BATTERY_STATUS: improve filling cell voltage

according to review comment

src/lib/mathlib/math/Limits.hpp

@@ -56,6 +56,12 @@ constexpr _Tp min(_Tp a, _Tp b)
 	return (a < b) ? a : b;
 }
 
+template<typename _Tp>
+constexpr _Tp min(_Tp a, _Tp b, _Tp c)
+{
+	return min(min(a, b), c);
+}
+
 template<typename _Tp>
 constexpr _Tp max(_Tp a, _Tp b)
 {

src/modules/mavlink/streams/BATTERY_STATUS.hpp

@@ -115,8 +115,8 @@ private:
 				}
 
 				// fill cell voltages
-				static constexpr uint8_t mavlink_cell_slots = (sizeof(bat_msg.voltages) / sizeof(bat_msg.voltages[0]));
-				static constexpr uint8_t mavlink_cell_slots_extension
+				static constexpr int mavlink_cell_slots = (sizeof(bat_msg.voltages) / sizeof(bat_msg.voltages[0]));
+				static constexpr int mavlink_cell_slots_extension
 					= (sizeof(bat_msg.voltages_ext) / sizeof(bat_msg.voltages_ext[0]));
 				uint16_t cell_voltages[mavlink_cell_slots + mavlink_cell_slots_extension];
 
@@ -124,28 +124,32 @@ private:
 					voltage = UINT16_MAX;
 				}
 
-				// We don't know the cell count or we don't know the indpendent cell voltages so we report the total voltage in the first cell
-				if (battery_status.cell_count == 0 || battery_status.voltage_cell_v[0] < 0.0001f) {
-					cell_voltages[0] = battery_status.voltage_filtered_v * 1000.f;
+				if (battery_status.connected) {
+					// We don't know the cell count or we don't know the indpendent cell voltages so we report the total voltage in the first cell
+					if (battery_status.cell_count == 0 || battery_status.voltage_cell_v[0] < 0.0001f) {
+						cell_voltages[0] = battery_status.voltage_filtered_v * 1000.f;
 
-				} else {
-					static constexpr uint8_t uorb_cell_slots =
-						(sizeof(battery_status.voltage_cell_v) / sizeof(battery_status.voltage_cell_v[0]));
+					} else {
+						static constexpr int uorb_cell_slots =
+							(sizeof(battery_status.voltage_cell_v) / sizeof(battery_status.voltage_cell_v[0]));
+
+						const int cell_slots = math::min(static_cast<int>(battery_status.cell_count),
+										 uorb_cell_slots,
+										 mavlink_cell_slots + mavlink_cell_slots_extension);
 
-					for (uint8_t cell = 0; cell < mavlink_cell_slots + mavlink_cell_slots_extension; cell++) {
-						if (battery_status.connected && cell < math::min(battery_status.cell_count, uorb_cell_slots)) {
+						for (int cell = 0; cell < cell_slots; cell++) {
 							cell_voltages[cell] = battery_status.voltage_cell_v[cell] * 1000.f;
 						}
 					}
 				}
 
 				// voltage fields 1-10
-				for (uint8_t cell = 0; cell < mavlink_cell_slots; cell++) {
+				for (int cell = 0; cell < mavlink_cell_slots; cell++) {
 					bat_msg.voltages[cell] = cell_voltages[cell];
 				}
 
 				// voltage fields 11-14 into the extension
-				for (uint8_t cell = 0; cell < mavlink_cell_slots_extension; cell++) {
+				for (int cell = 0; cell < mavlink_cell_slots_extension; cell++) {
 					bat_msg.voltages_ext[cell] = cell_voltages[mavlink_cell_slots + cell];
 				}