Make fast PWM optional.

In some cases the heater switching MOSFETs overheat and using a lower
PWM frequency is advised. See also:
http://reprap.org/wiki/Gen7_Research#Heat_vs._PWM_Frequency

config.default.h

@@ -440,6 +440,13 @@ PWM value for 'off'
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+#define	FAST_PWM
+
 /// this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

config.gen3.h

@@ -447,6 +447,13 @@ DEFINE_TEMP_SENSOR(bed,			TT_INTERCOM,	1,		0)
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+#define	FAST_PWM
+
 /// this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

config.gen6.h

@@ -428,12 +428,19 @@ PWM value for 'off'
 */
 #define		STEP_INTERRUPT_INTERRUPTIBLE	1
 
-/*
+/**
 	temperature history count. This is how many temperature readings to keep in order to calculate derivative in PID loop
 	higher values make PID derivative term more stable at the expense of reaction time
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+#define	FAST_PWM
+
 // this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

config.gen7.h

@@ -446,6 +446,13 @@ PWM value for 'off'
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+// #define	FAST_PWM
+
 /// this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

config.ramps-v1.2.h

@@ -440,6 +440,13 @@ PWM value for 'off'
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+#define	FAST_PWM
+
 /// this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

config.ramps-v1.3.h

@@ -445,6 +445,13 @@ PWM value for 'off'
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+#define	FAST_PWM
+
 /// this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

config.sanguinololu-v1.1.h

@@ -444,6 +444,13 @@ PWM value for 'off'
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+#define	FAST_PWM
+
 /// this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

config.sanguinololu-v1.2.h

@@ -444,6 +444,13 @@ PWM value for 'off'
 */
 #define	TH_COUNT					8
 
+/** \def FAST_PWM
+	Teacup offers two PWM frequencies, 76(61) Hz and 78000(62500) Hz on a 20(16) MHz electronics. The faster one is the default, as it's what most other firmwares do. It can make the heater MOSFETs pretty hot, though.
+
+	Comment this option out if your MOSFETs overheat. Drawback is, in a quiet environment you might notice the heaters and your power supply humming, then.
+*/
+#define	FAST_PWM
+
 /// this is the scaling of internally stored PID values. 1024L is a good value
 #define	PID_SCALE						1024L
 

mendel.c

@@ -186,13 +186,29 @@ void io_init(void) {
 
 	// setup PWM timers: fast PWM, no prescaler
 	TCCR0A = MASK(WGM01) | MASK(WGM00);
-	TCCR0B = MASK(CS00);
+	// PWM frequencies in TCCR0B, see page 108 of the ATmega644 reference.
+	TCCR0B = MASK(CS00); // F_CPU / 256 (about 78(62.5) kHz on a 20(16) MHz chip)
+	//TCCR0B = MASK(CS01);              // F_CPU / 256 / 8  (about 9.8(7.8) kHz)
+	//TCCR0B = MASK(CS00) | MASK(CS01); // F_CPU / 256 / 64  (about 1220(977) Hz)
+	//TCCR0B = MASK(CS02);              // F_CPU / 256 / 256  (about 305(244) Hz)
+	#ifndef FAST_PWM
+		TCCR0B = MASK(CS00) | MASK(CS02); // F_CPU / 256 / 1024  (about 76(61) Hz)
+	#endif
 	TIMSK0 = 0;
 	OCR0A = 0;
 	OCR0B = 0;
 
 	TCCR2A = MASK(WGM21) | MASK(WGM20);
-	TCCR2B = MASK(CS20);
+	// PWM frequencies in TCCR2B, see page 156 of the ATmega644 reference.
+	TCCR2B = MASK(CS20); // F_CPU / 256  (about 78(62.5) kHz on a 20(16) MHz chip)
+	//TCCR2B = MASK(CS21);              // F_CPU / 256 / 8  (about 9.8(7.8) kHz)
+	//TCCR2B = MASK(CS20) | MASK(CS21); // F_CPU / 256 / 32  (about 2.4(2.0) kHz)
+	//TCCR2B = MASK(CS22);              // F_CPU / 256 / 64  (about 1220(977) Hz)
+	//TCCR2B = MASK(CS20) | MASK(CS22); // F_CPU / 256 / 128  (about 610(488) Hz)
+	//TCCR2B = MASK(CS21) | MASK(CS22); // F_CPU / 256 / 256  (about 305(244) Hz)
+	#ifndef FAST_PWM
+		TCCR2B = MASK(CS20) | MASK(CS21) | MASK(CS22); // F_CPU / 256 / 1024
+	#endif
 	TIMSK2 = 0;
 	OCR2A = 0;
 	OCR2B = 0;