//------------------------------------------------------------------------------
/// Handler for PIT interrupt. Increments the timestamp counter.
//------------------------------------------------------------------------------
void ISR_Pit(void)
{
unsigned int status;

// Read the PIT status register
status = PIT_GetStatus() & AT91C_PITC_PITS;
if (status != 0) {
// 1 = The Periodic Interval timer has reached PIV since the last read of PIT_PIVR.
// Read the PIVR to acknowledge interrupt and get number of ticks
//Returns the number of occurrences of periodic intervals since the last read of PIT_PIVR.
timestamp += (PIT_GetPIVR() >> 20);
}
}

//------------------------------------------------------------------------------
/// Configure the periodic interval timer (PIT) to generate an interrupt every
/// millisecond.
//------------------------------------------------------------------------------
void ConfigurePit(void)
{
// Initialize the PIT to the desired frequency
PIT_Init(PIT_PERIOD, BOARD_MCK / 1000000);

// Configure interrupt on PIT
IRQ_DisableIT(AT91C_ID_SYS);
IRQ_ConfigureIT(AT91C_ID_SYS, AT91C_AIC_PRIOR_LOWEST, ISR_Pit);
IRQ_EnableIT(AT91C_ID_SYS);
PIT_EnableIT();

// Enable the pit
PIT_Enable();
}

//------------------------------------------------------------------------------
/// Waits for the given number of milliseconds (using the timestamp generated
/// by the SAM7 & SAM9 microcontrollers's PIT, or SAM3's microcontrollers's system tick).
/// \param delay Delay to wait for, in milliseconds.
//------------------------------------------------------------------------------
void Wait(unsigned long delay)
{
volatile unsigned int start = timestamp;
unsigned int elapsed;
do {
elapsed = timestamp;
elapsed -= start;
}
while (elapsed < delay);
}

-- Getting Started Project 1.9-rc1 --
-- AT91SAM9M10-EK
-- Compiled: Apr 27 2010 15:51:38 --
-I- configure pit.