diff --git a/Marlin/Configuration.h b/Marlin/Configuration.h
index b5821438597e487516a430357b1642cca19efc11..3facece4b7701e1166357979fc2153c5279bdf21 100644
--- a/Marlin/Configuration.h
+++ b/Marlin/Configuration.h
@@ -1425,6 +1425,12 @@
// at zero value, there are 128 effective control positions.
#define SOFT_PWM_SCALE 0
+// If SOFT_PWM_SCALE is set to a value higher than 0, dithering can
+// be used to mitigate the associated resolution loss. If enabled,
+// some of the PWM cycles are stretched so on average the wanted
+// duty cycle is attained.
+//#define SOFT_PWM_DITHER
+
// Temperature status LEDs that display the hotend and bed temperature.
// If all hotends and bed temperature and temperature setpoint are < 54C then the BLUE led is on.
// Otherwise the RED led is on. There is 1C hysteresis.
diff --git a/Marlin/temperature.cpp b/Marlin/temperature.cpp
index 883133806ee340c10f18443fb96b5e28926d1c8f..50a8f7b1d20beead2c381c570982e8f44defaf38 100644
--- a/Marlin/temperature.cpp
+++ b/Marlin/temperature.cpp
@@ -1512,6 +1512,8 @@ void Temperature::isr() {
static uint8_t temp_count = 0;
static TempState temp_state = StartupDelay;
static uint8_t pwm_count = _BV(SOFT_PWM_SCALE);
+ // avoid multiple loads of pwm_count
+ uint8_t pwm_count_tmp = pwm_count;
// Static members for each heater
#if ENABLED(SLOW_PWM_HEATERS)
@@ -1521,7 +1523,7 @@ void Temperature::isr() {
static uint8_t state_heater_ ## n = 0; \
static uint8_t state_timer_heater_ ## n = 0
#else
- #define ISR_STATICS(n) static uint8_t soft_pwm_ ## n
+ #define ISR_STATICS(n) static uint8_t soft_pwm_ ## n = 0
#endif
// Statics per heater
@@ -1544,72 +1546,82 @@ void Temperature::isr() {
#endif
#if DISABLED(SLOW_PWM_HEATERS)
+ constexpr uint8_t pwm_mask =
+ #if ENABLED(SOFT_PWM_DITHER)
+ _BV(SOFT_PWM_SCALE) - 1
+ #else
+ 0
+ #endif
+ ;
+
/**
* Standard PWM modulation
*/
- if (pwm_count == 0) {
- soft_pwm_0 = soft_pwm[0];
- WRITE_HEATER_0(soft_pwm_0 > 0 ? HIGH : LOW);
+ if (pwm_count_tmp >= 127) {
+ pwm_count_tmp -= 127;
+ soft_pwm_0 = (soft_pwm_0 & pwm_mask) + soft_pwm[0];
+ WRITE_HEATER_0(soft_pwm_0 > pwm_mask ? HIGH : LOW);
#if HOTENDS > 1
- soft_pwm_1 = soft_pwm[1];
- WRITE_HEATER_1(soft_pwm_1 > 0 ? HIGH : LOW);
+ soft_pwm_1 = (soft_pwm_1 & pwm_mask) + soft_pwm[1];
+ WRITE_HEATER_1(soft_pwm_1 > pwm_mask ? HIGH : LOW);
#if HOTENDS > 2
- soft_pwm_2 = soft_pwm[2];
- WRITE_HEATER_2(soft_pwm_2 > 0 ? HIGH : LOW);
+ soft_pwm_2 = (soft_pwm_2 & pwm_mask) + soft_pwm[2];
+ WRITE_HEATER_2(soft_pwm_2 > pwm_mask ? HIGH : LOW);
#if HOTENDS > 3
- soft_pwm_3 = soft_pwm[3];
- WRITE_HEATER_3(soft_pwm_3 > 0 ? HIGH : LOW);
+ soft_pwm_3 = (soft_pwm_3 & pwm_mask) + soft_pwm[3];
+ WRITE_HEATER_3(soft_pwm_3 > pwm_mask ? HIGH : LOW);
#endif
#endif
#endif
#if HAS_HEATER_BED
- soft_pwm_BED = soft_pwm_bed;
- WRITE_HEATER_BED(soft_pwm_BED > 0 ? HIGH : LOW);
+ soft_pwm_BED = (soft_pwm_BED & pwm_mask) + soft_pwm_bed;
+ WRITE_HEATER_BED(soft_pwm_BED > pwm_mask ? HIGH : LOW);
#endif
#if ENABLED(FAN_SOFT_PWM)
#if HAS_FAN0
- soft_pwm_fan[0] = fanSpeedSoftPwm[0] >> 1;
- WRITE_FAN(soft_pwm_fan[0] > 0 ? HIGH : LOW);
+ soft_pwm_fan[0] = (soft_pwm_fan[0] & pwm_mask) + fanSpeedSoftPwm[0] >> 1;
+ WRITE_FAN(soft_pwm_fan[0] > pwm_mask ? HIGH : LOW);
#endif
#if HAS_FAN1
- soft_pwm_fan[1] = fanSpeedSoftPwm[1] >> 1;
- WRITE_FAN1(soft_pwm_fan[1] > 0 ? HIGH : LOW);
+ soft_pwm_fan[1] = (soft_pwm_fan[1] & pwm_mask) + fanSpeedSoftPwm[1] >> 1;
+ WRITE_FAN1(soft_pwm_fan[1] > pwm_mask ? HIGH : LOW);
