2.78 Periodic Interval Timer (PIT)

The Periodic Interval Timer (PIT) provides the operating system’s scheduler interrupt. It is designed to offer maximum accuracy and efficient management, even for systems with long response time.

20-bit Programmable Counter plus 12-bit Interval Counter
Reset-on-read Feature
Both Counters Work on Master Clock/16

Using The Library

PIT peripheral library can be used to poll for a periodic timeout, generate periodic interrupts or generate timed waits. The following examples shows different modes of its usage.

Polling method

int main ( void )
{
    int i;
    /* Initialize all modules */
    SYS_Initialize ( NULL );

    while ( true )
    {
        for (i=0; i<10; i++) {
            while(!PIT_TimerPeriodHasExpired());
            PIT_TimerRestart();
        }
        LED_BLUE_Toggle();
        /* Maintain state machines of all polled MPLAB Harmony modules. */
        SYS_Tasks ( );
    }

    /* Execution should not come here during normal operation */

    return ( EXIT_FAILURE );
}

Interrupt Method

static void pit_callback(uintptr_t context)
{
    (void)context;
    LED_BLUE_Toggle();
}

int main ( void )
{
    /* Initialize all modules */
    SYS_Initialize ( NULL );
    
    PIT_TimerCallbackSet(pit_callback, NULL);
    
    PIT_TimerStart();

    while ( true )
    {
        /* Maintain state machines of all polled MPLAB Harmony modules. */
        SYS_Tasks ( );
    }

    /* Execution should not come here during normal operation */

    return ( EXIT_FAILURE );
}

Delay routines

int main ( void )
{
    /* Initialize all modules */
    SYS_Initialize ( NULL );
    
    PIT_TimerCallbackSet(pit_callback, NULL);
    
    PIT_TimerStart();

    while ( true )
    {
        PIT_DelayMs(1000U);
        LED_BLUE_Toggle();
        /* Maintain state machines of all polled MPLAB Harmony modules. */
        SYS_Tasks ( );
    }

    /* Execution should not come here during normal operation */

    return ( EXIT_FAILURE );
}

Library Interface

Periodic Interval Timer peripheral library provides the following interfaces:

Functions


Name	Description
PIT_TimerInitialize	Initialize PIT registers per user configuration
PIT_TimerRestart	Restart the PIT counter
PIT_TimerStart	Start the PIT counter
PIT_TimerStop	Stop the PIT counter
PIT_TimerPeriodSet	Set the timer period value
PIT_TimerPeriodGet	Get the timer period value
PIT_TimerCounterGet	Get the timer counter value
PIT_TimerCompareSet	Set the timer comparison value
PIT_TimerFrequencyGet	Get the timer clock frequency
PIT_TimerPeriodHasExpired	Return whether or not the Timer Period has expired
PIT_DelayMs	Delays processing for x milliseconds
PIT_DelayUs	Delays processing for x microseconds
PIT_TimerCallbackSet	Register callback for PIT interrupt
PIT_ClearInterrupt	PIT Clear Interrupt

Data types and constants


Name	Type	Description
PIT_CALLBACK	Typedef	PIT Interrupt Callback Function definition

Note: Not all APIs maybe implemented. See the specific device family section for available APIs.