How to read identifier(ID) of each CAN message

Hi Shawn,

using IF1ARB or IF2ARB is the right approach to read out the CAN message IDs. However to be able to read it out from those registers you need to setup a read transfer from the message RAM into the IF1ARB or IF2ARB register for the message object which you are using. Please see the the section "24.6.2 Using Message Interface Register Sets 1 and 2" in the TRM for details.

Best regards

Andreas

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Hi Andreas,

Thank you for your reply, I managed to solve the problem. I set IF3UpdEn register to allow automatically update of all messages, and by reading IF3ARB and IF3Datax, it works.

Thanks,

Shawn

Hi,

I'm having the same problem as Shawn. I've tried to implement the access you described for IF1ARB/IF2ARB but I'm not having a great deal of success.

Can you post a fragment of code in here that does an ARB register read, so I can see where I'm going wrong?

Thanks

Andy

Hello Andy,

in order to read the IFxARB register you need to setup a read transfer from the message RAM to the IFx registers.
Therefore in IFxCMD:

- Bit 23 WR/RD: 0 -> Read
- Bit 21 Arb: 1-> transfer arbitration bits
- Write message object number into bits 7:0 to trigger the transfer.
- Check bit 15 (busy) to see when the transfer is finished.

Best regards

Andreas

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Hi Andreas,

I believe the code fragment below does what you described:

void CAN2_RX_Unload_Rx_Msg(U8 fifo_buff_num_u8)
{
    U16 can_id_u16;
    U32 can_id_u32;
    U8  rx_buffer_u8;
    U32 ExtendedID_u32;
    U32 Status;
    
    
    while (canREG2->IF2STAT & 0x80U){}  // wait until IF registers are free
    canREG2->IF2CMD = 0x23;             // bits 23 = 0, 21 = 1, 17&16 = 1 (RD, ARB, DATA A & DATA B)
    canREG2->IF2NO   = fifo_buff_num_u8;
    
    while (canREG2->IF2STAT & 0x80U){}  // wait until IF registers are free
    ExtendedID_u32 = canREG2->IF2ARB;
    
There is only one message being transmitted from CAN1 and received by CAN2. That message has an ID of 0x400. 

DCAN2->NEWDATX = 0x00000001 and DCAN2->NEWDAT12 = 0x00000001, indicating message box 1 contains the new message.

fifo_buff_num_u8 = 1, but the value read into ExtendedID_u32 is 0x90000000 rather than the expected 0x400.

What have I missed?

Regards

Andy

Hi Andy,

looks like you are working with standard 11-bit IDs, then the ID 0x400 is correctly represented in the IFxARB register with the value you have give above. Please note that in standard ID mode the ID bits are IFxARB[28:18].

Best regards

Andreas

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