Can't retrieve extended CAN ID with ASTCanLib.h on AST-CAN485 Dev Board

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1

I’m attempting to read the CAN ID from a device that uses the CAN 29-bit extended frame format. The device manufacturer’s CAN utility (using SYS TEC CAN-to-USB dongle) returns an extended ID = 0780203C, and that matches the expected value from the documentation I have. However, using the ASTCanLib with the AST-CAN485 board, msg->id.ext and msg->id.std return the same value = 203C.

Without the entire ID I cannot distinguish between the two packet types (ID 0780203C and ID 0781203C) I need to read and parse.

Any help is much appreciated.

Code follows (simply-modified example from library):

/*
 * CAN port receiver example
 * Receives data on the CAN bus and prints to the serial port
 */

#include <ASTCanLib.h>              

#define MESSAGE_ID        0       // Message ID
#define MESSAGE_PROTOCOL  1       // CAN protocol (0: CAN 2.0A, 1: CAN 2.0B)
#define MESSAGE_LENGTH    8       // Data length: 8 bytes
#define MESSAGE_RTR       0       // rtr bit

// Function prototypes
void serialPrintData(st_cmd_t *msg);

// CAN message object
st_cmd_t Msg;

// Buffer for CAN data
uint8_t Buffer[8] = {};

void setup() {
  canInit(1000000);            // Initialise CAN port. Must be before Serial.begin
  Serial.begin(9600);       // start serial port
  Msg.pt_data = &Buffer[0];    // reference message data to buffer
  
  // Initialise CAN packet.
  // All of these will be overwritten by a received packet
  Msg.ctrl.ide = MESSAGE_PROTOCOL;  // Set CAN protocol (0: CAN 2.0A, 1: CAN 2.0B)
  Msg.id.ext   = MESSAGE_ID;        // Set message ID
  Msg.dlc      = MESSAGE_LENGTH;    // Data length: 8 bytes
  Msg.ctrl.rtr = MESSAGE_RTR;       // Set rtr bit
}

void loop() {
  // Clear the message buffer
  clearBuffer(&Buffer[0]);
  
  // Send command to the CAN port controller
  Msg.cmd = CMD_RX_DATA;
  
  // Wait for the command to be accepted by the controller
  while(can_cmd(&Msg) != CAN_CMD_ACCEPTED);
  // Wait for command to finish executing
  while(can_get_status(&Msg) == CAN_STATUS_NOT_COMPLETED);
  // Data is now available in the message object
  // Print received data to the terminal
  serialPrintData(&Msg);
}

void serialPrintData(st_cmd_t *msg){
  char textBuffer[80] = {0};

    sprintf(textBuffer,"id_ext %08X ",(msg->id.ext));
    Serial.print(textBuffer);
//    sprintf(textBuffer,"id_std %08X ",(msg->id.std));
//    Serial.print(textBuffer);

  //  IDE
  sprintf(textBuffer,"ide %d ",msg->ctrl.ide);
  Serial.print(textBuffer);


  //  RTR
  sprintf(textBuffer,"rtr %d ",msg->ctrl.rtr);
  Serial.print(textBuffer);
  
  //  DLC
  sprintf(textBuffer,"dlc %d ",msg->dlc);
  Serial.print(textBuffer);
  
  //  Data
  sprintf(textBuffer,"data ");
  Serial.print(textBuffer);
  
//  for (int i =0; i<msg->dlc; i++){
//    sprintf(textBuffer,"%02X ",msg->pt_data[i]);
//    Serial.print(textBuffer);

  for (int i =0; i<msg->dlc; i++){
    sprintf(textBuffer,"%02X ",msg->pt_data[i]);
    Serial.print(textBuffer);
  }
  Serial.print("\r\n");
}

Some output:

id_ext 0000203C ide 1 rtr 0 dlc 8 data 01 28 00 00 00 00 19 32 
id_ext 0000203C ide 1 rtr 0 dlc 8 data 00 C0 85 00 00 00 00 00 
id_ext 0000203C ide 1 rtr 0 dlc 8 data 00 C0 85 00 00 00 00 00 
id_ext 0000203C ide 1 rtr 0 dlc 8 data 00 C0 85 00 00 00 00 00 
id_ext 0000203C ide 1 rtr 0 dlc 8 data 00 C0 85 00 00 00 00 00 
id_ext 0000203C ide 1 rtr 0 dlc 8 data 01 28 00 00 00 00 19 32

data 01 28 00 00 00 00 19 32 messages have an extended ID = 0781203C

data 00 C0 85 00 00 00 00 00 messages have an extended ID = 0780203C

2

I think we both have the same problem. As I may be wrong, I’ll speak from my case. The data flows out fine but I can’t find what I’m looking for as I did not send an active request. It seem the examples for Rx & Tx need to be blended together. The Rx example has what looks like vesteges of Tx code, for example it sets MESSSAGE_ID but that buffer is immediately over written.

So we need to Tx the proper MESSAGE_ID to get back the data we want.

I have not yet found an example of request/responses using the CAN485 CAN bus and the ASTCanLib.h.

If anyone reading this thread has a working example of polling the CAN-bus it would be appreciated.

Thank You

3

I know I’m resurrecting a very old thread, but I had the exact same problem and didn’t find an answer anywhere on the interwebs. Hopefully this helps the next person who gets bit by this.

So, it turns out that the library is just fine. The problem is in the example code. For a standard ID (11 bits) it uses sprintf to print the ID formatted as “%04x” which works great. But, for an extended ID (29 bits), it uses sprintf to format it as “%d”. Why? Who knows? Of course, I changed that to “%08x” because I wanted to see it as hex, but I only ever got 16 bits worth of ID. (and, for that matter, even the %d format only returns 16 bits worth) The problem is that %d and %x take an “int” as an argument. In AVRland, “int” is 16 bits. (unlike in the 32 bit world, where it is usually 32 bits) The simple solution to make this work is to change that sprintf to “%lu” or, my preference, “%08lx”.