IMXRT1176 CAN peripheral behaves as if Loop back enabled

[burhanhagi]

I have two CANs used in my PCB. CAN1, CAN3.

I am using message buffers for TX and RX.  

#define RX_MESSAGE_BUFFER_NUM (9)

#define TX_MESSAGE_BUFFER_NUM (8)

#define USE_CANFD (0)

** I am trying to take any Classical Standard or Extended CAN message with interrupt and send it back with +1 increment for coming id and each received can data. 

** I am using interrupt for only receiving. For transmitting, I do not use interrupt. I sent it with "FLEXCAN_WriteTxMb" non blocking- method.

** Even though I am sending only one time, FLEXCAN sends continously data. I disabled "loopback" disabled at init procedure. However, it behaves as I stated.

Here is my simple code important areas :

/*

#define EXAMPLE_CAN CAN1

#define EXAMPLE_FLEXCAN_IRQn CAN1_IRQn

#define EXAMPLE_FLEXCAN_IRQHandler CAN1_IRQHandler

*/

#define EXAMPLE_CAN CAN3

#define EXAMPLE_FLEXCAN_IRQn CAN3_IRQn

#define EXAMPLE_FLEXCAN_IRQHandler CAN3_IRQHandler

void EXAMPLE_FLEXCAN_IRQHandler(void){

uint64_t flag = 1U;

if (0U != FLEXCAN_GetMbStatusFlags(EXAMPLE_CAN, flag << RX_MESSAGE_BUFFER_NUM))

{

FLEXCAN_ClearMbStatusFlags(EXAMPLE_CAN, flag << RX_MESSAGE_BUFFER_NUM);

(void)FLEXCAN_ReadRxMb(EXAMPLE_CAN, RX_MESSAGE_BUFFER_NUM, &rxFrame);

rxComplete = true;

}

SDK_ISR_EXIT_BARRIER;

}

flexcan_config_t flexcanConfig;

flexcan_rx_mb_config_t mbConfig;

clock_root_config_t rootCfg = {0};

rootCfg.mux = FLEXCAN_CLOCK_SOURCE_SELECT;

rootCfg.div = FLEXCAN_CLOCK_SOURCE_DIVIDER;

/* CLOCK_SetRootClock(kCLOCK_Root_Can1, &rootCfg);*/

CLOCK_SetRootClock(kCLOCK_Root_Can3, &rootCfg);

FLEXCAN_GetDefaultConfig(&flexcanConfig);

flexcanConfig.bitRate = 250000U;

flexcanConfig.enableLoopBack = false;

FLEXCAN_Init(EXAMPLE_CAN, &flexcanConfig, EXAMPLE_CAN_CLK_FREQ);

mbConfig.format = kFLEXCAN_FrameFormatExtend;

mbConfig.type = kFLEXCAN_FrameTypeData;

mbConfig.id = FLEXCAN_ID_EXT(0x00000000);

FLEXCAN_SetRxMbConfig(EXAMPLE_CAN, RX_MESSAGE_BUFFER_NUM, &mbConfig, true);

FLEXCAN_SetTxMbConfig(EXAMPLE_CAN, TX_MESSAGE_BUFFER_NUM, true);

FLEXCAN_EnableMbInterrupts(EXAMPLE_CAN, flag << RX_MESSAGE_BUFFER_NUM);

(void)EnableIRQ(EXAMPLE_FLEXCAN_IRQn);

while (true)

{

rxComplete = false;

while (!rxComplete)

{

}

rxFrame.id = FLEXCAN_ID_EXT(rxFrame.id) + 0x01;

rxFrame.dataByte0 += 1;

rxFrame.dataByte1 += 1;

rxFrame.dataByte2 += 1;

rxFrame.dataByte3 += 1;

rxFrame.dataByte4 += 1;

rxFrame.dataByte5 += 1;

rxFrame.dataByte6 += 1;

rxFrame.dataByte7 += 1;

if (kStatus_Success == FLEXCAN_WriteTxMb(EXAMPLE_CAN, TX_MESSAGE_BUFFER_NUM, &rxFrame))

{;}

** I have one data logger with sending capability. I am also using debugger to find the problem. What I see is that; as soon as I send such as 0x18aabbcc id message, it produces continously interrupt and that is why I am taking 0x18aabbcd, 0x18aabbce, 0x18aabbcf... 

** I read with debugger in interrupt handler, there is always "1" in RX_MESSAGE_BUFFER_NUM place in  IFLAG register. So it continously produces interrupt. I do not understand where I am missing?

[burhanhagi]

Hi @PetrS, I see the you replied most questions on FLEXCAN for MPC and S32 series. I am using IMXRT1176 but thinks flexcan structure is similiar. Can you please help me my above issue regarding CAN?

Thank you

[PetrS · Accepted solution]

Hi,

exact setting is hidden here, but it seems you can have self-reception enabled. Check MCR[SRXDIS] bit.

BR, Petr

[burhanhagi]

Many thanks @PetrS for your very quick response. 

You are right. MCR[SRXDIS]  was 0 means self reception enabled.

After your guide, I noticed that disableSelfReception flag controls SRXDIS bit. After changing it, everything now works as accepted. Thanks a lot again.

flexcanConfig.enableLoopBack = false;

flexcanConfig.disableSelfReception =true;