I've been trying to get input and output GPIOs to work following Derek Molloy's videos and book. I'm using Debian 7/3.8.13-bone68. Pin 36, by default, is configured as an input with pullup enabled. When I measure that pin with a DMM, it's near 3.3 V. But when I try to read the value via sysfs, I always get 0.
Here's how things look for pin 36, P8_07:
# cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pins | grep 890
pin 36 (44e10890) 00000037 pinctrl-single
# ls /sys/class/gpio
export gpio36 gpiochip0 gpiochip32 gpiochip64 gpiochip96 unexport
# cat /sys/class/gpio/gpio36/direction
# cat /sys/class/gpio/gpio36/value
# cat /sys/devices/bone_capemgr.9/slots
4: ff:P-O-L Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G
5: ff:P-O-L Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI
Similarly I tried setting the direction to "out", and tried setting the value, but it had no effect on the output voltage.
Am I missing a step? I followed the instructions here: http://derekmolloy.ie/gpios-on-the-beaglebone-black-using-device-tree-overlays/
I also tried setting up the overlay as directed later in the example, but it made no difference.
I'd really appreciate any help!