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#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);
}
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