My code tries to configure the CAN device, but it never leaves configuration mode. Why?

Question

I'm using a PIC32MX534F064L, and I just started working with the CAN module. The first thing I tried was using the examples from Microchip. None of them worked. The basic problem is these lines:

CANSetOperatingMode(CAN1, CAN_NORMAL_OPERATION);
while(CANGetOperatingMode(CAN1) != CAN_NORMAL_OPERATION);

The while on the second line never completes.

I'll explain. The PIC32's CAN module has to be configured in the following order:

1. Enable the CAN module.
2. Switch the CAN module to "configuration" operation mode.
3. Configure the CAN module.
4. Switch CAN module to "normal" operation mode.

Step 2 and 4 are a little more complicated. Instead of just setting a register which would change the mode, there's a two-step process. You set a register (C1CON.REQOP) to request that the operation mode (C1CON.OPMOD) will change, and when the CAN module is ready to change, it does.

Anyway, here is the code. I'm sure I just forgot something, but scouring the Internet and trying various examples has been without result.

#include <plib.h>

#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF
#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_1

#define SYS_FREQ (80000000L)
#define CAN_BUS_SPEED 250000

BYTE CAN1MessageFifoArea[2 * 8 * 16];

int main(void)
{
    CAN_BIT_CONFIG canBitConfig;
    CAN_OP_MODE mode;
    int i;

    SYSTEMConfig(SYS_FREQ, SYS_CFG_WAIT_STATES | SYS_CFG_PCACHE);

    CANEnableModule(CAN1,TRUE);
    while(C1CONbits.ON == 0);
    CANSetOperatingMode(CAN1, CAN_CONFIGURATION);
    while(CANGetOperatingMode(CAN1) != CAN_CONFIGURATION);

    canBitConfig.phaseSeg2Tq            = CAN_BIT_3TQ;
    canBitConfig.phaseSeg1Tq            = CAN_BIT_3TQ;
    canBitConfig.propagationSegTq       = CAN_BIT_3TQ;
    canBitConfig.phaseSeg2TimeSelect    = TRUE;
    canBitConfig.sample3Time            = TRUE;
    canBitConfig.syncJumpWidth          = CAN_BIT_2TQ;
    CANSetSpeed(CAN1,&canBitConfig,SYS_FREQ,CAN_BUS_SPEED);

    CANAssignMemoryBuffer(CAN1,CAN1MessageFifoArea,(2 * 8 * 16));

    CANConfigureChannelForTx(CAN1, CAN_CHANNEL0, 8,
                             CAN_TX_RTR_DISABLED, CAN_LOW_MEDIUM_PRIORITY);
    CANConfigureChannelForRx(CAN1, CAN_CHANNEL1, 8,
                             CAN_RX_FULL_RECEIVE);

    CANConfigureFilter      (CAN1, CAN_FILTER0, 0x8004001, CAN_EID);
    CANConfigureFilterMask  (CAN1, CAN_FILTER_MASK0, 0x3FFFFFFF,
                             CAN_EID, CAN_FILTER_MASK_IDE_TYPE);
    CANLinkFilterToChannel  (CAN1, CAN_FILTER0, CAN_FILTER_MASK0, CAN_CHANNEL1);
    CANEnableFilter         (CAN1, CAN_FILTER0, TRUE);

    CANEnableChannelEvent(CAN1, CAN_CHANNEL1, CAN_RX_CHANNEL_NOT_EMPTY, TRUE);
    CANEnableModuleEvent(CAN1, CAN_RX_EVENT, TRUE);

    // The code gets stuck in the while and never finishes.
    C1CONbits.CANBUSY = 1;
    CANSetOperatingMode(CAN1, CAN_NORMAL_OPERATION);
    while(CANGetOperatingMode(CAN1) != CAN_NORMAL_OPERATION);

    // This code is never reached
    i=0;
    while(1)
        ++i;
}

Answer 1

Well, it turned out that if you connect a CAN transceiver to the CAN pins on the PIC, but fail to supply it with power, then the PIC never leaves configuration mode. Connecting the transceiver to a reliable power source solved the problem.

Answer 2

Here's an interesting one on a PIC18F-Q chip (PIC18F26Q84 to be exact). Code kept hanging when trying to exit CAN BUS Configuration with CANTX on RB2, CANRX on RB3. Code would NOT hang when changing the CAN Bus RX input from RB3 to some other input pin. Just trying to read RB3 as a digital input always came back as 0 even when set as a regular digital input pin and feeding 3.3V into it. The solution? TURN OFF JTAG Boundary Scan in CONFIG2. Update: At this point in time, the documentation and MCC for the PIC18F26Q84 incorrectly configures C1FIFOBA = 0x3800. That's great for the PIC18F27Q84 but the PIC18F26Q84 works a lot better with C1FIFOBA = 0x2600;