AP_BattMonitor: added reset_remaining() API

used to allow battery swap before takeoff

libraries/AP_BattMonitor/AP_BattMonitor.cpp

@@ -494,6 +494,21 @@ void AP_BattMonitor::checkPoweringOff(void)
     }
 }
 
+/*
+  reset battery remaining percentage for batteries that integrate to
+  calculate percentage remaining
+*/
+bool AP_BattMonitor::reset_remaining(uint16_t battery_mask, float percentage)
+{
+    bool ret = true;
+    for (uint8_t i = 0; i < _num_instances; i++) {
+        if ((1U<<i) & battery_mask) {
+            ret &= drivers[i]->reset_remaining(percentage);
+        }
+    }
+    return ret;
+}
+
 namespace AP {
 
 AP_BattMonitor &battery()

libraries/AP_BattMonitor/AP_BattMonitor.h

@@ -167,6 +167,9 @@ public:
     // sends powering off mavlink broadcasts and sets notify flag
     void checkPoweringOff(void);
 
+    // reset battery remaining percentage
+    bool reset_remaining(uint16_t battery_mask, float percentage);
+
     static const struct AP_Param::GroupInfo var_info[];
 
 protected:

libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp

@@ -215,3 +215,22 @@ void AP_BattMonitor_Backend::check_failsafe_types(bool &low_voltage, bool &low_c
         low_capacity = false;
     }
 }
+
+/*
+  default implementation for reset_remaining(). This sets consumed_wh
+  and consumed_mah based on the given percentage. Use percentage=100
+  for a full battery
+*/
+bool AP_BattMonitor_Backend::reset_remaining(float percentage)
+{
+    percentage = constrain_float(percentage, 0, 100);
+    const float used_proportion = (100 - percentage) * 0.01;
+    _state.consumed_mah = used_proportion * _params._pack_capacity;
+    // without knowing the history we can't do consumed_wh
+    // accurately. Best estimate is based on current voltage. This
+    // will be good when resetting the battery to a value close to
+    // full charge
+    _state.consumed_wh = _state.consumed_mah * 1000 * _state.voltage;
+
+    return true;
+}

libraries/AP_BattMonitor/AP_BattMonitor_Backend.h

@@ -59,6 +59,9 @@ public:
     // returns false if we fail arming checks, in which case the buffer will be populated with a failure message
     bool arming_checks(char * buffer, size_t buflen) const;
 
+    // reset remaining percentage to given value
+    virtual bool reset_remaining(float percentage);
+
 protected:
     AP_BattMonitor                      &_mon;      // reference to front-end
     AP_BattMonitor::BattMonitor_State   &_state;    // reference to this instances state (held in the front-end)

libraries/AP_BattMonitor/AP_BattMonitor_Bebop.h

@@ -40,6 +40,9 @@ public:
     // bebop provides current info
     bool has_current() const override { return true; };
 
+    // don't allow reset of remaining capacity for bebop battery
+    bool reset_remaining(float percentage) override { return false; }
+
 private:
     float _prev_vbat_raw;
     float _prev_vbat;

libraries/AP_BattMonitor/AP_BattMonitor_SMBus.h

@@ -42,6 +42,9 @@ public:
     // all smart batteries are expected to provide current
     bool has_current() const override { return true; }
 
+    // don't allow reset of remaining capacity for SMBus
+    bool reset_remaining(float percentage) override { return false; }
+    
     void init(void) override;
 
 protected: