# SPDX-License-Identifier: CC-BY-SA-4.0 # SPDX-FileCopyrightText: 2017-2023 Bartosz Golaszewski libgpiod ======== libgpiod - C library and tools for interacting with the linux GPIO character device (gpiod stands for GPIO device) Since linux 4.8 the GPIO sysfs interface is deprecated. User space should use the character device instead. Version 2 of libgpiod requires GPIO character device uAPI v2 which was first released in linux 5.10. This library encapsulates the ioctl calls and data structures behind a straightforward API. RATIONALE --------- The new character device interface guarantees all allocated resources are freed after closing the device file descriptor and adds several new features that are not present in the obsolete sysfs interface (like event polling, setting/reading multiple values at once or open-source and open-drain GPIOs). Unfortunately interacting with the linux device file can no longer be done using only standard command-line tools. This is the reason for creating a library encapsulating the cumbersome, ioctl-based kernel-userspace interaction in a set of convenient functions and opaque data structures. Additionally this project contains a set of command-line tools that should allow an easy conversion of user scripts to using the character device. BUILDING -------- This is a pretty standard autotools project. The core C library does not have any external dependencies other than the standard C library with GNU extensions. The command-line tools optionally depend on libedit for the interactive feature. To build the project (including command-line utilities) run: ./autogen.sh --enable-tools=yes --prefix= make make install The autogen script will execute ./configure and pass all the command-line arguments to it. If building from release tarballs, the configure script is already provided and there's no need to invoke autogen.sh. For all configure features, see: ./configure --help. TOOLS ----- There are currently six command-line tools available: * gpiodetect - list all gpiochips present on the system, their names, labels and number of GPIO lines * gpioinfo - list lines, their gpiochip, offset, name, and direction, and if in use then the consumer name and any other configured attributes, such as active state, bias, drive, edge detection and debounce period * gpioget - read values of specified GPIO lines * gpioset - set values of specified GPIO lines, holding the lines until the process is killed or otherwise exits * gpiomon - wait for edge events on GPIO lines, specify which edges to watch for, how many events to process before exiting, or if the events should be reported to the console * gpionotify - wait for changed to the info for GPIO lines, specify which changes to watch for, how many events to process before exiting, or if the events should be reported to the console Examples: (using a Raspberry Pi 4B) # Detect the available gpiochips. $ gpiodetect gpiochip0 [pinctrl-bcm2711] (58 lines) gpiochip1 [raspberrypi-exp-gpio] (8 lines) # Read the info for all the lines on a gpiochip. $ gpioinfo -c 1 gpiochip1 - 8 lines: line 0: "BT_ON" output line 1: "WL_ON" output line 2: "PWR_LED_OFF" output active-low consumer="led1" line 3: "GLOBAL_RESET" output line 4: "VDD_SD_IO_SEL" output consumer="vdd-sd-io" line 5: "CAM_GPIO" output consumer="cam1_regulator" line 6: "SD_PWR_ON" output consumer="sd_vcc_reg" line 7: "SD_OC_N" input # Read the info for particular lines. $ ./gpioinfo PWR_LED_OFF STATUS_LED_G_CLK GLOBAL_RESET gpiochip0 42 "STATUS_LED_G_CLK" output consumer="led0" gpiochip1 2 "PWR_LED_OFF" output active-low consumer="led1" gpiochip1 3 "GLOBAL_RESET" output # Read the value of a single GPIO line by name. $ gpioget RXD1 "RXD1"=active # Read the value of a single GPIO line by chip and offset. $ gpioget -c 0 15 "15"=active # Read the value of a single GPIO line as a numeric value. $ gpioget --numeric RXD1 1 # Read two values at the same time. Set the active state of the lines # to low and without quoted names. $ gpioget --active-low --unquoted GPIO23 GPIO24 GPIO23=active GPIO24=active # Set the value of a line and hold the line until killed. $ gpioset GPIO23=1 # Set values of two lines, then daemonize and hold the lines. $ gpioset --daemonize GPIO23=1 GPIO24=0 # Set the value of a single line, hold it for 20ms, then exit. $ gpioset --hold-period 20ms -t0 GPIO23=1 # Blink an LED on GPIO22 at 1Hz $ gpioset -t500ms GPIO22=1 # Blink an LED on GPIO22 at 1Hz with a 20% duty cycle $ gpioset -t200ms,800ms GPIO22=1 # Set some lines interactively (requires --enable-gpioset-interactive) $ gpioset --interactive --unquoted GPIO23=inactive GPIO24=active gpioset> get GPIO23=inactive GPIO24=active gpioset> toggle gpioset> get GPIO23=active GPIO24=inactive gpioset> set GPIO24=1 gpioset> get GPIO23=active GPIO24=active gpioset> toggle gpioset> get GPIO23=inactive GPIO24=inactive gpioset> toggle GPIO23 gpioset> get GPIO23=active GPIO24=inactive gpioset> exit # Wait for three rising edge events on a single GPIO line, then exit. $ gpiomon --num-events=3 --edges=rising GPIO22 10002.907638045 rising "GPIO22" 10037.132562259 rising "GPIO22" 10047.179790748 rising "GPIO22" # Wait for three edge events on a single GPIO line, with time in local time # and with unquoted line name, then exit. $ gpiomon --num-events=3 --edges=both --localtime --unquoted GPIO22 2022-11-15T10:36:59.109615508 rising GPIO22 2022-11-15T10:36:59.129681898 falling GPIO22 2022-11-15T10:36:59.698971886 rising GPIO22 # Wait for falling edge events with a custom output format. $ gpiomon --format="%e %c %o %l %S" --edges=falling -c gpiochip0 22 