This is a symbolic link to a directory which has a number of files in it:Īctive_low* direction* edge* power/ uevent* value* We will now see a gpio24 device appear under /sys/class gpio that was not there before: Needing to explicitly export a pin can help prevent errors where one might inadvertently attempt to access the wrong pin.Īs an example, we can export GPIO pin 24 (which corresponds to physical pin number 18 on the GPIO connector of the Raspberry Pi) with this shell command:

Later when we are done, we can unexport the pin. This indicates that we want to use a specific GPIO pin and makes it visible in the sysfs file system hierarchy. To export a pin, we write the pin name/number to the pseudo file /sys/class/gpio/export.

If an input pin, read the pin's level (low or high).

If an output pin, set the level to low or high.

Set the pin direction (input or output).

The basic steps to use a GPIO pin from the sysfs interface are the following: Note that the device names starting with 'gpiochip' are the GPIO controllers and we won't directly use them. We'll look at how to use this interface next. On a Raspberry Pi it might look something like this: If your system has a suitable sysfs driver loaded, you will see the GPIO hardware exposed in the file system under /sys/class/gpio.

If you want to follow along and try these commands on a Raspberry Pi, you should check that you did the setup mentioned in the last blog post, specifically you need to be part of the 'gpio' group so you can run these commands without the need to become the root user. However, it can't be easily be used from the file system like sysfs, so the examples here will use sysfs, which is still going to be supported for some time. The new API addresses a number of issues with the sysfs interface. GPIO devices appear as part of sysfs.īefore we continue, I should mention that this interface is being deprecated in favor of a new GPIO character device API. Sysfs is a pseudo filesystem provided by the Linux kernel that makes information about various kernel subsystems, hardware devices, and device drivers available in user space through virtual files. For simple applications you can use it this way, either interactively or by putting the commands in shell scripts. BackgroundĪs we'll see in future installments of this blog series, there are different ways to access GPIO hardware from programs, but sysfs is a simple one that is supported by the Linux kernel and makes the devices visible in the file system so we can experiment from the command line without needing to write any code. I'll show some examples that will work on the Raspberry Pi platform. We won't need to do any programming as we can do this from shell commands. In this blog post we'll look at basic GPIO control using the sysfs interface provided by the Linux kernel.

Neuro programmer 3 cant export