Allow to change default PWM frequency

Default is PWM_FREQUENCY (1000Hz).
Call `analogWriteFrequency(freq)` before `analogWrite(pin, val)`
to use the new frequency.

Note that no compute/check is performed to ensure the requested freq.
This is dependent on how the computation is currently done in analogWrite.
This limitation will be remove when Timer management will be done.

Signed-off-by: Frederic.Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/wiring_analog.c

@@ -29,6 +29,7 @@ uint32_t g_anOutputPinConfigured[MAX_NB_PORT] = {0};
 
 static int _readResolution = 10;
 static int _writeResolution = 8;
+static uint32_t _writeFreq = PWM_FREQUENCY;
 
 void analogReadResolution(int res)
 {
@@ -40,6 +41,11 @@ void analogWriteResolution(int res)
   _writeResolution = res;
 }
 
+void analogWriteFrequency(uint32_t freq)
+{
+  _writeFreq = freq;
+}
+
 static inline uint32_t mapResolution(uint32_t value, uint32_t from, uint32_t to)
 {
   if (from == to) {
@@ -97,7 +103,7 @@ void analogWrite(uint32_t ulPin, uint32_t ulValue)
           set_pin_configured(p, g_anOutputPinConfigured);
         }
         ulValue = mapResolution(ulValue, _writeResolution, PWM_RESOLUTION);
-        pwm_start(p, PWM_FREQUENCY * PWM_MAX_DUTY_CYCLE,
+        pwm_start(p, _writeFreq * PWM_MAX_DUTY_CYCLE,
                   PWM_MAX_DUTY_CYCLE,
                   ulValue, do_init);
       } else { //DIGITAL PIN ONLY

cores/arduino/wiring_analog.h

@@ -69,6 +69,14 @@ extern void analogReadResolution(int res);
  */
 extern void analogWriteResolution(int res);
 
+/*
+ * \brief Set the frequency of analogWrite. Default is PWM_FREQUENCY (1000) in Hertz.
+ *
+ * \param freq
+ */
+extern void analogWriteFrequency(uint32_t freq);
+
+
 extern void analogOutputInit(void) ;
 
 #ifdef __cplusplus