Controlling multiple Myxa over UAVCAN-v0

Support Telega electric propulsion
1

I’m trying to control multiple Myxas over UAVCAN-v0 line from a C language STM32 application.
For debugging I’m checking the traffic over CAN with a Babel board and UAVCAN Tool GUI.

So far I have succeeded in

  • Broadcasting Node Status
  • Replying to GetNodeInfo

The part I’m experiencing problems with is ESC control.
This is the code I call every 100ms to update their value (for the sake of testing I set them all to the same RPM)

    static inline void publishSetEscRPM(int32_t new_rpm)
    {
        static uint8_t transfer_id;

        uint8_t buffer[UAVCAN_ESC_RPM_COMMAND_MESSAGE_SIZE];

        memset(buffer, 0, UAVCAN_ESC_RPM_COMMAND_MESSAGE_SIZE);

        for (uint_fast8_t i = 0; i < M3U_MOTOR_NO; i++)
        {
            canardEncodeScalar(&(buffer[0]), 0 + (18UL * i), 18, &new_rpm);
        }
        const int16_t enqueued_frames = canardBroadcast(&canard,
                                                        0,
                                                        UAVCAN_ESC_RPM_DATA_TYPE_ID,
                                                        &transfer_id,
                                                        CANARD_TRANSFER_PRIORITY_HIGH,
                                                        &(buffer[0]),
                                                        UAVCAN_ESC_RPM_COMMAND_MESSAGE_SIZE);

        (void) enqueued_frames;
    }

As long as I remain within one single CAN telegram, which implies

M3U_MOTOR_NO = 3
UAVCAN_ESC_RPM_COMMAND_MESSAGE_SIZE=7

everything works smoothly.

But if I try with

M3U_MOTOR_NO = 4
UAVCAN_ESC_RPM_COMMAND_MESSAGE_SIZE=9

I cant’ control Myxa anymore and UAVCAN Tool GUI complains about

Transfer Error. CRC mismatch

I’m confused by the fact that the mutli-CAN-frame GetNodeInfo reply goes through flawlessly.

Any suggestions?

Thank you.

2

You are setting the data type signature to zero (second argument to canardBroadcast), hence the CRC is computed incorrectly. If you used the correct signature it would be working properly.

3

It makes perfectly sense.

Thank you.

For anybody who may be interested, signatures for standard namespace uavcan may be found here.