pwm improvements

-add capability to change pwm signal frequency with analogWriteFrequency
-improve pwm signal frequency accuracy

Author: bigdinotech

cores/arduino/Arduino.h

@@ -95,6 +95,8 @@ typedef struct _PinDescription
 /* Pins table to be instanciated into variant.cpp */
 extern PinDescription g_APinDescription[] ;
 
+extern uint32_t pwmPeriod[4];
+
 #ifdef __cplusplus
 } // extern "C"
 

cores/arduino/wiring_analog.c

@@ -27,11 +27,12 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 /* Standard Arduino PWM resolution */
 static int _writeResolution = 8;
 static int _readResolution = 10;
-
+uint32_t maxResolutionValue = 0xFF;
 
 void analogWriteResolution(int res)
 {
     _writeResolution = res;
+    maxResolutionValue = 0xFFFFFFFF >> (32-res);
 }
 
 void analogReadResolution(int res)
@@ -49,7 +50,7 @@ static inline uint32_t mapResolution(uint32_t value, uint32_t from, uint32_t to)
          return value << (to-from);
 }
 
-void analogWrite(uint8_t pin, int val)
+void analogWrite(uint8_t pin, uint32_t val)
 {
     if (! digitalPinHasPWM(pin))
     {
@@ -75,20 +76,12 @@ void analogWrite(uint8_t pin, int val)
     } else {
         /* PWM for everything in between */
         PinDescription *p = &g_APinDescription[pin];
-        uint32_t hcnt = mapResolution(val, _writeResolution, PWM_RESOLUTION);
-        uint32_t lcnt = PWM_MAX_DUTY_CYCLE - hcnt;
-        uint32_t offset;
-
-        /* For Arduino Uno compatibilty, we scale up frequency on certain pins */
-        hcnt >>= p->ulPwmScale;
-        lcnt >>= p->ulPwmScale;
-
-        /* Each count must be > 0 */
-        if (hcnt < PWM_MIN_DUTY_CYCLE)
-            hcnt = PWM_MIN_DUTY_CYCLE;
-        if (lcnt < PWM_MIN_DUTY_CYCLE)
-            lcnt = PWM_MIN_DUTY_CYCLE;
 
+        uint32_t offset;
+        
+        uint32_t hcnt = (val/(float)maxResolutionValue) * pwmPeriod[p->ulPwmChan];
+        uint32_t lcnt = pwmPeriod[p->ulPwmChan] - hcnt;
+        
         /* Set the high count period (duty cycle) */
         offset = ((p->ulPwmChan * QRK_PWM_N_LCNT2_LEN) + QRK_PWM_N_LOAD_COUNT2);
         MMIO_REG_VAL(QRK_PWM_BASE_ADDR + offset) = hcnt;
@@ -139,6 +132,13 @@ uint32_t analogRead(uint32_t pin)
 
 }
 
+void analogWriteFrequency(uint8_t pin, uint32_t freq)
+{
+    //convert frequency to period in clock ticks
+    PinDescription *p = &g_APinDescription[pin];
+    pwmPeriod[p->ulPwmChan] = F_CPU / freq;
+}
+
 #ifdef __cplusplus
 }
 #endif

cores/arduino/wiring_analog.h

@@ -33,6 +33,8 @@ typedef enum _eAnalogReference
   AR_DEFAULT,
 } eAnalogReference ;
 
+#define PWM_PERIOD 	65306	//490 Hz
+
 /*
  * \brief Configures the reference voltage used for analog input (i.e. the value used as the top of the input range).
  * This function is kept only for compatibility with existing AVR based API.
@@ -47,7 +49,7 @@ extern void analogReference( eAnalogReference ulMode ) ;
  * \param pin
  * \param val
  */
-extern void analogWrite( uint8_t pin, int val ) ;
+extern void analogWrite( uint8_t pin, uint32_t val ) ;
 
 /*
  * \brief Reads the value from the specified analog pin.
@@ -72,6 +74,13 @@ extern void analogReadResolution(int res);
  */
 extern void analogWriteResolution(int res);
 
+/*
+ * \brief Set the frequency of analogWrite parameters.
+ *
+ * \param res
+ */
+extern void analogWriteFrequency(uint8_t pin, uint32_t freq);
+
 #ifdef __cplusplus
 }
 #endif

variants/arduino_101/variant.cpp

@@ -98,6 +98,7 @@ PinDescription g_APinDescription[]=
     {  3,   SOC_GPIO_32, SOC_GPIO,   SOC_GPIO_AON_BASE_ADDR, 3,     GPIO_MUX_MODE, INVALID, INVALID,         INVALID, INPUT_MODE }, // Arduino IO28
 } ;
 
+uint32_t pwmPeriod[] = {PWM_PERIOD, PWM_PERIOD/2, PWM_PERIOD/2, PWM_PERIOD};
 #ifdef __cplusplus
 }
 #endif