From 7e4f02dd4e72e97b8f5335876142b5bd6179cee1 Mon Sep 17 00:00:00 2001
From: Christian Pointner <equinox@spreadspace.org>
Date: Mon, 13 Sep 2021 19:58:57 +0200
Subject: add average for fan tacho

---
 table-fan/fan.c       | 45 +++++++++++++++++++++++++++++----------------
 table-fan/fan.h       |  2 ++
 table-fan/table-fan.c |  2 +-
 3 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/table-fan/fan.c b/table-fan/fan.c
index daa33f4..a843924 100644
--- a/table-fan/fan.c
+++ b/table-fan/fan.c
@@ -54,6 +54,35 @@ void fan_init(void)
   TCCR4B = (1<<CS41); // start timer
 }
 
+#define TACHO_DATA_LEN 8
+static uint16_t tacho_data[TACHO_DATA_LEN];
+static uint8_t tacho_data_idx = 0;
+static uint16_t tacho_last_ts = 0;
+
+ISR(TIMER1_CAPT_vect)
+{
+  uint16_t current = ICR1;
+  if(current > tacho_last_ts) {
+    tacho_data[tacho_data_idx] = current - tacho_last_ts;
+  } else {
+    tacho_data[tacho_data_idx] = (UINT16_MAX - tacho_last_ts) + current;
+  }
+  tacho_last_ts = current;
+  tacho_data_idx = (tacho_data_idx >= (TACHO_DATA_LEN-1)) ? 0 : tacho_data_idx+1;
+}
+
+uint16_t fan_get_rpm(void)
+{
+  uint32_t sum = 0;
+  cli();
+  for(uint8_t i = 0; i < TACHO_DATA_LEN; i++) {
+    sum += tacho_data[i];
+  }
+  sei();
+
+  return (1875000 / (sum / TACHO_DATA_LEN));
+}
+
 void fan_speed_set(uint8_t val)
 {
   OCR4B = (val > PWM_VAL_MAX) ? PWM_VAL_MAX : val;
@@ -75,19 +104,3 @@ void fan_speed_dec(void)
   if(OCR4B > 0)
     OCR4B--;
 }
-
-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;
-
-  uint16_t rpm = 1875000 / diff;
-  printf("\rspeed: %6d rpm", rpm);
-}
diff --git a/table-fan/fan.h b/table-fan/fan.h
index 125d7aa..111c947 100644
--- a/table-fan/fan.h
+++ b/table-fan/fan.h
@@ -25,6 +25,8 @@
 
 void fan_init(void);
 
+uint16_t fan_get_rpm(void);
+
 void fan_speed_set(uint8_t val);
 uint8_t fan_speed_get(void);
 void fan_speed_inc(void);
diff --git a/table-fan/table-fan.c b/table-fan/table-fan.c
index e3c3842..1f0cf4f 100644
--- a/table-fan/table-fan.c
+++ b/table-fan/table-fan.c
@@ -38,8 +38,8 @@ void handle_cmd(uint8_t cmd)
   case '+': fan_speed_inc();/* printf("pwm = %d\r\n", fan_speed_get()); */ break;
   case '-': fan_speed_dec();/* printf("pwm = %d\r\n", fan_speed_get()); */ break;
   case 'r': reset2bootloader(); break;
-  default: return; // printf("error\r\n"); return;
   }
+  printf("\rspeed: %5d rpm", fan_get_rpm());
 }
 
 int main(void)
-- 
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