Allows user to set (almost) any PWM frequency

Marlin/Configuration_adv.h

@@ -241,6 +241,33 @@
 //#define FAN_MIN_PWM 50
 //#define FAN_MAX_PWM 128
 
+/**
+ * FAST PWM FAN Settings
+ *
+ * Use to change the FAST FAN PWM frequency (if enabled in Configuration.h)
+ * Combinations of PWM Modes, prescale values and TOP resolutions are used internally to produce a
+ * frequency as close as possible to the desired frequency.
+ *
+ * FAST_PWM_FAN_FREQUENCY [undefined by default]
+ *   Set this to your desired frequency.
+ *   If left undefined this defaults to F = F_CPU/(2*255*1)
+ *   ie F = 31.4 Khz on 16 MHz microcontrollers or F = 39.2 KHz on 20 MHz microcontrollers
+ *   These defaults are the same as with the old FAST_PWM_FAN implementation - no migration is required
+ *   NOTE: Setting very low frequencies (< 10 Hz) may result in unexpected timer behaviour.
+ *
+ * USE_OCR2A_AS_TOP [undefined by default]
+ *   Boards that use TIMER2 for PWM have limitations resulting in only a few possible frequencies on TIMER2:
+ *   16MHz MCUs: [62.5KHz, 31.4KHz (default), 7.8KHz, 3.92KHz, 1.95KHz, 977Hz, 488Hz, 244Hz, 60Hz, 122Hz, 30Hz]
+ *   20MHz MCUs: [78.1KHz, 39.2KHz (default), 9.77KHz, 4.9KHz, 2.44KHz, 1.22KHz, 610Hz, 305Hz, 153Hz, 76Hz, 38Hz]
+ *   A greater range can be achieved by enabling USE_OCR2A_AS_TOP. But note that this option blocks the use of
+ *   PWM on pin OC2A. Only use this option if you don't need PWM on 0C2A. (Check your schematic.)
+ *   USE_OCR2A_AS_TOP sacrifices duty cycle control resolution to achieve this broader range of frequencies.
+ */
+#if ENABLED(FAST_PWM_FAN)
+  //#define FAST_PWM_FAN_FREQUENCY 31400
+  //#define USE_OCR2A_AS_TOP
+#endif
+
 // @section extruder
 
 /**

Marlin/src/HAL/HAL_AVR/SanityCheck.h

@@ -35,6 +35,13 @@
   #endif
 #endif
 
+/**
+ * Checks for FAST PWM
+ */
+#if ENABLED(FAST_PWM_FAN) && (ENABLED(USE_OCR2A_AS_TOP) && defined(TCCR2))
+    #error "USE_OCR2A_AS_TOP does not apply to devices with a single output TIMER2"
+#endif
+
 /**
  * Sanity checks for Spindle / Laser
  */

Marlin/src/HAL/HAL_AVR/fastio_AVR.h

@@ -132,6 +132,18 @@ enum WaveGenMode : char {
   WGM_FAST_PWM_OCRnA   // 15  COM OCnA
 };
 
+// Wavefore Generation Modes (Timer 2 only)
+enum WaveGenMode2 : char {
+  WGM2_NORMAL,          // 0
+  WGM2_PWM_PC,          // 1
+  WGM2_CTC_OCR2A,       // 2
+  WGM2_FAST_PWM,        // 3
+  WGM2_reserved_1,      // 4
+  WGM2_PWM_PC_OCR2A,    // 5
+  WGM2_reserved_2,      // 6
+  WGM2_FAST_PWM_OCR2A,  // 7
+};
+
 // Compare Modes
 enum CompareMode : char {
   COM_NORMAL,          //  0
@@ -186,6 +198,11 @@ enum ClockSource2 : char {
     TCCR##T##B = (TCCR##T##B & ~(0x3 << WGM##T##2)) | (((int(V) >> 2) & 0x3) << WGM##T##2); \
   }while(0)
 #define SET_WGM(T,V) _SET_WGM(T,WGM_##V)
+// Runtime (see Temperature::set_pwm_frequency):
+#define _SET_WGMnQ(TCCRnQ, V) do{ \
+    *(TCCRnQ)[0] = (*(TCCRnQ)[0] & ~(0x3 << 0)) | (( int(V)       & 0x3) << 0); \
+    *(TCCRnQ)[1] = (*(TCCRnQ)[1] & ~(0x3 << 3)) | (((int(V) >> 2) & 0x3) << 3); \
+  }while(0)
 
