STM32F415xx bxCAN issue with transmit Frame and Recessive bit errors

[dirk23]

I am running CAN1 on a STM32F415 processor to communicate with an ECU and several other 415's on the bus. I have the SCE handler set up to store last error codes (LEC). I don't seem to be having any problems with the receive but the transmit side is getting frame and bit recessive errors. It happens every few seconds when I only have one module on the bus (5-6% bus loading) , but as I increase the modules and traffic (30-40% bus load), the TEC starts climbing and the higher addressed modules start getting into bus off range and must reset. I do have the bus properly terminated at each end and the ECU on the bus isn't having any issues.

-250kBps CAN speed

-Are the recessive errors due to being trumped by higher priority messages?

-Do the frame errors mean that my bus timing is slightly off?

I do have an oscilloscope and can look at outgoing messages from my device, but wasn't sure I would catch anything since it is intermittent at low traffic rates. I also have PCAN usb to can adapter to watch messages. I did hook up just the PCAN monitor and the module so they were the only things on the bus. It still gets occassional Tx errors.

[CAN Init Routine]

//*****************CAN 1 SETUP*********************
 	GPIO_InitTypeDef GPIO_InitStructure;
 	uint32_t filter_id, filter_mask;
 	filter_id=0x20000;
 	filter_mask=0x00000000;
  
	/* CAN1 Periph clock enable */
 	RCC_APB1PeriphClockCmd(RCC_APB1Periph_CAN1, ENABLE);
 	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);
  
	//GPIO setup
 	//CAN Setup CANRX
 	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
 	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
 	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
 	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
 	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
 	GPIO_Init(GPIOB, &GPIO_InitStructure);
  
 	//CAN Setup CANTX
 	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
 	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
 	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
 	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
 	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
 	GPIO_Init(GPIOB, &GPIO_InitStructure);
  
   //Connect GPIO pins to peripheral
   GPIO_PinAFConfig(GPIOB, GPIO_PinSource8, GPIO_AF_CAN1);
   GPIO_PinAFConfig(GPIOB, GPIO_PinSource9, GPIO_AF_CAN1);
  
 	// CAN1 register init
 	CAN_DeInit(CAN1);
  
 	CAN_StructInit(&CAN_InitStructure);
  
 	// CAN1 cell init
 	CAN_InitStructure.CAN_TTCM = DISABLE; // time-triggered communication mode = DISABLED
 	CAN_InitStructure.CAN_ABOM = DISABLE; // automatic bus-off management mode = DISABLED
 	CAN_InitStructure.CAN_AWUM = DISABLE; // automatic wake-up mode = DISABLED
 	CAN_InitStructure.CAN_NART = DISABLE; // non-automatic retransmission mode = DISABLED
 	CAN_InitStructure.CAN_RFLM = DISABLE; // receive FIFO locked mode = DISABLED
 	CAN_InitStructure.CAN_TXFP = DISABLE; // transmit FIFO priority = DISABLED
 	CAN_InitStructure.CAN_Mode = CAN_Mode_Normal;
  
 	CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;
 	CAN_InitStructure.CAN_BS1 = CAN_BS1_3tq;
 	CAN_InitStructure.CAN_BS2 = CAN_BS2_2tq;
  
 	// CAN1 Baudrate = 250kbps
 	// APB2 Clock is divided by 4, so 168/4=42MHz
 	// CAN_Prescaler value= CAN_clock/(required_Baudrate*total_number_of_tq)
 	// In present case, total_number_of_tq=CAN_SJW_1tq+CAN_BS1_3tq+CAN_BS2_2tq=6*tq
 	// so CAN_Prescaler= 42MHz/(250kbps*6)=28
 	CAN_InitStructure.CAN_Prescaler = 28;
  
  
 	if(CAN_Init(CAN1, &CAN_InitStructure)==CANINITOK)
 	{
  
 	}
  
  
 	filter_id= CAN_DEVICETYPEADDRESS;		 
	filter_mask=0X1FCC0000;			//This mask ignores the last 4 digits and bottom 2 bits of the 6th nibble
 
	uint16_t CAN_FilterIdHigh, CAN_FilterIdLow, CAN_FilterMaskIdHigh, CAN_FilterMaskIdLow;
	CAN_FilterIdHigh = ((filter_id & 0x07FF0000) >> 13) | ((filter_id & 0x0000FFFF) >> 13) ; // STID[10:0] & EXTID[17:13]
	CAN_FilterIdLow = ((filter_id & 0xFFFF) << 3) & 0xFFF8;                 // EXID[12:5] & 3 Reserved bits
	CAN_FilterMaskIdHigh = ((filter_mask & 0x07FF0000) >> 13) | ((filter_mask & 0x0000FFFF) >> 13) ;
	CAN_FilterMaskIdLow = ((filter_mask & 0xFFFF) << 3) & 0xFFF8;
 
	// CAN filter init
	CAN_FilterInitStructure.CAN_FilterNumber = 0;
	CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdMask;
	CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;
	CAN_FilterInitStructure.CAN_FilterIdHigh = CAN_FilterIdHigh;
	CAN_FilterInitStructure.CAN_FilterIdLow = CAN_FilterIdLow;
	CAN_FilterInitStructure.CAN_FilterMaskIdHigh = CAN_FilterMaskIdHigh;
	CAN_FilterInitStructure.CAN_FilterMaskIdLow = CAN_FilterMaskIdLow;
	CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FilterFIFO0;
	CAN_FilterInitStructure.CAN_FilterActivation = ENABLE;
	CAN_FilterInit(&CAN_FilterInitStructure);