#endif
#if HAS_FAN2
- soft_pwm_fan[2] = fanSpeedSoftPwm[2] >> 1;
- WRITE_FAN2(soft_pwm_fan[2] > 0 ? HIGH : LOW);
+ soft_pwm_fan[2] = (soft_pwm_fan[2] & pwm_mask) + fanSpeedSoftPwm[2] >> 1;
+ WRITE_FAN2(soft_pwm_fan[2] > pwm_mask ? HIGH : LOW);
#endif
#endif
}
-
- if (soft_pwm_0 < pwm_count) WRITE_HEATER_0(0);
- #if HOTENDS > 1
- if (soft_pwm_1 < pwm_count) WRITE_HEATER_1(0);
+ else {
+ if (soft_pwm_0 <= pwm_count_tmp) WRITE_HEATER_0(0);
+ #if HOTENDS > 1
+ if (soft_pwm_1 <= pwm_count_tmp) WRITE_HEATER_1(0);
+ #endif
#if HOTENDS > 2
- if (soft_pwm_2 < pwm_count) WRITE_HEATER_2(0);
- #if HOTENDS > 3
- if (soft_pwm_3 < pwm_count) WRITE_HEATER_3(0);
- #endif
+ if (soft_pwm_2 <= pwm_count_tmp) WRITE_HEATER_2(0);
#endif
- #endif
-
- #if HAS_HEATER_BED
- if (soft_pwm_BED < pwm_count) WRITE_HEATER_BED(0);
- #endif
-
- #if ENABLED(FAN_SOFT_PWM)
- #if HAS_FAN0
- if (soft_pwm_fan[0] < pwm_count) WRITE_FAN(0);
+ #if HOTENDS > 3
+ if (soft_pwm_3 <= pwm_count_tmp) WRITE_HEATER_3(0);
#endif
- #if HAS_FAN1
- if (soft_pwm_fan[1] < pwm_count) WRITE_FAN1(0);
+
+ #if HAS_HEATER_BED
+ if (soft_pwm_BED <= pwm_count_tmp) WRITE_HEATER_BED(0);
#endif
- #if HAS_FAN2
- if (soft_pwm_fan[2] < pwm_count) WRITE_FAN2(0);
+
+ #if ENABLED(FAN_SOFT_PWM)
+ #if HAS_FAN0
+ if (soft_pwm_fan[0] <= pwm_count_tmp) WRITE_FAN(0);
+ #endif
+ #if HAS_FAN1
+ if (soft_pwm_fan[1] <= pwm_count_tmp) WRITE_FAN1(0);
+ #endif
+ #if HAS_FAN2
+ if (soft_pwm_fan[2] <= pwm_count_tmp) WRITE_FAN2(0);
+ #endif
#endif
- #endif
+ }
// SOFT_PWM_SCALE to frequency:
//
@@ -1619,8 +1631,7 @@ void Temperature::isr() {
// 3: / 16 = 61.0352 Hz
// 4: / 8 = 122.0703 Hz
// 5: / 4 = 244.1406 Hz
- pwm_count += _BV(SOFT_PWM_SCALE);
- pwm_count &= 0x7F;
+ pwm_count = pwm_count_tmp + _BV(SOFT_PWM_SCALE);
#else // SLOW_PWM_HEATERS
@@ -1694,7 +1705,8 @@ void Temperature::isr() {
#endif
#if ENABLED(FAN_SOFT_PWM)
- if (pwm_count == 0) {
+ if (pwm_count_tmp >= 127) {
+ pwm_count_tmp = 0;
#if HAS_FAN0
soft_pwm_fan[0] = fanSpeedSoftPwm[0] >> 1;
WRITE_FAN(soft_pwm_fan[0] > 0 ? HIGH : LOW);
@@ -1709,15 +1721,15 @@ void Temperature::isr() {
#endif
}
#if HAS_FAN0
- if (soft_pwm_fan[0] < pwm_count) WRITE_FAN(0);
+ if (soft_pwm_fan[0] <= pwm_count_tmp) WRITE_FAN(0);
#endif
#if HAS_FAN1
- if (soft_pwm_fan[1] < pwm_count) WRITE_FAN1(0);
+ if (soft_pwm_fan[1] <= pwm_count_tmp) WRITE_FAN1(0);
#endif
#if HAS_FAN2
- if (soft_pwm_fan[2] < pwm_count) WRITE_FAN2(0);
+ if (soft_pwm_fan[2] <= pwm_count_tmp) WRITE_FAN2(0);
#endif
- #endif //FAN_SOFT_PWM
+ #endif // FAN_SOFT_PWM
// SOFT_PWM_SCALE to frequency:
//
@@ -1727,13 +1739,13 @@ void Temperature::isr() {
// 3: / 16 = 61.0352 Hz
// 4: / 8 = 122.0703 Hz
// 5: / 4 = 244.1406 Hz
- pwm_count += _BV(SOFT_PWM_SCALE);
- pwm_count &= 0x7F;
+ pwm_count = pwm_count_tmp + _BV(SOFT_PWM_SCALE);
- // increment slow_pwm_count only every 64 pwm_count (e.g., every 8s)
- if ((pwm_count % 64) == 0) {
+ // increment slow_pwm_count only every 64th pwm_count,
+ // i.e. yielding a PWM frequency of 16/128 Hz (8s).
+ if (((pwm_count >> SOFT_PWM_SCALE) & 0x3F) == 0) {
slow_pwm_count++;
- slow_pwm_count &= 0x7f;
+ slow_pwm_count &= 0x7F;
// EXTRUDER 0
if (state_timer_heater_0 > 0) state_timer_heater_0--;
@@ -1749,7 +1761,7 @@ void Temperature::isr() {
#if HAS_HEATER_BED
if (state_timer_heater_BED > 0) state_timer_heater_BED--;
#endif
- } // (pwm_count % 64) == 0
+ } // ((pwm_count >> SOFT_PWM_SCALE) & 0x3F) == 0
#endif // SLOW_PWM_HEATERS