tyz1030 / jetsongpio

A C++ library that enables the use of Jetson's GPIOs

JetsonGPIO(C++)

JetsonGPIO(C++) is an C++ port of the NVIDIA's Jetson.GPIO Python library(https://github.com/NVIDIA/jetson-gpio).

Jetson TX1, TX2, AGX Xavier, and Nano development boards contain a 40 pin GPIO header, similar to the 40 pin header in the Raspberry Pi. These GPIOs can be controlled for digital input and output using this library. The library provides almost same APIs as the Jetson.GPIO Python library.

NOTE: The gpio_event module of the Jetson.GPIO Python library is not supported yet.

Installation

Clone this repository, build it, and install it.

git clone https://github.com/pjueon/JetsonGPIO
cd JetsonGPIO/build
make all
sudo make install

Setting User Permissions

In order to use the Jetson GPIO Library, the correct user permissions/groups must
be set first. Or you have to run your program with root permission.

Create a new gpio user group. Then add your user to the newly created group.

sudo groupadd -f -r gpio
sudo usermod -a -G gpio your_user_name

Install custom udev rules by copying the 99-gpio.rules file into the rules.d
directory. The 99-gpio.rules file was copied from NVIDIA's official repository.

sudo cp JetsonGPIO/99-gpio.rules /etc/udev/rules.d/

For the new rule to take place, you either need to reboot or reload the udev rules by running:

sudo udevadm control --reload-rules && sudo udevadm trigger

Library API

The library provides almost same APIs as the the NVIDIA's Jetson GPIO Python library. The following discusses the use of each API:

1. Include the libary

To include the JetsonGPIO use:

#include <JetsonGPIO>

All public APIs are declared in namespace "GPIO". If you want to make your code shorter, you can use:

using namespace GPIO; // optional

To compile your program use:

g++ -o your_program_name your_source_code.cpp -lJetsonGPIO

2. Pin numbering

The Jetson GPIO library provides four ways of numbering the I/O pins. The first two correspond to the modes provided by the RPi.GPIO library, i.e BOARD and BCM which refer to the pin number of the 40 pin GPIO header and the Broadcom SoC GPIO numbers respectively. The remaining two modes, CVM and TEGRA_SOC use strings instead of numbers which correspond to signal names on the CVM/CVB connector and the Tegra SoC respectively.

To specify which mode you are using (mandatory), use the following function call:

GPIO::setmode(GPIO::BOARD);
// or
GPIO::setmode(GPIO::BCM);
// or
GPIO::setmode(GPIO::CVM);
// or
GPIO::setmode(GPIO::TEGRA_SOC);

To check which mode has be set, you can call:

GPIO::NumberingModes mode = GPIO::getmode();

This function returns an instance of enum class GPIO::NumberingModes. The mode must be one of GPIO::BOARD(GPIO::NumberingModes::BOARD), GPIO::BCM(GPIO::NumberingModes::BCM), GPIO::CVM(GPIO::NumberingModes::CVM), GPIO::TEGRA_SOC(GPIO::NumberingModes::TEGRA_SOC) or GPIO::NumberingModes::None.

3. Warnings

It is possible that the GPIO you are trying to use is already being used external to the current application. In such a condition, the Jetson GPIO library will warn you if the GPIO being used is configured to anything but the default direction (input). It will also warn you if you try cleaning up before setting up the mode and channels. To disable warnings, call:

GPIO::setwarnings(false);

4. Set up a channel

The GPIO channel must be set up before use as input or output. To configure the channel as input, call:

// (where channel is based on the pin numbering mode discussed above)
GPIO::setup(channel, GPIO::IN); // channel must be int or std::string

To set up a channel as output, call:

GPIO::setup(channel, GPIO::OUT);

It is also possible to specify an initial value for the output channel:

GPIO::setup(channel, GPIO::OUT, GPIO::HIGH);

5. Input

To read the value of a channel, use:

int value = GPIO::input(channel);

This will return either GPIO::LOW(== 0) or GPIO::HIGH(== 1).

6. Output

To set the value of a pin configured as output, use:

GPIO::output(channel, state);

where state can be GPIO::LOW(== 0) or GPIO::HIGH(== 1).

7. Clean up

At the end of the program, it is good to clean up the channels so that all pins are set in their default state. To clean up all channels used, call:

GPIO::cleanup();

If you don't want to clean all channels, it is also possible to clean up individual channels:

GPIO::cleanup(chan1); // cleanup only chan1

8. Jetson Board Information and library version

To get information about the Jetson module, use/read:

std::string info = GPIO::JETSON_INFO;

To get the model name of your Jetson device, use/read:

std::string model = GPIO::model;

To get information about the library version, use/read:

std::string version = GPIO::VERSION;

This provides a string with the X.Y.Z version format.

9. Check function of GPIO channels

This feature allows you to check the function of the provided GPIO channel:

GPIO::Directions direction = GPIO::gpio_function(channel);

The function returns either GPIO::IN(GPIO::Directions::IN) or GPIO::OUT(GPIO::Directions::OUT) which are the instances of enum class GPIO::Directions.

10. PWM

See samples/simple_pwm.cpp for details on how to use PWM channels.

The JetsonGPIO library supports PWM only on pins with attached hardware PWM controllers. Unlike the RPi.GPIO library, the JetsonGPIO library does not implement Software emulated PWM. Jetson Nano supports 2 PWM channels, and Jetson AGX Xavier supports 3 PWM channels. Jetson TX1 and TX2 do not support any PWM channels.

The system pinmux must be configured to connect the hardware PWM controlller(s) to the relevant pins. If the pinmux is not configured, PWM signals will not reach the pins! The JetsonGPIO library does not dynamically modify the pinmux configuration to achieve this. Read the L4T documentation for details on how to configure the pinmux.