GPIO0 trough 2 shorted to ground

Werner Almesberger werner at
Fri Feb 22 13:34:35 CET 2008

When playing with the "gpio" tool, I noticed that the GPIOs driving
the LED transistors are effectively shorted to ground.

This causes a few curious effects, for instance that the pins read
back as zero even if set to one. This in turn means that the usual
way of modifying bits, e.g.,

gpiob |= 1;

will clear all the LED GPIOs that are not explicitly set by it.
This shows by the corresponding u-boot command acting strangely.
(So anyone testing the LEDs with u-boot should be aware of this

I'm not sure if all this causes any real problems (except for
drawing a lot of current, e.g., about 50mA per lit LED instead
of roughly 10mA, bringing idle current from ~120mA without LEDs
to ~265mA with all three LEDs lit), but it's certainly not pretty.

- Werner

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