SocketCAN DUNE implementation

CANbus support was not present in DUNE, and therefore had to be added. Since the Raspberry Pi on the Otter is using Linux, we can use the SocketCAN package, which comes with the Linux kernel by default.

Many DUNE tasks use an interface defined by IO::Handle, and so does this CAN implementation. This means that there will be little difference between using CAN or Serial in DUNE. The biggest difference is that CAN uses addresses, and so must have functions to set and get these. The Poll::poll functionality also works, and makes it possible to read with timeout from the CAN bus. Reading it without checking will result in the task waiting until a CAN message is received.

if (Poll::poll(*m_can, 0.01)) {
 m_can->readString(m_can_bfr, sizeof(m_can_bfr));  // Read from CAN bus
 id = m_can->getRXID();  // Address of the most previously read message. Must be called after a read to yield desired data.
}

Here, m_can_bfr is a char array that is used to store the data read from CAN.

m_can_bfr[0] = 0x4f;
m_can_bfr[1] = 0x74;
m_can_bfr[2] = 0x74;
m_can_bfr[3] = 0x65;
m_can_bfr[4] = 0x72;

m_can->setTXID(0x0000feab); // If all messages is sent with the same ID, this only needs to be called once
m_can->write(m_can_bfr, 5); // Write 5 chars to CAN with the previously set ID

Here, m_can_bfr still is a char array.

The CAN implementation uses DUNE/System/Error.hpp to send errors when something goes wrong while initializing SocketCAN. Here is an example on how to initialize SocketCAN while catching eventual errors:

try {
 m_can = new Hardware::SocketCAN(m_args.can_dev, SocketCAN::CAN_BASIC_EFF);
}
 catch(std::runtime_error& e) {
 cri(DTR("Could not open CAN: %s"), e.what());
}

• Linux kernel documentation on CAN