AP_BattMonitor: added Sum backend type

this is used to combine battery monitors into a single reporting
unit. It operates on all instances beyond itself

libraries/AP_BattMonitor/AP_BattMonitor.cpp

@@ -3,6 +3,7 @@
 #include "AP_BattMonitor_SMBus.h"
 #include "AP_BattMonitor_Bebop.h"
 #include "AP_BattMonitor_BLHeliESC.h"
+#include "AP_BattMonitor_Sum.h"
 
 #include <AP_HAL/AP_HAL.h>
 
@@ -133,6 +134,9 @@ AP_BattMonitor::init()
                 drivers[instance] = new AP_BattMonitor_BLHeliESC(*this, state[instance], _params[instance]);
 #endif
                 break;
+            case AP_BattMonitor_Params::BattMonitor_TYPE_Sum:
+                drivers[instance] = new AP_BattMonitor_Sum(*this, state[instance], _params[instance], instance);
+                break;
             case AP_BattMonitor_Params::BattMonitor_TYPE_NONE:
             default:
                 break;

libraries/AP_BattMonitor/AP_BattMonitor.h

@@ -35,6 +35,7 @@ class AP_BattMonitor
     friend class AP_BattMonitor_SMBus_Solo;
     friend class AP_BattMonitor_SMBus_Maxell;
     friend class AP_BattMonitor_UAVCAN;
+    friend class AP_BattMonitor_Sum;
 
 public:
 

libraries/AP_BattMonitor/AP_BattMonitor_Params.cpp

@@ -13,7 +13,7 @@ const AP_Param::GroupInfo AP_BattMonitor_Params::var_info[] = {
     // @Param: MONITOR
     // @DisplayName: Battery monitoring
     // @Description: Controls enabling monitoring of the battery's voltage and current
-    // @Values: 0:Disabled,3:Analog Voltage Only,4:Analog Voltage and Current,5:Solo,6:Bebop,7:SMBus-Maxell,8:UAVCAN-BatteryInfo,9:BLHeli ESC
+    // @Values: 0:Disabled,3:Analog Voltage Only,4:Analog Voltage and Current,5:Solo,6:Bebop,7:SMBus-Maxell,8:UAVCAN-BatteryInfo,9:BLHeli ESC,10:SumOfFollowing
     // @User: Standard
     // @RebootRequired: True
     AP_GROUPINFO_FLAGS("MONITOR", 1, AP_BattMonitor_Params, _type, BattMonitor_TYPE_NONE, AP_PARAM_FLAG_ENABLE),

libraries/AP_BattMonitor/AP_BattMonitor_Params.h

@@ -21,7 +21,8 @@ public:
         BattMonitor_TYPE_BEBOP                      = 6,
         BattMonitor_TYPE_MAXELL                     = 7,
         BattMonitor_TYPE_UAVCAN_BatteryInfo         = 8,
-        BattMonitor_TYPE_BLHeliESC                  = 9
+        BattMonitor_TYPE_BLHeliESC                  = 9,
+        BattMonitor_TYPE_Sum                        = 10,
     };
 
     // low voltage sources (used for BATT_LOW_TYPE parameter)

libraries/AP_BattMonitor/AP_BattMonitor_Sum.cpp

@@ -0,0 +1,54 @@
+#include <AP_HAL/AP_HAL.h>
+#include <AP_Common/AP_Common.h>
+#include <AP_Math/AP_Math.h>
+#include "AP_BattMonitor.h"
+#include "AP_BattMonitor_Sum.h"
+
+/*
+  battery monitor that is the sum of other battery monitors after this one
+
+  This can be used to combined other current/voltage sensors into a
+  single backend
+ */
+extern const AP_HAL::HAL& hal;
+
+/// Constructor
+AP_BattMonitor_Sum::AP_BattMonitor_Sum(AP_BattMonitor &mon,
+                                       AP_BattMonitor::BattMonitor_State &mon_state,
+                                       AP_BattMonitor_Params &params,
+                                       uint8_t instance) :
+    AP_BattMonitor_Backend(mon, mon_state, params),
+    _instance(instance)
+{
+}
+
+// read - read the voltage and current
+void
+AP_BattMonitor_Sum::read()
+{
+    float voltage_sum = 0;
+    uint8_t voltage_count = 0;
+    float current_sum = 0;
+    uint8_t current_count = 0;
+
+    for (uint8_t i=_instance+1; i<_mon.num_instances(); i++) {
+        if (!_mon.healthy(i)) {
+            continue;
+        }
+        voltage_sum += _mon.voltage(i);
+        voltage_count++;
+        if (_mon.has_current(i)) {
+            current_sum += _mon.current_amps(i);
+            current_count++;
+        }
+    }
+    if (voltage_count > 0) {
+        _state.voltage = voltage_sum / voltage_count;
+        _state.last_time_micros = AP_HAL::micros();
+    }
+    if (current_count > 0) {
+        _state.current_amps = current_sum;
+    }
+    _has_current = (current_count > 0);
+    _state.healthy = (voltage_count > 0);
+}

libraries/AP_BattMonitor/AP_BattMonitor_Sum.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "AP_BattMonitor.h"
+#include "AP_BattMonitor_Backend.h"
+
+class AP_BattMonitor_Sum : public AP_BattMonitor_Backend
+{
+public:
+
+    /// Constructor
+    AP_BattMonitor_Sum(AP_BattMonitor &mon, AP_BattMonitor::BattMonitor_State &mon_state, AP_BattMonitor_Params &params, uint8_t instance);
+
+    /// Read the battery voltage and current.  Should be called at 10hz
+    void read() override;
+
+    /// returns true if battery monitor provides consumed energy info
+    bool has_consumed_energy() const override { return has_current(); }
+
+    /// returns true if battery monitor provides current info
+    bool has_current() const override { return _has_current; }
+
+    void init(void) override {}
+
+private:
+    uint8_t _instance;
+    bool _has_current;
+};