Added frequency limits

drivers/servo/servo.cpp

@@ -71,7 +71,6 @@ namespace servo {
     pwm_set_gpio_level(pin, (uint16_t)ServoState::pulse_to_level(new_pulse, pwm_period, pwm_frequency));
   }
 
-
   float Servo::get_frequency() const {
     return pwm_frequency;
   }
@@ -79,6 +78,7 @@ namespace servo {
   bool Servo::set_frequency(float freq) {
     bool success = false;
 
+    if((freq >= MIN_FREQUENCY) && (freq <= MAX_FREQUENCY)) {
       // Calculate a suitable pwm wrap period for this frequency
       uint16_t period; uint16_t div16;
       if(Servo::calculate_pwm_factors(freq, period, div16)) {
@@ -115,6 +115,7 @@ namespace servo {
 
         success = true;
       }
+    }
     return success;
   }
 

drivers/servo/servo.hpp

@@ -11,9 +11,12 @@ namespace servo {
     // Constants
     //--------------------------------------------------
   public:
-    static const uint16_t DEFAULT_FREQUENCY = 50;       //The standard servo update rate
+    static constexpr float DEFAULT_FREQUENCY = 50.0f;       // The standard servo update rate
 
   private:
+    static constexpr float MIN_FREQUENCY = 10.0f;           // Lowest achievable with hardware PWM with good resolution
+    static constexpr float MAX_FREQUENCY = 350.0f;          // Highest nice value that still allows the full uS pulse range
+                                                            // Some servos are rated for 333Hz for instance
     static const uint32_t MAX_PWM_WRAP = UINT16_MAX;
 
 

micropython/modules/servo/servo.cpp

@@ -664,7 +664,7 @@ extern mp_obj_t Servo_frequency(size_t n_args, const mp_obj_t *pos_args, mp_map_
         float freq = mp_obj_get_float(args[ARG_freq].u_obj);
 
         if(!self->servo->set_frequency(freq))
-            mp_raise_ValueError("freq out of range");
+            mp_raise_ValueError("freq out of range. Expected 10Hz to 350Hz");
         else
             return mp_const_none;
     }