2 gpiochip0 22 GPIO22 10946.693481859 2 gpiochip0 22 GPIO22 10947.025347604 2 gpiochip0 22 GPIO22 10947.283716669 2 gpiochip0 22 GPIO22 10947.570109430 ... # Block until an edge event occurs. Don't print anything. $ gpiomon --num-events=1 --quiet GPIO22 # Monitor multiple lines, exit after the first edge event. $ gpiomon --quiet --num-events=1 GPIO5 GPIO6 GPIO12 GPIO17 # Monitor a line for changes to info. $ gpionotify GPIO23 11571.816473718 requested "GPIO23" 11571.816535124 released "GPIO23" 11572.722894029 requested "GPIO23" 11572.722932843 released "GPIO23" 11573.222998598 requested "GPIO23" ... # Monitor a line for requests, reporting UTC time and unquoted line name. $ gpionotify --utc --unquoted GPIO23 2022-11-15T03:05:23.807090687Z requested GPIO23 2022-11-15T03:05:23.807151390Z released GPIO23 2022-11-15T03:05:24.784984280Z requested GPIO23 2022-11-15T03:05:24.785023873Z released GPIO23 ... # Monitor multiple lines, exit after the first is requested. $ gpionotify --quiet --num-events=1 --event=requested GPIO5 GPIO6 GPIO12 GPIO17 # Block until a line is released. $ gpionotify --quiet --num-events=1 --event=released GPIO6 BINDINGS -------- High-level, object-oriented bindings for C++, python3 and Rust are provided. They can be enabled by passing --enable-bindings-cxx, --enable-bindings-python and --enable-bindings-rust arguments respectively to configure. C++ bindings require C++11 support and autoconf-archive collection if building from git. Python bindings require python3 support and libpython development files. Please refer to bindings/python/README.md for more information. Rust bindings require cargo support. When building the Rust bindings along the C library using make, they will be automatically configured to build against the build results of the C library. Please refer to bindings/rust/libgpiod/README.md for more information. TESTING ------- A comprehensive testing framework is included with the library and can be used to test both the core library code as well as the kernel-to-user-space interface. The minimum kernel version required to run the tests can be checked in the tests/gpiod-test.c source file (it's subject to change if new features are added to the kernel). The tests work together with the gpio-sim kernel module which must either be built-in or available for loading using kmod. A helper library - libgpiosim - is included to enable straightforward interaction with the module. To build the testing executable add the '--enable-tests' option when running the configure script. If enabled, the tests will be installed next to gpio-tools. As opposed to standard autotools projects, libgpiod doesn't execute any tests when invoking 'make check'. Instead the user must run them manually with superuser privileges. The testing framework uses the GLib unit testing library so development package for GLib must be installed. The gpio-tools programs can be tested separately using the gpio-tools-test.bash script. It requires shunit2[1] to run and assumes that the tested executables are in the same directory as the script. C++, Rust and Python bindings also include their own test-suites. All three reuse the libgpiosim library to avoid code duplication when interacting with gpio-sim. Python test-suite uses the standard unittest package. C++ tests use an external testing framework - Catch2 - which must be installed in the system. Rust bindings use the standard tests module layout and the #[test] attribute. DOCUMENTATION ------------- All API symbols exposed by the core C API and C++ bindings are documented with doxygen markup blocks. Doxygen documentation can be generated by executing 'make doc' given that the doxygen executable is available in the system. Python bindings contain help strings that can be accessed with the help builtin. Rust bindings use rustdoc. Man pages for command-line programs are generated automatically if gpio-tools were selected and help2man is available in the system. CONTRIBUTING ------------ Contributions are welcome - please send questions, patches and bug reports to the linux-gpio mailing list[2] by e-mailing to linux-gpio@vger.kernel.org (add the [libgpiod] prefix to the e-mail subject line). Note that the mailing list quietly drops HTML formatted e-mail, so be sure to send plain text[3]. Code submissions should stick to the linux kernel coding style[4] and follow the kernel patch submission process[5] as applied to the libgpiod source tree. The mailing list archive[6] contains all the historical mails to the list, and is the place to check to ensure your e-mail has been received. Search for "libgpiod" to filter the list down to relevant messages. Those also provide examples of the expected formatting. Allow some time for your e-mail to propagate to the list before retrying, particularly if there are no e-mails in the list more recent than yours. There is a libgpiod github page[7] available for reporting bugs and general discussions and although PRs can be submitted and discussed, upstreambound patches need to go through the mailing list nevertheless while release tarballs should be fetched from kernel.org[8]. For more information, refer to CONTRIBUTING.md in this repository. [1] https://github.com/kward/shunit2 [2] http://vger.kernel.org/vger-lists.html#linux-gpio [3] https://docs.kernel.org/process/email-clients.html [4] https://docs.kernel.org/process/coding-style.html [5] https://docs.kernel.org/process/submitting-patches.html [6] https://lore.kernel.org/linux-gpio/ [7] https://github.com/brgl/libgpiod [8] https://mirrors.edge.kernel.org/pub/software/libs/libgpiod/