Working with the Beaglebone can be really frustrating. There are a lot of buggy libraries and incomplete docs, and the Sitara chip is really complicated, overloading its pins to do lots of different things.
Today I needed 8 GPIO pins for a test harness. I looked at the diagrams for the P8 and P9 headers and picked some likely-looking pins. I used the Adafruit_BBIO python library and set them up as outputs, then toggled them and watched with the meter. Three of them didn't work.
So I changed my script to try to toggle *all* the pins on P9, even the ground and VCC pins. Of course this doesn't bother Adafruit_BBIO because it has no error checking (ugh). Here are the pins that worked as GPIO outputs.
Note that this is from my Beaglebone *Green*. On the Beaglebone *Black* you'd probably need to disable HDMI for some of these pins to work.
Beware: I repeated this test several times across reboot and power down, and some of the pins worked the second or third time that didn't work the first. It's possible that's sloppiness on my part, but my intuition says no, and that Adafruit_BBIO isn't initializing the pins correctly, so there's some random chance at play. The best reference I've found so far in how stuff actually works is "Exploring Beaglebone", which is unfortunately a non-free book, but very well written.
P8_7
P8_8
P8_9
P8_10
P8_11
P8_12
P8_13
P8_14
P8_15
P8_16
P8_17
P8_18
P8_19
P8_26
P8_27
P8_28
P8_29
P8_30
P8_31
P8_32
P8_33
P8_34
P8_35
P8_36
P8_37
P8_38
P8_39
P8_40
P8_41
P8_42
P8_43
P8_44
P8_45
P9_11
P9_12
P9_13
P9_14
P9_15
P9_16
P9_23
P9_24
P9_25
P9_26
P9_27
P9_28
P9_29
P9_30
P9_31
P9_41
P9_42
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