When Linux is booted, there are several things allowing to control the hardware.
LED support must be enabled in the Kernel. Additional triggers can be appended by configuration at compilation time.
Initially, KizOS shows the status of the TaHoma using its 2 RGB LEDs. Once the regulator feeds the LEDs with the right voltage, they can be controlled using /sys/class/leds/pwm:<color>:user.
For example, setting the LEDs to green will look like something like:
echo 128 > /sys/class/leds/pwm:green:user/brightness
echo 0 > /sys/class/leds/pwm:red:user/brightness
echo 0 > /sys/class/leds/pwm:blue:user/brightnessThe brightness can be adjusted between 0 and 255.
At start, the USB-A port is disabled. To enable it, it is necessary to set the GPIO PE3 to HIGH first.
To enable it, we need to take 2 steps:
- Export the pin
- Set the pin to output and the level to high
In Shell this gives (note that this won't work with Linux <= 3.7):
PIN=131 # 131 is PE3's pin number
NAME=pioE3 # pioE3 is PE3 full name
VALUE=1 # Value is high for bus powering
# If the pioE3 GPIO is not already exported
if ! test -d /sys/class/gpio/$NAME ; then
echo $PIN > /sys/class/gpio/export
fi
# Set the pin as output and set the value
echo out > /sys/class/gpio/$NAME/direction
echo $VALUE > /sys/class/gpio/$NAME/value