AnsweredAssumed Answered

CAN loopback very weird problem

Question asked by yao.randy.001 on Oct 10, 2014
Latest reply on Oct 11, 2014 by Mark Edwards
Hi ST forums,

I wrote a piece of code to try out CAN_TX and CAN_RX to loopback the data into from PD1 (CAN1_TX) into PD0 (CAN1_RX). It seems to be working (I get back what I sent). Then I realized even if I unplug the jumper from PD0 to PD1 it is still receiving CAN data, (Receive LED on, data streaming in).

Is TxMessage.Data connected to RxMessage.Data? Please take a look:




#include "stm32f4xx_gpio.h"
#include "stm32f4xx_rcc.h"
#include "stm32f4xx_can.h"
#include "misc.h"
#include "semihosting.h"

GPIO_InitTypeDef  GPIO_InitStructure;
CAN_InitTypeDef        CAN_InitStructure;
CAN_FilterInitTypeDef  CAN_FilterInitStructure;
NVIC_InitTypeDef  NVIC_InitStructure;
CanTxMsg TxMessage;
CanRxMsg RxMessage;


void CAN_Config(void);
void NVIC_Config(void);


void CAN_Config(void)
{
  /* Enable GPIO clock */
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_CAN1, ENABLE);


  /* Connect CAN pins to AF9 */
  GPIO_PinAFConfig(GPIOD, GPIO_PinSource0, GPIO_AF_CAN1);
  GPIO_PinAFConfig(GPIOD, GPIO_PinSource1, GPIO_AF_CAN1);


  /* Configure CAN RX and TX pins */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_UP;
  GPIO_Init(GPIOD, &GPIO_InitStructure);


  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
  GPIO_Init(GPIOD, &GPIO_InitStructure);


  //CAN1
  /* CAN register init */
  CAN_DeInit(CAN1);


  /* CAN cell init */
  CAN_DBGFreeze(CAN1, DISABLE);
  CAN_InitStructure.CAN_TTCM = DISABLE;
  CAN_InitStructure.CAN_ABOM = DISABLE;
  CAN_InitStructure.CAN_AWUM = DISABLE;
  CAN_InitStructure.CAN_NART = DISABLE;
  CAN_InitStructure.CAN_RFLM = DISABLE;
  CAN_InitStructure.CAN_TXFP = DISABLE;
  CAN_InitStructure.CAN_Mode = CAN_Mode_LoopBack;
  CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;
  CAN_InitStructure.CAN_BS1 = CAN_BS1_14tq;
  CAN_InitStructure.CAN_BS2 = CAN_BS2_6tq;
  CAN_InitStructure.CAN_Prescaler = 200; //CAN baud rate 10kbits
  CAN_Init(CAN1, &CAN_InitStructure);


  /* 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 = 0x0000;
  CAN_FilterInitStructure.CAN_FilterIdLow = 0x0000;
  CAN_FilterInitStructure.CAN_FilterMaskIdHigh = 0x0000;
  CAN_FilterInitStructure.CAN_FilterMaskIdLow = 0x0000;
  CAN_FilterInitStructure.CAN_FilterFIFOAssignment = 0;
  CAN_FilterInitStructure.CAN_FilterActivation = ENABLE;
  CAN_FilterInit(&CAN_FilterInitStructure);


  /* Transmit Structure preparation */
  TxMessage.StdId = 0x321;
  TxMessage.ExtId = 0x00;
  TxMessage.RTR = CAN_RTR_DATA;
  TxMessage.IDE = CAN_ID_STD;
  TxMessage.DLC = 1;


  TxMessage.Data[0] = 0x55;


  /* Enable FIFO 0 message pending Interrupt */
  CAN_ITConfig(CAN1, CAN_IT_FMP0, ENABLE);
}


void NVIC_Config(void)
{
  NVIC_InitStructure.NVIC_IRQChannel = CAN1_RX0_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
}


void Init_RxMes(CanRxMsg *RxMessage)
{
  uint8_t i = 0;


  RxMessage->StdId = 0x00;
  RxMessage->ExtId = 0x00;
  RxMessage->IDE = CAN_ID_STD;
  RxMessage->DLC = 8;
  RxMessage->FMI = 0;


  for (i = 0;i<8;i++)
  {
    RxMessage->Data[i] = 0x00;
  }
}


int main(void)
{
  CAN_Config();
  NVIC_Config();
  Init_RxMes(&RxMessage);
  /* Infinite loop */
  while (1)
  {
    CAN_Transmit(CAN1, &TxMessage);
    printf("\nData Received (0): %X",RxMessage.Data[0]);
//  printf("\nData Received (1): %d",RxMessage.Data[1]);
//  printf("\nData Received (2): %d",RxMessage.Data[2]);
//  printf("\nData Received (3): %d",RxMessage.Data[3]);
//  printf("\nData Received (4): %d",RxMessage.Data[4]);
//  printf("\nData Received (5): %d",RxMessage.Data[5]);
//  printf("\nData Received (6): %d",RxMessage.Data[6]);
//  printf("\nData Received (7): %d",RxMessage.Data[7]);
  }
}


void CAN1_RX0_IRQHandler(void)
{
  CAN_Receive(CAN1, CAN_FIFO0, &RxMessage);
  GPIOD->BSRRL = GPIO_Pin_12;
}

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