How to use GPIOs

Overview

This How-To is meant to be a starting point for people to learn use GPIOs for IGEP devices as quickly and easily as possible.

There are more ways to use GPIOs. This article show two simple ways to use gpios: bash commandline and C-code.

For this How-To I used IGEP firmware Yocto

Feedback and Contributing

At any point, if you see a mistake you can contribute to this How-To. Edit yourself !

Requirements

For this How-to, I used:

• IGEPv2 Board
• Only for C-program example it also needed:
  • Add shortcircuit cable between J990:20 and J990:22 pins. By default, GPIO 156 (J990:20) and GPIO 157 (J990:22) are available on these J990 pins.
  • GPIO example

Bash commandline

Basic gpio operations could be done using bash and sysfs :

• Export GPIOs

  echo "GPIO number NN" > /sys/class/gpio/export

• Unexport GPIOs

  echo "GPIO number NN" > /sys/class/gpio/unexport

• Set GPIO direction

  echo "out" > /sys/class/gpio/gpioNN/direction

• Set GPIO value

  echo "1" > /sys/class/gpio/gpioNN/value

• Get GPIO value

  cat /sys/class/gpio/gpioNN/value

• Configure hardware interrupts

  echo "rising" > /sys/class/gpio/gpioNN/edge

C-program Example

C-program Example contains some C-functions to control GPIOs. These also can do:

• Export and unexport GPIOs
• Set GPIO direction
• Set GPIO value
• Get GPIO value
• Configure hardware interrupts

Example program configures a GPIO to wait a hardware interrupt. Once the GPIO value change from 0 value to 1 value (rising), program gives you a message.

Compile example program

Download an Install IGEP SDK if you don't have it.

First of all you need to initialize a suitable environment in the bash shell console inside your machine.
You can do this sourcing once the environment-setup script.

jdoe@ubuntu ~ $ source /opt/poky/1.2/environment-setup-armv7a-vfp-neon-poky-linux-gnueabi 

• Download source code
• Extract source code
• Build source code:

Cross toolchain tools are available into the built-in virtual machine Poky SDK. You only need open bash terminal prompt and write command:

jdoe@ubuntu ~/Desktop $ arm-poky-linux-gnueabi-gcc -o gpio_example gpio_examplebeta1.c

• Copy binary file to IGEP Board

Execute program

Open a remote terminal and locate your program binary, execute program and pass like a parameter 157 value (GPIO 157):

root@igep00x0:~# ./gpio_example 157 

Result will be:

root@igep00x0:~# ./gpio_example 157
gpio/direction: No such file or directory

poll() GPIO 157 interrupt occurred
............. 

Generate interrupts

Open a second remote terminal and type:

cd /sys/class/gpio/
echo 156 > export 
cd gpio156/ 
echo out > direction
echo 0 > value
echo 1 > value

Result

At first remote terminal you should read a message similar like this:

poll() GPIO 157 interrupt occurred 

How to chek an GPIO

The gpio-int-test.c program shows one way of using the sysfs file /sys/class/gpio/gpioXX/value to block program execution using poll() until the input level on GPIOXX changes.

File:GPIO TEST.tar