GPIOlib
From ArmadeusWiki
Contents
Introduction
With recent Linux kernel (> 2.6.3x), there is an abstraction layer meant to ease GPIO usage: gpiolib. We will explain here how to use it.
Installation
- Configure Linux kernel
$ make linux26-menuconfig
- Enable the sysfs interface of the GPIOlib If not already done:
Device Drivers --->
-*- GPIO Support --->
[*] /sys/class/gpio/... (sysfs interface)
- In order to test the GPIOlib with the user LED and SWITCH of the board you will have to disable the GPIO_keys and GPIO_LEDS drivers that are the regular driver for such device.
Device Drivers --->
Input device support --->
[*] Keyboards --->
< > GPIO Buttons (be sure GPIO Buttons is unchecked)
Device Drivers --->
[ ] LED Support ---> (be sure "LED Support" or "GPIO connected LEDs" (hereafter) is unchecked)
< > LED Support for GPIO connected LEDs
- Save your new configuration and rebuild your kernel (if needed)
$ make
- and reflash your kernel (if needed)
Usage
Blink APFxxDev i.MX LED
- Find the GPIO number connected to the LED, eg:
- for APF27Dev: PF14 -> PortF (n°6) pin 14 -> (6-1)*32 + 14 -> GPIO n°174
- for APF51Dev: GPIO1_2 -> Port 1 pin 2 -> GPIO n° 2
- for APF28Dev: Bank 0, pin 21 -> GPIO n° 21 (0*32 + 21)
- Define envt variable (for portability):
# export LED=174 (APF27Dev) or # export LED=2 (APF51Dev) or # export LED=21 (APF28Dev)
- Ask kernel to export the GPIO:
# echo $LED > /sys/class/gpio/export
- Access functions are created:
# ls /sys/class/gpio/gpio$LED/ active_low edge subsystem value direction power uevent
- Check GPIO direction and put in output:
# cat /sys/class/gpio/gpio$LED/direction in # echo out > /sys/class/gpio/gpio$LED/direction # cat /sys/class/gpio/gpio$LED/direction out
- Play with GPIO value to blink LED:
# echo 1 > /sys/class/gpio/gpio$LED/value # echo 0 > /sys/class/gpio/gpio$LED/value
Get APFxxDev i.MX switch status
- Find the GPIO number connected to the switch, eg:
- for APF27Dev: PF13 -> PortF (n°6) pin 13 -> (6-1)*32 + 13 -> GPIO n°173
- for APF51Dev: GPIO1_3 -> Port 1 pin 3 -> GPIO n°3 ((1-1)*32 + 3)
- for APF28Dev: Bank 0, pin 17 -> GPIO n° 17 (0*32 + 17)
- Define envt variable (for portability):
# export SWITCH=173 (APF27Dev) or # export SWITCH=3 (APF51Dev) or # export SWITCH=17 (APF28Dev)
- Ask kernel to export the GPIO:
# echo $SWITCH > /sys/class/gpio/export
- Access functions are created:
# ls /sys/class/gpio/gpio$SWITCH/ active_low edge subsystem value direction power uevent
- Check GPIO direction and put in output:
# cat /sys/class/gpio/gpio$SWITCH/direction in
- Get switch status:
# cat /sys/class/gpio/gpio$SWITCH/value 1 (released) ... # cat /sys/class/gpio/gpio$SWITCH/value 0 (pressed)
- Block until an event occur:
# cat /sys/class/gpio/gpio$SWITCH/edge none # echo both > /sys/class/gpio/gpio$SWITCH/edge
