Is GPIO1_3 special? was: figuring out which digital IO pins are unused

All of pins GPIO1_0:7 pins are working nicely for me now, with one exception:
GPIO1_3 complains that device or resource busy when I do

   echo 35 >/sys/class/gpio/export

This pin isn't differentiated from the others in GPIO1_0:7 the schematic or
system reference. Is there something different about it?


I guess I owe myself an apology. Please read section 7.2.1.

Everybody loves the beagles Gerald. So you shouldn't be owing
yourself an apology, since even if it was wrong to begin with nobody
would be offended. We're all grateful for your efforts.

What does 'cat /sys/kernel/debug/gpio' tell you?

Apparently this line:

    gpio-35 (w1 ) in hi

from `cat /sys/kernel/debug/gpio`

indicates that GPIO_3 is used by the 1-wire driver in the shipping
Angstrom distribution.


I can verify that. What you could do is re-compile the kernel without that particular driver, and free up the pin if you really need it.

– Stefan