added PWM dithering support

Author: tridge

Inc/eeprom.h

@@ -47,7 +47,8 @@ typedef union EEprom_u {
         uint8_t sine_mode_power; // 45
         uint8_t input_type; // 46
         uint8_t auto_advance; // 47
-        uint8_t reserved_2[4]; //48-51
+        uint8_t pwm_dithering; // 48
+        uint8_t reserved_2[3]; //49-51
         uint8_t tune[124]; // 52-175
         struct {
             uint8_t can_node; // 176

Src/DroneCAN/DroneCAN.c

@@ -152,6 +152,7 @@ static const struct parameter {
         { "BEEP_VOLUME",            T_UINT8, 0, 11,  5, &eepromBuffer.beep_volume},
         { "VARIABLE_PWM",           T_BOOL,  0, 1,   1, &eepromBuffer.variable_pwm},
         { "PWM_FREQUENCY",          T_UINT8, 8, 48,  24, &eepromBuffer.pwm_frequency},
+        { "PWM_DITHERING",          T_UINT8, 0, 200, 0, &eepromBuffer.pwm_dithering},
         { "USE_SIN_START",          T_BOOL,  0, 1,   0, &eepromBuffer.use_sine_start},
         { "COMP_PWM",               T_BOOL,  0, 1,   1, &eepromBuffer.comp_pwm},
         { "STUCK_ROTOR_PROTECTION", T_BOOL,  0, 1,   1, &eepromBuffer.stuck_rotor_protection},

Src/main.c

@@ -750,6 +750,9 @@ void loadEEpromSettings()
 //    if (!eepromBuffer.comp_pwm) {
 //        eepromBuffer.bi_direction = 0;
 //    }
+    if (eepromBuffer.pwm_dithering > 128) {
+        eepromBuffer.pwm_dithering = 0;
+    }
 }
 
 void saveEEpromSettings()
@@ -1240,6 +1243,18 @@ if (!stepper_sine && armed) {
 #endif
 }
 
+/*
+  calculate a PWM dithering value
+ */
+static uint16_t pwmDither(uint16_t reload, uint16_t dithering)
+{
+    // simple LCG random number generator
+    static uint8_t seed;
+    seed = (((uint32_t)seed) * 1103515245U + 12345U);
+    int16_t r = (seed % (dithering * 2)) - dithering;
+    return reload + r;
+}
+
 void tenKhzRoutine()
 { // 20khz as of 2.00 to be renamed
     duty_cycle = duty_cycle_setpoint;
@@ -1408,10 +1423,19 @@ void tenKhzRoutine()
                 fast_accel = 0;
             }
         }
+
+        /*
+          possibly add PWM dithering to reduce impact of harmonics
+         */
+        uint16_t tim1_arr_used = tim1_arr;
+        if (eepromBuffer.pwm_dithering > 0) {
+            tim1_arr_used = pwmDither(tim1_arr, eepromBuffer.pwm_dithering);
+        }
+
         if ((armed && running) && input > 47) {
             if (eepromBuffer.variable_pwm) {
             }
-            adjusted_duty_cycle = ((duty_cycle * tim1_arr) / 2000) + 1;
+            adjusted_duty_cycle = ((duty_cycle * tim1_arr_used) / 2000) + 1;
 
         } else {
 
@@ -1422,7 +1446,7 @@ void tenKhzRoutine()
             }
         }
         last_duty_cycle = duty_cycle;
-        SET_AUTO_RELOAD_PWM(tim1_arr);
+        SET_AUTO_RELOAD_PWM(tim1_arr_used);
         SET_DUTY_CYCLE_ALL(adjusted_duty_cycle);
     }
 #endif // ndef brushed_mode