#include "project.h"

#define  SPURIOUS	MS(10) /*Anything faster than 6000rpm is a false trigger */



uint32_t raw_tacho;

static uint32_t
cycle_diff (uint32_t a, uint32_t b)
{
  return b - a;
}



void exti3_isr (void)
{
uint32_t now, diff;
static uint32_t last_edge;

if (!( EXTI_PR & TACHO)) return;

EXTI_PR=TACHO;

now=dwt_read_cycle_counter();

diff= cycle_diff(last_edge,now);

if (diff < SPURIOUS) return;

last_edge=now;


/* Want RPM, diff is in units of 1/72 us */

if (!diff) return;

/* uint32_t is able to express 60s in clock ticks, so divide everything by 2 */

diff >>=1;


	
raw_tacho =(US ((60*1000000)/2))/diff;

}


void tacho_init (void)
{
  MAP_INPUT_PU (TACHO);

  exti_select_source (TACHO,TACHO_PORT);
  exti_set_trigger (TACHO, EXTI_TRIGGER_FALLING);
  exti_enable_request (TACHO);
  exti_reset_request (TACHO);

  nvic_enable_irq (TACHO_IRQ);

}