I2C

Installation

mkdir build
cd build
cmake ..
make
sudo make install

Integration

CMake

To use I2C in an executable MyProgram, your CMakeLists.txt would look like this:

find_package(ottojo.I2C REQUIRED)

add_executable(MyProgram main.cpp)
target_link_libraries(MyProgram PRIVATE ottojo.I2C::I2C)

Usage

The first step is always to instantiate the I2C Bus:

auto bus = std::make_shared<i2c::Bus>("/dev/i2c-1");

Before you can communicate with a target device, the Bus needs to be locked:

constexpr auto DEVICE_ADDRESS = 0x40;
bus.lock(DEVICE_ADDRESS).write<3>({std::byte{0xA}, std::byte{0xB}, std::byte{0xC}});

While the Bus is locked, no other thread can access the Bus. If you need to write to the device, and then read from the device without another thread interfering, you can hold on to the lock as long as needed.

std::array<std::byte, 7> dataFromDevice{};
{
    auto lockedBus = bus.lock(DEVICE_ADDRESS);
    lockedBus.write<3>({byte{0xA}, byte{0xB}, byte{0xC}});
    dataFromDevice = lockedBus.read<7>();
}

A common use case is first writing a register address, and then reading multiple bytes starting at that address. The readFrom function does just that:

constexpr auto REGISTER_ACCELERATION = std::byte{0x7};
auto acceleration = bus.lock(DEVICE_ADDRESS).readFrom<4>(REGISTER_ACCELERATION);

Chip Driver

PCA9685

The library provides a driver for the PCA9685 PWM controller:

auto pwmController = i2c::PCA9685(std::make_shared<i2c::Bus>("/dev/i2c-0"));
pwmController.setAllOff();
pwmController.setOnTime(0, 0);
pwmController.setOffTime(0, 512);

The On/Off time has to be determined manually currently, see the datasheet for information on the integrated counter and prescaler.

Board Driver

Servo Hat

The library provides a driver for the "SparkFun Servo pHAT", based on the PCA9685 PWM controller.

auto servoHat = i2c::ServoHat(std::make_shared<i2c::Bus>("/dev/i2c-0"));
servoHat.setServo(0, 1500);

This sets the servo 0 to 1500µS, which corresponds to the midpoint on most servos.