From fa0c389e56f76a631a4616bf36b85ff7ee875c04 Mon Sep 17 00:00:00 2001
From: Christian Pointner <equinox@spreadspace.org>
Date: Sun, 12 Sep 2021 23:38:19 +0200
Subject: add fan tacho

---
 table-fan/Makefile    |  1 +
 table-fan/table-fan.c | 36 ++++++++++++++++++++++++++++++++----
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/table-fan/Makefile b/table-fan/Makefile
index c41073f..85f972c 100644
--- a/table-fan/Makefile
+++ b/table-fan/Makefile
@@ -26,6 +26,7 @@ OBJ := $(NAME).o
 LIBS := util led lufa-descriptor-usbserial usbio
 EXTERNAL_LIBS := lufa
 SPREADAVR_PATH := ../contrib/avr-utils
+PRINTF_HAS_FLOAT := 1
 RESET_FUNC := $(SPREADAVR_PATH)/tools/reset_lufa_cdc
 RESET_PARAM := 'r'
 
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);
-- 
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