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jungle_jim
Visitor II
March 10, 2024
Solved

F446RE and CAN2 in loopback mode

  • March 10, 2024
  • 1 reply
  • 2469 views

I'm working on a custom board with a F446RET6 and testing through some code bits. I've been able to successfully test that the board programs and functions with a led-blink style program. My problem is that I'm attempting to use CAN2; I'm trying to test via loopback but I'm having issues getting any type of IRQ for a receive. I feel like its something basic I'm missing here but after reading through some other posts I'm either brain-dead or missing something.

  • currently using the HSI clock but I wouldn't think that would matter for loopback testing (understand for the "real" thing would be best to use the HSE).
  • RX GPIO is set to pull-up
  • Verified (after looking at some old posts using an older version of Cube) that the CAN1 clock is being initialized

Also I understand that the "CAN2" device is really the "slave" to CAN1. I've got my slave start for the filter set to 14 to split everything half and half and just arbitrarily chose bank 15:

 

 

 

hcan2Filter.FilterActivation = ENABLE;
hcan2Filter.FilterIdHigh = 0x0000;
hcan2Filter.FilterIdLow = 0x0000;
hcan2Filter.FilterMaskIdHigh = 0x0000;
hcan2Filter.FilterMaskIdLow = 0x0000;
hcan2Filter.FilterMode = CAN_FILTERMODE_IDMASK;
hcan2Filter.FilterScale = CAN_FILTERSCALE_32BIT;
hcan2Filter.FilterFIFOAssignment = CAN_RX_FIFO1;
hcan2Filter.FilterBank = 15;
hcan2Filter.SlaveStartFilterBank = 14;

 

 

 

 

Also I have the FIFO1 message pending interrupt set up:

 

 

 

//enable CAN2 interrupt
if (HAL_CAN_ActivateNotification(&hcan2, CAN_IT_RX_FIFO1_MSG_PENDING) != HAL_OK)
{
 printf("CAN IRQ enable error\r\n");
 Error_Handler();
}

 

 

 

 

The IRQ function for now just spits out the rx'd ID:

 

 

 

void HAL_CAN_RxFifo1MsgPendingCallback(CAN_HandleTypeDef *hcan)
{
 if (HAL_CAN_GetRxMessage(hcan, CAN_RX_FIFO1, &RxHeader, RxData) != HAL_OK)	//get can message
 {
 printf("CAN msg RX error\r\n");
 Error_Handler();
 }										//handle any errors if not OK
 printf("CAN Message Rx'd from ID %d\r\n", RxHeader.StdId);
 return;
}

 

 

 

 

I've attached my IOC and main, can someone point out what's probably staring me in the face?

    This topic has been closed for replies.
    Best answer by jungle_jim

    Yes, I understand how to adjust the CAN timing. My question was on if the CAN-TX pin (PB13) is still exposed in loopback or not. I thought I remembered coming across that it was.

     

    For anyone that comes across this with google, the latest ioc managed to pass loopback after updating the mode. I think when I re-wrote the code I had it and was just fighting a few different things. Some good threads out there explaining better the filtering and banks.

     

    Filter banks explained 

    Filter slave start address 

     

    Some other things that tripped me up which i guess was just a cumulative mess:

    • One thing that I guess when I started wasn't abundantly clear is that you HAVE to set the filter, even if its "let everything through" so the RX data gets assigned to a FIFO.
    • See above for the filter setup. If you're using CAN1, you have to select a bank BELOW the "slave start filter bank" address. If you're using CAN2, you have to select a bank ABOVE the "slave start" address.
    • Remember "rx0 interrupt" and "rx1 interrupt" in the NVIC settings correspond to fifo0 and fifo1, respectively.
    • Remember you can setup the rx data to go to either Fifo0 OR Fifo1, no matter which CAN peripheral you're using. Just make sure the IRQ hook and callback are set appropriately (based on your filter configuration).

    1 reply

    M
    mƎALLEm
    Technical Moderator
    March 11, 2024

    Hello,

    Checking your code, you are configuring the CAN in normal mode not in loopback mode.

    J
    jungle_jimAuthor
    Visitor II
    March 12, 2024

    Valid. I had tried to update the same code prior for CAN1 and was having the same issues, I missed that in reverting back. Updated the OP to make clear. Changing to loopback still results in the same issue.

    Speaking of loopback, so long as its in "loopback" but not "loopback + silent" the TX pin (PB13) should still be exposed, correct? I'll see if I can slow the bitrate down to something my "dumb" logic analyzer can pick up or not just to test if there's anything getting out at all.

    M
    mƎALLEm
    Technical Moderator
    March 12, 2024

    Hello,

    Try to change the following parameters' values:

     

     hcan2.Init.Prescaler = 12;
 hcan2.Init.TimeSeg1 = CAN_BS1_3TQ;
 hcan2.Init.TimeSeg2 = CAN_BS2_1TQ;

     

    Decrease, the prescaler as much as possible and increase BS1 and BS2 as much as possible to fit your bitrate.  

    Try for example:

    Prescaler = 3

    BS1 = 14

    BS2 = 5

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