CAN Bus

NeuralPlex utilizes the Qt QCanBus class for all CAN bus messaging. The reference application provides CanBus.cpp and CanBus.hpp wrapper class that handles sending, receiving, timeout, and other related events.

The module is built upon the foundational principles of Linux Socket CAN, offering a simplified interface through functions and signals to streamline day-to-day tasks. At its core, the module employs socket programming to transmit and receive CAN messages. NeuralPlex supports concurrent operations on four CAN buses, namely CAN0, CAN1, CAN3, and CAN4.

Additionally, it extends its functionality to support virtual CAN interfaces, vcan0, catering to desktop environment testing requirements.

To utilize the NeuralPlex CanBus class, create a new class and use a QSharedPointer to pass in the pointer to the CanBus class. For example, create a new Vehicle class and add the following:

Vehicle Class

Vehicle.cpp

// This class establishes a connection to a CAN bus & is used
// to send/receive CAN frames.
// To watch for CAN frames, connect to the frameArrived signal.
// To send CAN frames, connect a signal to the writeFrame() slot.
Vehicle::Vehicle(QSharedPointer<CanBus> canBus, QObject *parent)
    : QObject(parent)
    , m_canBus(canBus)
{
    // Set the CAN IDs that the Vehicle class needs to monitor
    m_canBus->setVehicleIds({ DD1, CCVS1, SENSOR });

    // Get notified when a CAN message for the Vehicle class arrives
    connect(m_canBus.data(), &CanBus::vehicleFrameArrived,
      this, &Vehicle::processMessage);

    // Start a 100ms timer to send CAN messages
    startTimer(100);
}

Receving CAN messages

Vehicle.cpp

// Process CAN messages by decoding the signal and reporting to QML
void Vehicle::processMessage(const QCanBusFrame &frame)
{
    const auto frameId = frame.frameId();
    const auto *payload = (uint8_t*)(frame.payload().constData());

    // Begin the switch statement for processing each CAN frame
    switch (frameId)
    {
    case DD1: {
        setFuelLevel(decode(payload, 8, 8, false, false, 0.4, 0));
        break;
    }
    case CCVS1: {
        setSpeedometer(decode(payload, 8, 16, false, false, 0.00390625, 0));
        break;
    }
    case SENSOR: {
        setSensor1(decode(payload, 0, 8, false, true, 0.4, 0));
        setSensor2(decode(payload, 8, 8, false, true, 0.4, 0));
        setSensor3(decode(payload, 16, 8, false, true, 0.4, 0));
        setSensor4(decode(payload, 24, 8, false, true, 0.4, 0));
        break;
    }
    default:
        break;
    }
}

Sending CAN messages

Vehicle.cpp

void Vehicle::startTimer(uint8_t val)
{
    // Setup QTimer instance to expire as defined by timeout value
    QTimer *can = new QTimer(this);
    connect(can, SIGNAL(timeout()), this, SLOT(sendCAN()));
    can->start(val);
}

void Vehicle::sendCAN()
{
    QCanBusFrame frame;
    uint8_t dd1Payload[8] {0};
    frame.setFrameId(DD1);
    encode(dd1Payload, fuelLevel(), 8, 8, false, false, 0.4, 0);
    frame.setPayload(QByteArray::fromRawData((const char*)dd1Payload, 8));
    m_canBus->writeFrame(frame);

    uint8_t ccvs1Payload[8] {0};
    frame.setFrameId(CCVS1);
    encode(ccvs1Payload, speedometer(), 8, 16, false, false, 0.00390625, 0);
    frame.setPayload(QByteArray::fromRawData((const char*)ccvs1Payload, 8));
    m_canBus->writeFrame(frame);

    uint8_t sensorPayload[8] {0};
    frame.setFrameId(SENSOR);
    encode(sensorPayload, sensor1(), 0, 8, false, true, 0.4, 0);
    encode(sensorPayload, sensor2(), 8, 8, false, true, 0.4, 0);
    encode(sensorPayload, sensor3(), 16, 8, false, true, 0.4, 0);
    encode(sensorPayload, sensor4(), 24, 8, false, true, 0.4, 0);
    frame.setPayload(QByteArray::fromRawData((const char*)sensorPayload, 8));
    m_canBus->writeFrame(frame);
}

CanBus Setup

main.cpp

// Create instance of CanBus class and share the pointer
// with other classes so they are notified when messages arrive
QSharedPointer<CanBus> canBusPointer = QSharedPointer<CanBus>::create("CAN0");
Vehicle* vehicle = new Vehicle(canBusPointer);

// Setup the context properties so the front end (QML) can access the back end (C++)
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("vehicle", vehicle);