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Knowledge base » Software reference » CAN in – CAN input mailbox

CAN in – CAN input mailbox

By  Stéphane Lovejoy Updated on SD016

Table of Contents

The CAN input mailbox block allows receiving CAN messages with up to 8 bytes long payloads.

It reads frames from the CAN bus and if the frame address matches the mailbox address, the data is applied to the output port of the block. The CAN input mailbox block features a second output that indicates that new data has been received. The value on the output data port will remain unchanged until new data are received.

Simulink block

Signal specification

  • The data output signal returns a vector containing the data read from the CAN bus. The vector length can be configured with the  Number of signals parameter. The output data type is configured by the Signal type parameter.
  • The second signal is the data valid output. It is set to 1 each time new data are available.

Parameters

  • CAN address: sets the CAN input mailbox address. If a CAN frame with a matching address is received the frame data is applied to the data output port of the block.
  • Signal Type: defines the type of the data output (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 read. (little-endian or big-endian)
  • Initial value: sets the initial data value of the data output before any data are received. The value is interpreted as a uint64.
  • 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 output signal returns a vector containing the data read from the CAN bus. The vector length can be configured with the  Number of signals parameter. The output data type is configured by the Signal type parameter.
  • The second signal is the data valid output. It is set to 1 each time new data are available.

Parameters

  • CAN address: sets the CAN input mailbox address. If a CAN frame with a matching address is received the frame data is applied to the data output port of the block.
  • Signal Type: defines the type of to the data output (int8, uint8, int16, uint16, int32, uint32, in64, uint64, float, or double).
  • Number of signals:sets the vector length of the data output.
  • Byte order: defines the byte order in which the data will be read. (little-endian or big-endian)
  • Initial value: sets the initial data value of the data output before any data is received. The value is interpreted as a uint64.
  • Baud rate: configures the baud rate of the CAN bus. Baud rates up to 1 Mbit/s are supported.

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_ConfigureInputMailbox(unsigned int mailboxId, unsigned int canAddress, unsigned int dataLength, tEndianness endianness = LITTLE_ENDIAN);Code language: C++ (cpp)

Configures a CAN input 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: sets the CAN input mailbox address. If a CAN frame with a matching address is received the frame data is stored in the mailbox and can be read using the Can_Read() function. The CAN address range is 0 to 2047 (11 bits).
  • dataLength: number of bytes of data to read from the CAN bus (1 to 8 bytes).
  • endianness: defines the bytes order (BIG_ENDIAN or LITTLE_ENDIAN).

Return value

  • bool: returns false if too many output mailboxes were created or if canAddress is out of range.
void Can_ConfigureInputMailboxInitialValue(unsigned int mailboxId, uint64_t data);Code language: C++ (cpp)

Configures the initial value returned by the Can_Read() function before any CAN frame is received in the 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.
  • data: default data which will be returned by any call of Can_Read() before data is received on the CAN input mailbox.
// 64-bit (8 bytes) types: uint64, int64 and double
int Can_Read(unsigned int maildboxId, uint64_t& data); //8 bytes
int Can_Read(unsigned int maildboxId, int64_t& data); //8 bytes
int Can_Read(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_Read(unsigned int maildboxId, unsigned int& dataLow, unsigned int& dataHigh); //8 bytes
int Can_Read(unsigned int maildboxId, unsigned int& dataLow); //4 bytes
int Can_Read(unsigned int maildboxId, int& dataLow, int& dataHigh); //8 bytes
int Can_Read(unsigned int maildboxId, int& dataLow); //4 bytes
int Can_Read(unsigned int maildboxId, float& dataLow, float& dataHigh); //8 bytes
int Can_Read(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_Read(unsigned int maildboxId, uint16_t& dataLow, uint16_t& dataMedLow, uint16_t& dataMedHigh, uint16_t& dataHigh); //8 bytes
int Can_Read(unsigned int maildboxId, uint16_t& dataLow, uint16_t& dataMedLow, uint16_t& dataMedHigh); //6 bytes
int Can_Read(unsigned int maildboxId, uint16_t& dataLow, uint16_t& dataMedLow); //4 bytes
int Can_Read(unsigned int maildboxId, uint16_t& dataLow); //2 bytes
int Can_Read(unsigned int maildboxId, int16_t& dataLow, int16_t& dataMedLow, int16_t& dataMedHigh, int16_t& dataHigh); //8 bytes
int Can_Read(unsigned int maildboxId, int16_t& dataLow, int16_t& dataMedLow, int16_t& dataMedHigh); //6 bytes
int Can_Read(unsigned int maildboxId, int16_t& dataLow, int16_t& dataMedLow); //4 bytes
int Can_Read(unsigned int maildboxId, int16_t& dataLow); //2 bytesCode language: C++ (cpp)
// array of uint8
typedef struct {
  uint8_t data[8];
} tCanMsg;
 
int Can_Read(unsigned int maildboxId, tCanMsg& canMsg); //1 to 8 bytesCode language: C++ (cpp)

These functions are used to read data received in the input mailbox. The data read will remain unchanged until new data are received.

They have to be called during the control interrupt.

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.
  • data: data read from the input mailbox. 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_ConfigureInputMailbox() defines it.

Return value

  • int: returns 1 if new data is available since the last read. 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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