AP_RPM: Add Minimum RPM parameter

libraries/AP_RPM/AP_RPM.cpp

@@ -40,6 +40,12 @@ const AP_Param::GroupInfo AP_RPM::var_info[] = {
     // @Increment: 1
     AP_GROUPINFO("_MAX", 2, AP_RPM, _maximum[0], 0),
 
+    // @Param: _MIN
+    // @DisplayName: Minimum RPM
+    // @Description: Minimum RPM to report
+    // @Increment: 1
+    AP_GROUPINFO("_MIN", 3, AP_RPM, _minimum[0], 0),
+
 #if RPM_MAX_INSTANCES > 1
     // @Param: 2_TYPE
     // @DisplayName: Second RPM type

libraries/AP_RPM/AP_RPM.h

@@ -52,6 +52,7 @@ public:
     AP_Int8  _type[RPM_MAX_INSTANCES];
     AP_Float _scaling[RPM_MAX_INSTANCES];
     AP_Float _maximum[RPM_MAX_INSTANCES];
+    AP_Float _minimum[RPM_MAX_INSTANCES];
 
     static const struct AP_Param::GroupInfo var_info[];
     

libraries/AP_RPM/RPM_PX4_PWM.cpp

@@ -82,6 +82,7 @@ void AP_RPM_PX4_PWM::update(void)
     uint16_t count = 0;
     const float scaling = ap_rpm._scaling[state.instance];
     float maximum = ap_rpm._maximum[state.instance];
+    float minimum = ap_rpm._minimum[state.instance];
     float quality = 0;
 
     while (::read(_fd, &pwm, sizeof(pwm)) == sizeof(pwm)) {
@@ -91,7 +92,7 @@ void AP_RPM_PX4_PWM::update(void)
         }
         float rpm = scaling * (1.0e6f * 60) / pwm.period;
         float filter_value = signal_quality_filter.get();
-        if (maximum <= 0 || rpm <= maximum) {
+        if ((maximum <= 0 || rpm <= maximum) && (rpm >= minimum)) {
             state.rate_rpm = signal_quality_filter.apply(rpm);
             if (is_zero(filter_value)){
                 quality = 0;