 // Set Clock Select bits
 // Ex: SET_CS3(PRESCALER_64);
@@ -211,6 +228,10 @@ enum ClockSource2 : char {
 #define SET_CS4(V) _SET_CS4(CS_##V)
 #define SET_CS5(V) _SET_CS5(CS_##V)
 #define SET_CS(T,V) SET_CS##T(V)
+// Runtime (see Temperature::set_pwm_frequency)
+#define _SET_CSn(TCCRnQ, V) do{ \
+    (*(TCCRnQ)[1] = (*(TCCRnQ[1]) & ~(0x7 << 0)) | ((int(V) & 0x7) << 0)); \
+  }while(0)
 
 // Set Compare Mode bits
 // Ex: SET_COMS(4,CLEAR_SET,CLEAR_SET,CLEAR_SET);
@@ -220,6 +241,22 @@ enum ClockSource2 : char {
 #define SET_COMB(T,V) SET_COM(T,B,V)
 #define SET_COMC(T,V) SET_COM(T,C,V)
 #define SET_COMS(T,V1,V2,V3) do{ SET_COMA(T,V1); SET_COMB(T,V2); SET_COMC(T,V3); }while(0)
+// Runtime (see Temperature::set_pwm_duty)
+#define _SET_COMnQ(TCCRnQ, Q, V) do{ \
+    (*(TCCRnQ)[0] = (*(TCCRnQ)[0] & ~(0x3 << (6-2*(Q)))) | (int(V) << (6-2*(Q)))); \
+  }while(0)
+
+// Set OCRnQ register
+// Runtime (see Temperature::set_pwm_duty):
+#define _SET_OCRnQ(OCRnQ, Q, V) do{ \
+    (*(OCRnQ)[(Q)] = (0x0000) | (int(V) & 0xFFFF)); \
+  }while(0)
+
+// Set ICRn register (one per timer)
+// Runtime (see Temperature::set_pwm_frequency)
+#define _SET_ICRn(ICRn, V) do{ \
+    (*(ICRn) = (0x0000) | (int(V) & 0xFFFF)); \
+  }while(0)
 
 // Set Noise Canceler bit
 // Ex: SET_ICNC(2,1)

Marlin/src/inc/Conditionals_post.h

@@ -1213,6 +1213,13 @@
   #error "FAN_MIN_PWM must be less than or equal to FAN_MAX_PWM."
 #endif
 
+/**
+ * FAST PWM FAN Settings
+ */
+#if ENABLED(FAST_PWM_FAN) && !defined(FAST_PWM_FAN_FREQUENCY)
+  #define FAST_PWM_FAN_FREQUENCY ((F_CPU) / (2 * 255 * 1)) // Fan frequency default
+#endif
+
 /**
  * Bed Probe dependencies
  */

Marlin/src/module/planner.cpp

@@ -1273,6 +1273,18 @@ void Planner::check_axes_activity() {
       #if HAS_FAN2
         thermalManager.soft_pwm_amount_fan[2] = CALC_FAN_SPEED(2);
       #endif
+
+    #elif ENABLED(FAST_PWM_FAN)
+      #if HAS_FAN0
+        thermalManager.set_pwm_duty(FAN_PIN, CALC_FAN_SPEED(0));
+      #endif
+      #if HAS_FAN1
+        thermalManager.set_pwm_duty(FAN1_PIN, CALC_FAN_SPEED(1));
+      #endif
+      #if HAS_FAN2
+        thermalManager.set_pwm_duty(FAN2_PIN, CALC_FAN_SPEED(2));
+      #endif
+
     #else
       #if HAS_FAN0
         analogWrite(FAN_PIN, CALC_FAN_SPEED(0));