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GPIOD Usage

GPIOD Introduction

The GPIO sysfs interface has been deprecated since Linux 4.8. Userspace should instead use libgpiod to interact with GPIO character devices.

Key features​

  • Easy to use: libgpiod provides a simple API that makes controlling and operating GPIO devices easy to understand. Developers only need to understand basic GPIO concepts and function interfaces to use it.
  • Independence: libgpiod is a standalone user-space library that does not depend on any particular hardware platform or chip. It is suitable for a wide range of embedded platforms that support GPIO control, such as the Radxa ROCK series, Raspberry Pi, BeagleBone, and so on.
  • Multiple Programming Languages Support: libgpiod supports C language natively, and also provides Python bindings (python3-libgpiod) and wrappers for other languages, which makes it easy to use in different programming languages.
  • Efficient Event Listening: libgpiod provides functionality for asynchronous event listening, such as waiting for GPIO state changes. This allows developers to implement efficient event-driven applications.
  • GPIO specification support: libgpiod provides support for different GPIO specifications and numbering methods, including GPIO numbering and physical pin numbering.

Command Line Tools​

libgpiod provides a variety of command line tools, for viewing and control GPIO devices.

gpioinfo​

Display GPIO device information:

radxa@radxa-zero2:~$ gpioinfo
gpiochip0 - 85 lines:
        line   0:     "PIN_27"       unused   input  active-high
        line   1:     "PIN_28"       unused   input  active-high
        line   2:      "PIN_7"       unused   input  active-high
        line   3:     "PIN_11"       unused   input  active-high
        line   4:     "PIN_13"       unused   input  active-high
        line   5:     "PIN_15"       unused   input  active-high
        line   6:     "PIN_18"       unused   input  active-high
        line   7:     "PIN_40"       unused   input  active-high
        line   8:      unnamed       unused   input  active-high
        line   9:      unnamed       unused   input  active-high
...

gpiodetect​

List all GPIO controllers in the system:

radxa@rock-pi-s:~$ gpiodetect
gpiochip0 [gpio0] (32 lines)
gpiochip1 [gpio1] (32 lines)
gpiochip2 [gpio2] (32 lines)
gpiochip3 [gpio3] (32 lines)
gpiochip4 [gpio4] (32 lines)

gpioget​

Read GPIO input:

radxa@radxa-zero2:~$ gpioget gpiochip0 0
1

gpioset​

info

Unlike the traditional sysfs, by default gpioset will exit as soon as the GPIO output has been set. Whether the output will stay at the same level is platform-defined, so you cannot rely on this behavior.

To persistently set the GPIO level, please follow the below example to set the working mode to signal.

Set GPIO output:

radxa@radxa-zero2:~$ gpioset -m signal gpiochip0 0=1
(Press Ctrl+C to stop)

gpiomon​

Monitor GPIO events:

radxa@radxa-zero2:~$ gpiomon gpiochip0 0
(GPIO event output)

gpiofind​

Find GPIO chip and line:

radxa@radxa-zero2:~$ gpiofind PIN_27
gpiochip0 0
tip

You can combine gpiofind and gpioget/gpioset/gpiomon to avoid hard-coding GPIO line info in your script:

radxa@radxa-zero2:~$ gpioget $(gpiofind PIN_27)
1

Programming Reference​

The relevant header files need to be installed before use:

sudo apt-get update
sudo apt-get install libgpiod-dev

Convert vendor gpio to libgpiod​

  • Naming conventions

There are usually 5 groups (also called banks) of GPIOs on the Rockchip platform: GPIO0~GPIO4 (varies from chip to chip), each group has 32 GPIOs. Each group of GPIOs is divided into 4 groups, A/B/C/D, with 8 GPIOs in each group (0~7, also called bank_idx). rockchip.h)). So the GPIOs can be named from GPIO0_A0 to GPIO4_D7. Taking GPIO3_C5 as an example, we can deduce that its bank is 3 and its bank_idx is 21, i.e. GPIO3_C5 is the 21st GPIO in group 3.

  • Correspondence to libgpiod

The GPIO bank of Rockchip platform corresponds to gpiochip in libgpiod, and bank_idx corresponds to gpio line. Take GPIO3_C5 as an example, it is in libgpiod, gpiochip is 3 and line is 21.