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Knowledge base » Software reference » CAN out – CAN output mailbox

CAN out – CAN output mailbox

By  Stéphane Lovejoy Updated on SD017

Table of Contents

The CAN output mailbox block allows sending CAN messages with up to 8 bytes long payloads.

It supports two operating modes:

  • On-demand mode: the user manually triggers the message transmissions.
  • Periodical mode: the message is sent periodically, whether the data has been changed or not. The user can configure the transmission frequency.

Simulink block

Signal specification

  • The data input signal supports a vector of data. The accepted data type is configured by Signal type parameter. The vector length can be configured with Number of signals parameter.
  • The second input is the send data signal. It is used to initiate a data transmission when the on-demand mode has been selected. Data is sent upon a rising edge on this signal.

Parameters

  • CAN address : sets the CAN output mailbox address. It also sets the CAN unique identifier of the data frame.
  • Signal Type : defines the data type accepted in the data input (int8, uint8, int16, uint16, int32, uint32, in64, uint64, float, or double).
  • Number of signals : sets the vector length of the data output. (from 1 to 8)
  • Byte order : defines the byte order in which the data will be sent. Either little-endian or big-endian.
  • Tx frequency : Sets the data transmission frequency if the periodical mode has been selected.
  • Baud rate : configures the baud rate of the CAN bus. Baud rates up to 1 Mbit/s are supported.

PLECS block

Signal specification

  • The data input signal supports a vector of data. The accepted data type is configured by Signal type parameter. The vector length can be configured with Number of signals parameter.
  • The second input is the send data signal. It is used to initiate a data transmission when the on-demand mode has been selected. Data is sent upon a rising edge on this signal.

Parameters

  • CAN address: sets the CAN output mailbox address. It also sets the CAN unique identifier of the data frame.
  • Signal Type: defines the data type accepted in the data input (int8, uint8, int16, uint16, int32, uint32, in64, uint64, float, or double).
  • Number of signals: sets the vector length of the data output. (from 1 to 8)
  • Byte order: defines the byte order in which the data will be sent. Either little-endian or big-endian.
  • Tx frequency: sets the data transmission frequency if the periodical mode has been selected.

C++ functions

void Can_ConfigureCanBus(unsigned int baudrate);Code language: C++ (cpp)

Configures the baud rate of the CAN bus. Baud rates up to 1 Mbit/s are supported.

It has to be called in UserInit().

Parameters

  • baudrate: Baud rate of the CAN bus in bit/s (up to 1’000’000 bit/s)
bool Can_ConfigureOutputMailbox(unsigned int maildboxId, unsigned int canAddress, unsigned int dataLength, float maxTxFrequency = 100, tEndianness endianness = LITTLE_ENDIAN);Code language: C++ (cpp)

Configures a CAN output mailbox.

It has to be called in UserInit().

Parameters

  • mailboxId: a unique ID used to distinguish mailboxes from each other. This ID must be unique throughout the code for all ETH and CAN input/output mailboxes.
  • canAddress: address to whom data will be sent. This parameter is also used as the CAN identifier. Therefore, it also represents the message priority. CAN address range is 0 to 2047 (11 bits).
  • dataLength: number of bytes of data to transmit (1 to 8 bytes).
  • maxTxFrequency: maximal frequency at which data can be sent. The frequency must be a multiple of the interrupt frequency. If the requested frequency is not achievable, it will be automatically set to the closest valid frequency.
  • endianness: defines the frame bytes order. (BIG_ENDIAN or LITTLE_ENDIAN)

Return value

  • bool: returns false if the configuration fails. The reason may be that too many output mailboxes were created or if canAddress is out of range.
// 64-bit (8 bytes) types: uint64, int64 and double
int Can_Write(unsigned int maildboxId, uint64_t data); //8 bytes
int Can_Write(unsigned int maildboxId, int64_t data); //8 bytes
int Can_Write(unsigned int maildboxId, double data); //8 bytesCode language: C++ (cpp)
// 32-bit (4 bytes) types: int32, uint32 and float
// dataLow  represents the bytes 0, 1, 2 and 3
// dataHigh represents the bytes 4, 5, 6 and 7
int Can_Write(unsigned int maildboxId, unsigned int dataLow, unsigned int dataHigh); //8 bytes
int Can_Write(unsigned int maildboxId, unsigned int dataLow); //4 bytes
int Can_Write(unsigned int maildboxId, int dataLow, int dataHigh); //8 bytes
int Can_Write(unsigned int maildboxId, int dataLow); //4 bytes
int Can_Write(unsigned int maildboxId, float dataLow, float dataHigh); //8 bytes
int Can_Write(unsigned int maildboxId, float dataLow); //4 bytesCode language: C++ (cpp)
// 16-bit (2 bytes) types: int16 and uint16
// dataLow     represents the bytes 0 and 1
// dataMedLow  represents the bytes 2 and 3
// dataMedHigh represents the bytes 4 and 5
// dataHigh    represents the bytes 6 and 7
int Can_Write(unsigned int maildboxId, uint16_t dataLow, uint16_t dataMedLow, uint16_t dataMedHigh, uint16_t dataHigh); //8 bytes
int Can_Write(unsigned int maildboxId, uint16_t dataLow, uint16_t dataMedLow, uint16_t dataMedHigh); //6 bytes
int Can_Write(unsigned int maildboxId, uint16_t dataLow, uint16_t dataMedLow); //4 bytes
int Can_Write(unsigned int maildboxId, uint16_t dataLow); //2 bytes
int Can_Write(unsigned int maildboxId, int16_t dataLow, int16_t dataMedLow, int16_t dataMedHigh, int16_t dataHigh); //8 bytes
int Can_Write(unsigned int maildboxId, int16_t dataLow, int16_t dataMedLow, int16_t dataMedHigh); //6 bytes
int Can_Write(unsigned int maildboxId, int16_t dataLow, int16_t dataMedLow); //4 bytes
int Can_Write(unsigned int maildboxId, int16_t dataLow); //2 bytesCode language: C++ (cpp)
// array of uint8
typedef struct {
  uint8_t data[8];
} tCanMsg;

int Can_Write(unsigned int maildboxId, tCanMsg& data); //1 to 8 bytesCode language: C++ (cpp)

These functions are used to send data on the CAN bus.

They have to be called during the control interrupt.

Parameters

  • maildboxId: a unique ID used to distinguish mailboxes from each other. This ID must be unique throughout the code for all ETH and CAN input/output mailboxes.
  • data: data which will be sent. Several data types and prototypes are available. Note that the prototype used will not affect the length of the data sent, only the dataLength in Can_ConfigureOutputMailbox() defines it.

Return value

  • int: returns 1 if the data has successfully been loaded in the write buffer. Returns 0 otherwise.

Stéphane is a senior software development engineer at imperix. He authored and co-authored numerous software reference articles and documentation, notably related to Cockpit.

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