4.5 Motion Sensor Implementation

In the previous section we analyzed the functionality of the Arduino example. Also, in the MotionSensor Ports section we constructed the ports of the component.

A Quick Look Inside the Component

The result of this created a new template block of code in the implementation code of the component:

// ----------------------------------------------------------------------
// Handler implementations for user-defined typed input ports
// ----------------------------------------------------------------------

void MotionSensor ::
    run_handler(
        NATIVE_INT_TYPE portNum,
        NATIVE_UINT_TYPE context
    )
{
    // TODO
}

This block of code corresponds to the run port, which means that it will execute every time it gets called.

But what about the output, where is it?

The output port does indeed exist in the project! It exists in the build-fprime-automatic-rpipico/Components/MotionSensor/MotionSensorComponentAc.cpp file.

Do not write code inside *Ac.* files because it is auto-generated code from CMake tool. Any code will be overwritten on the next build. Just inspect!

// ----------------------------------------------------------------------
// Invocation functions for typed output ports
// ----------------------------------------------------------------------

void MotionSensorComponentBase ::
    MpuDataOut_out(
        NATIVE_INT_TYPE portNum,
        const Components::Vector& acceleration
    )
{
    FW_ASSERT(
        portNum < this->getNum_MpuDataOut_OutputPorts(),
        static_cast<FwAssertArgType>(portNum)
    );
    this->m_MpuDataOut_OutputPort[portNum].invoke(
        acceleration
    );
}

This function is ready-to-use in the component's class.

I2C Communication using Arduino Library

In order to develop fprime components while using the Arduino Fw libraries, we need to expose the libraries.

Make sure that library_locations: ./fprime-arduino is in your settings.ini file.

Firstly, we need to include in the CMake the FastIMU library. This can be done by adding the target_use_arduino_libraries("FastIMU") line. The CMakeLists.txt should look like this:

set(SOURCE_FILES
  "${CMAKE_CURRENT_LIST_DIR}/MotionSensor.fpp"
  "${CMAKE_CURRENT_LIST_DIR}/MotionSensor.cpp"
)

target_use_arduino_libraries("FastIMU")

register_fprime_module()

Build to make sure it is included correctly.

The FastIMU library can now be seen by the build system. In the header file, include the library and define the I2C port:

#include "Components/MotionSensor/MotionSensorComponentAc.hpp"
#include "FastIMU.h"
#include <Wire.h>

#define IMU_ADDRESS 0x68

Next, add the essential variables, as used previously in the Arduino example:

// Below `run_handler`
calData calib = { 0 };
AccelData a;
Components::Vector acc_data;
MPU6050* myMPU6050 = new MPU6050();

Setup and Loop Functions

Now, we need to make the corresponding setup() and loop() functions. In the setup function, we need to perform every initialization needed to establish the I2C connection with our board.

void setup() {
  Wire.begin();
  Wire.setClock(400000); // 400kHz clock
  Serial.begin(115200);
  while (!Serial) {
    ;
  }

  int err = IMU.init(calib, IMU_ADDRESS);
  if (err != 0) {
    Serial.print("Error initializing IMU: ");
    Serial.println(err);
    while (true) {
      ;
    }
  }
}

But how will we know the status of the satellite, when it is flying? We can't debug it through USB to get its status.

That's why we need to use telemetry and events!

Next: Defining telemetry and events