SocketCAN Device Drivers

  • include/nuttx/net/netdev.h. All structures and APIs needed to work with drivers are provided in this header file. The structure struct net_driver_s defines the interface and is passed to the network via netdev_register().

  • include/nuttx/can.h. CAN & CAN FD frame data structures.

  • int netdev_register(FAR struct net_driver_s *dev, enum net_lltype_e lltype)'. Each driver registers itself by calling netdev_register().

  • Include/nuttx/net/can.h. contains lookup tables for CAN dlc to CAN FD len sizes named

    extern const uint8_t g_can_dlc_to_len[16];
extern const uint8_t g_len_to_can_dlc[65];

  • Initialization sequence is as follows.

    1. xxx_netinitialize(void) is called on startup of NuttX in this function you call your own init function to initialize your CAN driver

    2. In your own init function you create the net_driver_s structure set required init values and register the required callbacks for SocketCAN

    3. Then you ensure that the CAN interface is in down mode (usually done by calling the d_ifdown function)

    4. Register the net_driver_s using netdev_register

  • Receive sequence is as follows.

    1. Device generates interrupt

    2. Process this interrupt in your interrupt handler

    3. When a new CAN frame has been received you process this frame

    4. When the CAN frame is a normal CAN frame you allocate the can_frame struct, when it’s a CAN FD frame you allocate a canfd_frame struct (note you can of course preallocate and just use the pointer).

    5. Copy the frame from the driver to the struct you’ve allocated in the previous step.

    6. Point the net_driver_s d_buf pointer to the allocated can_frame

    7. Call the can_input(FAR struct net_driver_s *dev) function include/nuttx/net/can.h

  • Transmit sequence is as follows.

    1. Socket layer executes d_txavail callback

    2. An example of the txavail function can be found in arch/arm/src/s32k1xx/s32k1xx_flexcan.c

    3. An example of the txpoll function can be found in arch/arm/src/s32k1xx/s32k1xx_flexcan.c

    4. In your transmit(struct driver_s *priv) function you check the length of net_driver_s.d_len whether it matches the size of a struct can_frame or struct canfd_frame then you cast the content of the net_driver_s.d_buf pointer to the correct CAN frame struct