1 files changed, 32 insertions, 4 deletions
diff --git a/table-fan/table-fan.c b/table-fan/table-fan.c
index 2cf9a32..0a49c91 100644
--- a/table-fan/table-fan.c
+++ b/table-fan/table-fan.c
@@ -65,6 +65,37 @@ inline void pwm_dec(void)
     PWM_VAL--;
 }
 
+
+void tacho_init(void)
+{
+  DDRD &= ~(1<<PD4);
+  PORTD |= (1<<PD4);
+  TCCR1B = 0; // make sure timer is stopped
+
+  TCCR1A = 0;
+  TCNT1 = 0;
+  TIMSK1 = (1<<ICIE1);
+
+  TCCR1B = (1<<CS12); // start timer
+}
+
+ISR(TIMER1_CAPT_vect)
+{
+  static uint16_t tacho_last_ts = 0;
+  uint16_t current = ICR1;
+  uint16_t diff = 0;
+  if(current > tacho_last_ts) {
+    diff = current - tacho_last_ts;
+  } else {
+    diff = (UINT16_MAX - tacho_last_ts) + current;
+  }
+  tacho_last_ts = current;
+
+  float rpm = 1875000.0 / (float)diff ;
+  printf("\rtacho: %8.2f rpm", rpm);
+}
+
+
 void handle_cmd(uint8_t cmd)
 {
   switch(cmd) {
@@ -89,12 +120,9 @@ int main(void)
   led_init();
   usbio_init();
   pwm_init();
+  tacho_init();
   sei();
 
-      // FAN tacho input (enable Pull-Up)
-  DDRD &= ~(1<<PD4);
-  PORTD |= (1<<PD4);
-
       // rotary encoder
   DDRB &= ~((1<<PB4) | (1<<PB5));
   PORTB |= (1<<PB4) | (1<<PB5);