systick.c

#include "systick.h"

volatile uint32_t systickCount = 0;

// ******* Systick_init *******
// Initializes the SysTick interrupt timer.
//  Inputs: none
// Outputs: none
void Systick_init(void)
{
	// 48MHz int osc
	systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);

	// 48000000/100000 = 480 overflows per second - every 10 microseconds equals
	// one interrupt.
	// SysTick interrupt every N clock pulses: set reload to N-1 
	systick_set_reload(47900);
	systick_interrupt_enable();
	// Start counting
	systick_counter_enable();
}

// ******* Systick_timeGetCount *******
// Returns the elapsed program time based on the count of SysTick interrupts.
//  Inputs: none
// Outputs: A count of elapsed cycles.
uint32_t Systick_timeGetCount(void)
{
    return systickCount;
}

// ******* Systick_timeDelta *******
// Provides the difference between two program times, as provided by 
// Systick_get_time().
//  Inputs: A start time and an end time.
// Outputs: The delta between two points in execution time.
uint32_t Systick_timeDelta( uint32_t start, uint32_t end )
{
    uint32_t diff;

    // Detect if roll-over has occurred and calculate accordingly.
    if ( end > start )
    {
        diff = end - start;
    }
    else
    {
        diff = UINT32_MAX - ( start - end ) + 1;
    }

    return diff;
}

// ******* Systick_delayTicks *******
// Delays execution for x ticks based on time reporting from 
// Systick_get_time(). Scheduler event interrupt continues to fire.
//  Inputs: Number of ticks to delay execution.
// Outputs: none
void Systick_delayTicks( uint32_t wait_ticks )
{
	volatile uint32_t start, now, diff;

	start = Systick_timeGetCount();

	do
	{
		__asm__ __volatile__ ("nop");
		now = Systick_timeGetCount();
		
        diff = Systick_timeDelta( start, now );
	}
	while ( diff < wait_ticks );
}

// ******* sys_tick_handler *******
// Predefined SysTick ISR function with libopencm3 prototype. Runs the event
// manager and increments the counter.
//  Inputs: none
// Outputs: none
void sys_tick_handler(void)
{
	//Sched_runEventManager();

	// Roll over to 0 at UINT32_MAX
	if ( systickCount < UINT32_MAX )
	{
		systickCount++;
	}
	else
	{
		systickCount = 0;
	}

}