The gpio interface

gpio allows access to a specific GPIO pin. The interface is restricted because it provides privileged access to GPIO hardware.

Use snap interface gpio to see which gpio devices are available on the system:

$ snap interface gpio
name:    gpio
summary: allows access to a specific GPIO pin
slots:
  - pi:bcm-gpio-0
  - pi:bcm-gpio-1
  - pi:bcm-gpio-10
[...]

Example

The pi-fancontrol snap provides simple fan control on a Raspberry Pi with a fan connected to GPIO 14 (pin 8). With the snap installed, the following command will connect the interface to the pin:

snap connect pi-fancontrol:gpio pi:bcm-gpio-14

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Developer details

Auto-connect: no
Attributes:

• number (slot): GPIO pin number to export and expose to consuming snaps

Hardware IO interfaces covers some general considerations common to these kinds of devices.

To use a gpio device, the snap developer must add plugs: [ gpio ] to a snap’s snapcraft.yaml. The snap user can then access a specific gpio device with an interface connection.

Unless the snap is expected to actually use a set of gpio pins that is not predefined, it is recommended to define distinct plugs for each used gpio pin, like:

plugs:
  activity-led:
    interface: gpio
  warning-led:
    interface: gpio

This has the advantage of being self-documenting and 1-1 connections like these are easier to track and setup with auto-connections, if the latter is needed.

When the interface is connected, "echo (pin number) > /sys/class/gpio/export" is run internally to enable access to the GPIO pin.

Once connected, the consuming snap can use the device via /sys/class/gpio/gpioN where N is the pin number specified by the connected slot.

Finally, when the interface is disconnected, "echo (pin number) > /sys/class/gpio/unexport" is run internally to disable access to the GPIO pin.

Code examples

The hook and control scripts for pi-fancontrol can be found in the project’s GitHub repository: https://github.com/ogra1/pi-fancontrol-snap

The source code for the GPIO interface is in the snapd repository: https://github.com/snapcore/snapd/blob/master/interfaces/builtin/gpio.go.

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Last updated 9 months ago.