C281x eCAN Receive - Enhanced Control Area Network receive mailbox

Library

Embedded Coder/ Embedded Targets/ Processors/ Texas Instruments C2000/ C281x

Description

Use the C281x enhanced Control Area Network (eCAN) Receive block to receive eCAN messages through an eCAN mailbox. The eCAN module on the DSP chip provides serial communication capability and has 32 mailboxes configurable for receive or transmit. The C281x supports eCAN data frames in standard or extended format.

The C281x eCAN Receive block has up to three output ports.

• f0 outputs a function call when the block receives a new message. Connect a function call subsystem to this port.

• Msg outputs the message data as a vector. The vector is always 8 bytes long. Use Data type to and is composed of elements of the data type.

• len outputs the length of the eCAN message. Select Output message length to create this output.

To use the eCAN Receive block with the eCAN Pack block in the canmsglib, set Data type to CAN_MESSAGE_TYPE.

Dialog Box

Mailbox number

Unique number between 0 and 15 for standard or between 0 and 31 for enhanced CAN mode. It refers to a mailbox area in RAM. In standard mode, the mailbox number determines priority.

Message identifier

Identifier of length 11 bits for standard frame size or length 29 bits for extended frame size in decimal, binary, or hex. If in binary or hex, use bin2dec(' ') or hex2dec(' '), respectively, to convert the entry. The message identifier is associated with a receive mailbox. Only messages that match the mailbox message identifier are accepted into it.

Message type

Select Standard (11-bit identifier) or Extended (29-bit identifier).

Sample time

Frequency with which the mailbox is polled to determine if a new message has been received. A new message causes a function call to be emitted from the mailbox. If you want to update the message output only when a new message arrives, then the block needs to be executed asynchronously. To execute this block asynchronously, set Sample Time to -1, check the Post interrupt when message is received box, and refer to Asynchronous Interrupt Processing for a discussion of block placement and other necessary settings.

Note   For information about setting the timing parameters of the CAN module, see Configuring Timing Parameters for CAN Blocks.

Data type

Select one of the following options:

• uint8 (vector length = 8 elements)

• uint16 (vector length = 4 elements)

• uint32 (vector length = 2 elements)

• CAN_MESSAGE_TYPE (Select this option to use the eCAN receive block with the CAN Unpack block.)

The length of the vector for the received message is at most 8 bytes. If the message is less than 8 bytes, the data buffer bytes are right-aligned in the output. The data are unpacked as follows using the data buffer, which is 8 bytes.

For uint8 data, eCAN Receive reads each unit of 8 bytes in the registers, and outputs 8-bit data to 8 elements (using the lower part of the 16-bit memory):

Output[0] = data_buffer[0];
Output[1] = data_buffer[1];
Output[2] = data_buffer[2];
Output[3] = data_buffer[3];
Output[4] = data_buffer[4];
Output[5] = data_buffer[5];
Output[6] = data_buffer[6];
Output[7] = data_buffer[7];

For uint16 data,

Output[0] = data_buffer[1..0];
Output[1] = data_buffer[3..2];
Output[2] = data_buffer[5..4];
Output[3] = data_buffer[7..6];

For uint32 data,

Output[0] = data_buffer[3..0];
Output[1] = data_buffer[7..4];

For example, if the received message has two bytes:

data_buffer[0] = 0x21
data_buffer[1] = 0x43

The uint16 output would be:

Output[0] = 0x4321
Output[1] = 0x0000
Output[2] = 0x0000
Output[3] = 0x0000

When you select CAN_MESSAGE_TYPE, the block outputs the following struct data (defined in can_message.h):

struct {
  
  /* Is Extended frame */
  uint8_T Extended;

  /* Length */
  uint8_T Length;

  /* RTR */
  uint8_T Remote;

  /* Error */
  uint8_T Error;

  /* CAN ID */
  uint32_T ID;
  
  /* 
  TIMESTAMP_NOT_REQUIRED is a macro that will be defined by Target teams 
  PIL, xPC if they do not require the timestamp field during code
  generation. By default, timestamp is defined. If the targets do not require
  the timestamp field, they should define the macro TIMESTAMP_NOT_REQUIRED before
  including this header file for code generation.
  */
  #ifndef TIMESTAMP_NOT_REQUIRED
      /* Timestamp */
      double Timestamp;
  #endif

  /* Data field */
  uint8_T Data[8];

};

Output message length

Select to output the message length in bytes to the third output port. If not selected, the block has only two output ports.

Post interrupt when message is received

Select this check box to post an asynchronous interrupt when a message is received.

Interrupt line

Select the interrupt line the asynchronous interrupt uses. This action sets bit 2 (GIL) in the Global Interrupt Mask Register (CANGIM):

• 1 maps the global interrupts to the ECAN1INT line.

• 0 maps the global interrupts to the ECAN0INT line.

References

For detailed information on the eCAN module, see TMS320F28x DSP Enhanced Control Area Network (eCAN) Reference Guide, Literature Number SPRU074A, available at the Texas Instruments Web site.

See Also

C281x eCAN Transmit,

C281x Hardware Interrupt

eCAN_A, eCAN_B

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