Handling GPIO InterruptPins

Steps to Read and Configure GPIOs with Interrupts

1. Access GPIO Pins via sysfs Interface

In Linux, the sysfs interface allows access to GPIO pins. The following steps will help you list and configure GPIOs.

• List Available GPIOs:

  • In most cases, GPIO pins are mapped under /sys/class/gpio.

  • First, check if the GPIOs are exported by looking at this directory:

    ls /sys/class/gpio/

• Export a GPIO Pin:

  • If a GPIO pin is not visible, export it by writing its number into the export file.

    echo <GPIO_PIN_NUMBER> > /sys/class/gpio/export

  • For example, to export GPIO pin 22:

    echo 22 > /sys/class/gpio/export

• Check GPIO Pin Direction:

  • After exporting the pin, check or configure the GPIO direction (input or output) by interacting with the direction file.

    cat /sys/class/gpio/gpio22/direction

  • To set the GPIO as an input pin (necessary for interrupt):

    echo "in" > /sys/class/gpio/gpio22/direction

2. Enable GPIO Interrupts

Once a GPIO pin is exported, you can configure its edge detection, which enables the interrupt functionality.

• Set the Interrupt Trigger:

  • You can configure which edge (voltage change) the GPIO will respond to by writing to the edge file. Possible values include:

    • none: No interrupt (default).
    • rising: Trigger on rising edge (low to high).
    • falling: Trigger on falling edge (high to low).
    • both: Trigger on both edges (rising and falling).

  • For example, to trigger on both rising and falling edges:

    echo "both" > /sys/class/gpio/gpio22/edge

3. Monitor GPIO Interrupt Events

• A more practical approach for real-time monitoring is to use the poll() system call in a C or Python program. Alternatively, you can use inotifywait in a terminal to monitor changes.

• To use inotifywait:

  sudo apt-get install inotify-tools

  inotifywait -m /sys/class/gpio/gpio22/value

• This will display a notification whenever the value of the GPIO changes, i.e., when an interrupt occurs.