Timer2 period match interrupt on dsPIC33F not working

Question

I'm trying to get the Timer2 period match interrupt on my dsPIC33FJ128GP802 working. I want it to interrupt after ~480 cycles. I'm using MPLAB C30.

I have, to initialize the timer and interrupt:

// Initialize Timer2, which is used for output timing.
T2CONbits.TON = 1;
T2CONbits.TSIDL = 0;
T2CONbits.TCKPS = 0;
T2CONbits.TCS = 0;
T2CONbits.T32 = 0;
// Initialize Timer2 interrupt with a slightly
// higher priority.
IPC1bits.T2IP = 5;
IFS0bits.T2IF = 0;
IEC0bits.T2IE = 0;

(the timer interrupt is initially disabled)

I have already got pin change interrupts working with a priority of 4. I want the Timer2 interrupt to have a higher priority.

And to set up the interrupt I have this:

T2CONbits.TON = 1;
TMR2 = 0;
timer2_osd = 480 + vid_hoffset;
PR2 = timer2_osd;
IEC0bits.T2IE = 1;

I also have an ISR,

void _MY_ISR _T2Interrupt()
{
    IFS0bits.T2IF = 0;
    return;
}

However I find the processor just resets and will not run with this enabled. It will work with a busy loop checking the timer, but that wastes cycles.

Can anyone see where I've gone wrong?

Answer 1

I just looked at the code I wrote a while ago to set up timer 2 for a periodic interrupt of 1 ms for a PIC24F (essentially same timer hardware as dsPIC33F), and it looks like so:

#define CPU_CLK_RATE 32000000L
#define PERIPH_CLOCK_RATE (CPU_CLK_RATE/2L)

#define TIMER_2_RATE 1000L
#define TIMER_2_PRE  64L        // clock rate is (32000000/2)/64 = 250 KHz
#define TIMER_2_MATCH (PERIPH_CLOCK_RATE/(TIMER_2_RATE * TIMER_2_PRE))  

    T2CON = 0; // set control register to defaults

    T2CONbits.TSIDL = 1;  // discontinue when idle
    T2CONbits.TCKPS1 = 1; // prescaler of 64
    T2CONbits.TCKPS0 = 0; // prescaler of 64
    T2CONbits.T32 = 0;    // 16 bit timer
    T2CONbits.TCS = 0;    // FOSC/2 (32Mhz/2)
    TMR2 = 0-TIMER_2_MATCH*19;  // 20 millisecond delay before starting
    PR2 = TIMER_2_MATCH; 

    SetPriorityIntT2(TIMER2_INTERRUPT_PRIORITY); // set to very high priority
    EnableIntT2; // enable interrupts

    T2CONbits.TON = 1

Very similar to yours, except I pre-initialized TMR2 so there would be a delay before the first interrupt. Don't know if that would help in your case or not, but you might try it.

Answer 2

The datasheet seems to suggest you should clear TON, initialize the timer, then set TON. Many example sequences end with setting TON, they don't start with it.

Many devices latch working values out of their configuration registers when they're enabled... so you should always disable, configure, then enable. Be very careful when changing registers on a running peripheral.

I'm also not clear on how the interrupt code gets tied to the timer2 interrupt event. What's _MY_ISR?