz noise varies somewhat with the
drive strength, reflections seem to play a part. But most of it is
probably just FM radio I pick up.

The important bit is still that the clock edges change speed, which
can now be seen more clearly.

- Werner