Wrong clock configuration in FLEXCAN_Initialize

[mikhailburakov]

Hello community!

I've noticed strange behavior in FLEXCAN_Initialize. No matter what you pass as the last argument (clock source), this option is never applied. I performed a small investigation and found the reason for this. Prior to actually setting the clock source, softreset is issued to flexcan (kflexcan.c:325):

   if((can_reg_ptr->MCR & CAN_MCR_MDIS_MASK) == 0x00000000)
   {
      /* clock disable (module) */
      can_reg_ptr->MCR = CAN_MCR_MDIS_MASK;

      /* wait until disable mode acknowledged */
      while (!can_reg_ptr->MCR & CAN_MCR_LPMACK_MASK) {}
   }

   /* Reset FLEXCAN, Halt, freeze mode */
   if(FLEXCAN_Softreset(dev_num))
      return (FLEXCAN_INIT_FAILED);
  
   /*  Wait for entering the freeze mode */
   while((can_reg_ptr->MCR & CAN_MCR_FRZACK_MASK) == 0) {}
  
   /*
   ** Select the clock source
   ** Default: internal bus clock (fsys/2).
   */
   FLEXCAN_Select_clk (dev_num, clk);

In the FLEXCAN_Softreset, flexcan leaves "module disable" state. But according to K20 Sub-Family Reference Manual, clock source bit (CLKSRC of CANx_CTRL1) can be modified only in "module disable" state (p. 1112).

Best regards,

Mikhail Burakov

[AaronsCook]

Hi, Mikhail

I think the FlexCAN initialize steps just as follow code refer as the manual reference.

canx->MCR   |= CAN_MCR_MDIS_MASK; //disable CAN

canx->CTRL1 |= CAN_CTRL1_CLKSRC_MASK; // select the peripheral clock as clock source

//and the enable CAN and software reset

canx->MCR |= CAN_MCR_HALT_MASK;

canx->MCR |= CAN_MCR_FRZ_MASK;

canx->MCR &= ~CAN_MCR_MDIS_MASK;

while(!(canx->MCR & CAN_MCR_LPMACK_MASK));   

canx->MCR ^= CAN_MCR_SOFTRST_MASK;

while(canx->MCR & CAN_MCR_SOFTRST_MASK);

while(!(canx->MCR & CAN_MCR_FRZACK_MASK));

Best Regards

Laplenden

[mikhailburakov]

Hello!

Actually I don't have any problems with FlexCAN initialization. Just pointing out a quirk in MQX code, because someone can lose some time investigating this issue. The described behavior can be worked around with ease.

Best regards,

Mikhail Burakov