Sending different datatype data in single CAN message in STM32

Question

While working with the CAN on STM32L4, I am trying to send three different data types of data i.e. float, bool and float value. As in one message 8 byte can be sent, all three data I am sending in single message.

my data looks like

float tf;
uint16_t sl;
bool status_tf;
bool status_sl;

It would be great if I can get some direction, How I can combine all three data type in single CAN message?

Until now, I have tried with sprintf() with print format specifier. and storing combined result in char TxData[8]; But Not getting any fruitful result.

To send the data, standard HAL_CAN_AddTxMessage() used.

HAL_CAN_AddTxMessage(&hcan1, &TxHeader, TxData, &TxMailbox);

Answer 1

How I can combine all three data type in single CAN message?

At first blush, one might consider a struct to hold all the data and then send that.

// First idea, but is it too big?
typedef struct {
  float tf;
  uint16_t sl;
  bool status_tf;
  bool status_sl;
} my_data;

The size of my_data may be more than 8 bytes due to padding and bool may be more than 1 byte.

Consider using memcpy() to cope with alignment issues. A good compiler will emit efferent code for such small copies. I'd assign the bool to charTxData[6] (& 7) to cope with a wide bool. Only the value of 0 or 1 will assign.

unsigned char TxData[8];

memcpy(&charTxData[0], &tf, 4);
memcpy(&charTxData[4], &sl, 2);
charTxData[6] = status_tf;
charTxData[7] = status_sl;

HAL_CAN_AddTxMessage(&hcan1, &TxHeader, TxData, &TxMailbox);

To recover the data, reverse the copying.

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Pedantic code would also check sizes:

_Static_assert(sizeof tf == 4, "Unusual tf size");
_Static_assert(sizeof sl == 2, "Unusual sl size");

If endian-ness of uint16_t and/or float or float encoding may differ, additional code is warranted.