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.