From cb334238cc872cbcf634c91441b8ac0a180540af Mon Sep 17 00:00:00 2001
From: Robert Pelnar <robert.pelnar@seznam.cz>
Date: Thu, 6 Dec 2018 15:18:07 +0100
Subject: [PATCH] Slow PWM fan @ 62.5Hz

---
 Firmware/Configuration.h |  3 ++-
 Firmware/temperature.cpp | 19 +++++++++++--------
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/Firmware/Configuration.h b/Firmware/Configuration.h
index 3bed653b7..0ca8f601d 100644
--- a/Firmware/Configuration.h
+++ b/Firmware/Configuration.h
@@ -477,7 +477,8 @@ your extruder heater takes 2 minutes to hit the target on heating.
 // Use software PWM to drive the fan, as for the heaters. This uses a very low frequency
 // which is not ass annoying as with the hardware PWM. On the other hand, if this frequency
 // is too low, you should also increment SOFT_PWM_SCALE.
-//#define FAN_SOFT_PWM
+#define FAN_SOFT_PWM
+#define FAN_SOFT_PWM_BITS 4 //PWM bit resolution = 4bits, freq = 62.5Hz
 
 // Incrementing this by 1 will double the software PWM frequency,
 // affecting heaters, and the fan if FAN_SOFT_PWM is enabled.
diff --git a/Firmware/temperature.cpp b/Firmware/temperature.cpp
index cae3fada7..98e8aee37 100644
--- a/Firmware/temperature.cpp
+++ b/Firmware/temperature.cpp
@@ -1024,7 +1024,7 @@ void tp_init()
     setPwmFrequency(FAN_PIN, 1); // No prescaling. Pwm frequency = F_CPU/256/8
     #endif
     #ifdef FAN_SOFT_PWM
-    soft_pwm_fan = fanSpeedSoftPwm / 2;
+    soft_pwm_fan = fanSpeedSoftPwm / (1 << (8 - FAN_SOFT_PWM_BITS));
     #endif
   #endif
 
@@ -1599,12 +1599,15 @@ ISR(TIMER0_COMPB_vect)
 #if defined(HEATER_BED_PIN) && HEATER_BED_PIN > -1
     soft_pwm_b = soft_pwm_bed;
     if(soft_pwm_b > 0) WRITE(HEATER_BED_PIN,1); else WRITE(HEATER_BED_PIN,0);
-#endif
-#ifdef FAN_SOFT_PWM
-    soft_pwm_fan = fanSpeedSoftPwm / 2;
-    if(soft_pwm_fan > 0) WRITE(FAN_PIN,1); else WRITE(FAN_PIN,0);
 #endif
   }
+#ifdef FAN_SOFT_PWM
+  if ((pwm_count & ((1 << FAN_SOFT_PWM_BITS) - 1)) == 0)
+  {
+    soft_pwm_fan = fanSpeedSoftPwm / (1 << (8 - FAN_SOFT_PWM_BITS));
+    if(soft_pwm_fan > 0) WRITE(FAN_PIN,1); else WRITE(FAN_PIN,0);
+  }
+#endif
   if(soft_pwm_0 < pwm_count)
   { 
     WRITE(HEATER_0_PIN,0);
@@ -1623,7 +1626,7 @@ ISR(TIMER0_COMPB_vect)
   if(soft_pwm_b < pwm_count) WRITE(HEATER_BED_PIN,0);
 #endif
 #ifdef FAN_SOFT_PWM
-  if(soft_pwm_fan < pwm_count) WRITE(FAN_PIN,0);
+  if (soft_pwm_fan < (pwm_count & ((1 << FAN_SOFT_PWM_BITS) - 1))) WRITE(FAN_PIN,0);
 #endif
   
   pwm_count += (1 << SOFT_PWM_SCALE);
@@ -1810,8 +1813,8 @@ ISR(TIMER0_COMPB_vect)
 #endif
   
 #ifdef FAN_SOFT_PWM
-  if (pwm_count == 0){
-    soft_pwm_fan = fanSpeedSoftPwm / 2;
+  if ((pwm_count & ((1 << FAN_SOFT_PWM_BITS) - 1)) == 0)
+    soft_pwm_fan = fanSpeedSoftPwm / (1 << (8 - FAN_SOFT_PWM_BITS));
     if (soft_pwm_fan > 0) WRITE(FAN_PIN,1); else WRITE(FAN_PIN,0);
   }
   if (soft_pwm_fan < pwm_count) WRITE(FAN_PIN,0);