STM32 CAN Filtering

[akshayamk]

Posted on January 20, 2016 at 01:53

Hello!

I have configured my filter banks. However, the standard ID that the receive FIFO0 register is reading after controller transmits a response to my module is not what I expect. Hence, I suspect this phenomenon is due to incorrect message filtering that causes an incorrect bit sequence to be stored in the receive FIFO0 register. The following is my code:

CAN_FilterConfTypeDef CAN_FilterConfig[5] = { 
{.BankNumber = 0, .FilterActivation = ENABLE, .FilterNumber = 0, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdLow = (0x7FF << 5), .FilterMaskIdHigh = 0, 
.FilterIdLow = (STID1 << 5), .FilterIdHigh = 0}, 
{.BankNumber = 0, .FilterActivation = ENABLE, .FilterNumber = 1, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdHigh = (0x7FF << 5), .FilterMaskIdLow = 0, 
.FilterIdHigh = (STID2 << 5), .FilterIdLow = 0}, 
{.BankNumber = 0, .FilterActivation = ENABLE, .FilterNumber = 2, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdLow = (0x7FF << 5), .FilterMaskIdHigh = 0, 
.FilterIdLow = (STID3 << 5), .FilterIdHigh = 0}, 
{.BankNumber = 0, .FilterActivation = ENABLE, .FilterNumber = 3, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdHigh = (0x7FF << 5), .FilterMaskIdLow = 0, 
.FilterIdHigh = (STID4 << 5), .FilterIdLow = 0}, 
{.BankNumber = 0, .FilterActivation = ENABLE, .FilterNumber = 4, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdHigh = 0, .FilterMaskIdLow = (0x7FF << 5), 
.FilterIdHigh = 0, .FilterIdLow = (STID5 << 5)}, 
}; 
HAL_CAN_ConfigFilter(&hcan, &CAN_FilterConfig[0]); 
HAL_CAN_ConfigFilter(&hcan, &CAN_FilterConfig[1]); 
HAL_CAN_ConfigFilter(&hcan, &CAN_FilterConfig[2]); 
HAL_CAN_ConfigFilter(&hcan, &CAN_FilterConfig[3]); 
HAL_CAN_ConfigFilter(&hcan, &CAN_FilterConfig[4]);

I have configured 5 messages in the filters using filter numbers 0 to 4. Is this configuration correct? Is this what determines what is stored in the can receive FIFIO 0 (CAN_RIXR) register? FYI, I am using a STM32F302 custom made board. Thank you!

[Tesla DeLorean]

Posted on January 20, 2016 at 05:34

The basic problem here is one of not understanding 16-bit filters. You basically split the 32-bit comparator in two so that each entry represents two independent filters, one in the low word, and the other in the high word. By defining the high mask/match as zero you've created a test that passes everything.

ie ((X & 0) == 0), is always true, thus all cases pass As I understand it, you'd pack two filters in each entry like this

{.BankNumber = 0, .FilterActivation = ENABLE, .FilterNumber = 0, .FilterFIFOAssignment = 0,
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdLow = (0x7FF << 5), .FilterMaskIdHigh = (0x7FF << 5), 
.FilterIdLow = (STID1 << 5), .FilterIdHigh = (STID2 << 5)},

[akshayamk]

Posted on January 21, 2016 at 01:26

Hi Clive,

Thanks a lot for your reply. I have amended my code to this:

CAN_FilterConfTypeDef CAN_FilterConfig[3] = { 
{.BankNumber = 0, .FilterActivation = ENABLE, .FilterNumber = 0, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdLow = (0x7FF << 5), .FilterMaskIdHigh = (0x7FF << 5), 
.FilterIdLow = (STID1 << 5), .FilterIdHigh = (STID2 << 5)}, 
{ .FilterActivation = ENABLE, .FilterNumber = 1, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_16BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdLow = (0x7FF << 5), .FilterMaskIdHigh = (0x7FF << 5), 
.FilterIdLow = (STID3 << 5), .FilterIdHigh = (STID4 << 5)}, 
{ .FilterActivation = ENABLE, .FilterNumber = 2, .FilterFIFOAssignment = 0, 
.FilterScale = CAN_FILTERSCALE_32BIT, .FilterMode = CAN_FILTERMODE_IDMASK, 
.FilterMaskIdLow = 0, .FilterMaskIdHigh = (0x7FF << 5), 
.FilterIdLow = 0, .FilterIdHigh = (STID5 << 5)}, 
};

I am able to receive message properly for one type of message (ie STID3) but I expect to also receive STID2 message but I am not able to receive STID2 message.