AP_BattMonitor: support LTC2946 I2C battery monitoring

libraries/AP_BattMonitor/AP_BattMonitor.cpp

@@ -15,6 +15,7 @@
 #include "AP_BattMonitor_Generator.h"
 #include "AP_BattMonitor_MPPT_PacketDigital.h"
 #include "AP_BattMonitor_INA231.h"
+#include "AP_BattMonitor_LTC2946.h"
 
 #include <AP_HAL/AP_HAL.h>
 
@@ -300,6 +301,11 @@ AP_BattMonitor::init()
             case Type::INA231:
                 drivers[instance] = new AP_BattMonitor_INA231(*this, state[instance], _params[instance]);
                 break;
+#endif
+#if HAL_BATTMON_LTC2946_ENABLED
+            case Type::LTC2946:
+                drivers[instance] = new AP_BattMonitor_LTC2946(*this, state[instance], _params[instance]);
+                break;
 #endif
             case Type::NONE:
             default:

libraries/AP_BattMonitor/AP_BattMonitor.h

@@ -47,6 +47,7 @@ class AP_BattMonitor_UAVCAN;
 class AP_BattMonitor_Generator;
 class AP_BattMonitor_MPPT_PacketDigital;
 class AP_BattMonitor_INA231;
+class AP_BattMonitor_LTC2946;
 
 class AP_BattMonitor
 {
@@ -64,6 +65,7 @@ class AP_BattMonitor
     friend class AP_BattMonitor_Generator;
     friend class AP_BattMonitor_MPPT_PacketDigital;
     friend class AP_BattMonitor_INA231;
+    friend class AP_BattMonitor_LTC2946;
 
 public:
 
@@ -96,6 +98,7 @@ public:
         Rotoye                     = 19,
         MPPT_PacketDigital         = 20,
         INA231                     = 21,
+        LTC2946                    = 22,
     };
 
     FUNCTOR_TYPEDEF(battery_failsafe_handler_fn_t, void, const char *, const int8_t);

libraries/AP_BattMonitor/AP_BattMonitor_LTC2946.cpp

@@ -0,0 +1,114 @@
+#include "AP_BattMonitor_LTC2946.h"
+#include <GCS_MAVLink/GCS.h>
+#include <AP_HAL/utility/sparse-endian.h>
+
+#if HAL_BATTMON_LTC2946_ENABLED
+
+extern const AP_HAL::HAL& hal;
+
+#define REG_CTRLA 0x00
+#define REG_CTRLB 0x01
+#define REG_STATUS 0x80
+#define REG_MFR_ID 0xe7
+
+// first byte of 16 bit ID is stable
+#define ID_LTC2946 0x60
+
+#define REG_DELTA 0x14 // 16 bits
+#define REG_VIN   0x1e // 16 bits
+
+#define REGA_CONF 0x18 // sense, alternate
+#define REGB_CONF 0x01 // auto-reset
+
+void AP_BattMonitor_LTC2946::init(void)
+{
+    dev = hal.i2c_mgr->get_device(HAL_BATTMON_LTC2946_BUS, HAL_BATTMON_LTC2946_ADDR, 100000, false, 20);
+    if (!dev) {
+        return;
+    }
+
+    uint8_t id = 0;
+    WITH_SEMAPHORE(dev->get_semaphore());
+    if (!dev->read_registers(REG_MFR_ID, &id, 1) || id != ID_LTC2946) {
+        GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "LTC2946: Failed to find device 0x%04x", unsigned(id));
+        return;
+    }
+
+    if (!dev->write_register(REG_CTRLA, REGA_CONF) ||
+        !dev->write_register(REG_CTRLB, REGB_CONF)) {
+        GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "LTC2946: Failed to configure device");
+        return;
+    }
+
+    // use datasheet typical values
+    voltage_LSB = 102.4 / 4095.0;
+    current_LSB = (0.1024/0.0005) / 4095.0;
+
+    GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "LTC2946: found monitor on bus %u", HAL_BATTMON_LTC2946_BUS);
+
+    if (dev) {
+        dev->register_periodic_callback(25000, FUNCTOR_BIND_MEMBER(&AP_BattMonitor_LTC2946::timer, void));
+    }
+}
+
+/// read the battery_voltage and current, should be called at 10hz
+void AP_BattMonitor_LTC2946::read(void)
+{
+    WITH_SEMAPHORE(accumulate.sem);
+    _state.healthy = accumulate.count > 0;
+    if (!_state.healthy) {
+        return;
+    }
+
+    _state.voltage = accumulate.volt_sum / accumulate.count;
+    _state.current_amps = accumulate.current_sum / accumulate.count;
+    accumulate.volt_sum = 0;
+    accumulate.current_sum = 0;
+    accumulate.count = 0;
+
+    const uint32_t tnow = AP_HAL::micros();
+    const float dt = tnow - _state.last_time_micros;
+    
+    // update total current drawn since startup
+    if (_state.last_time_micros != 0 && dt < 2000000.0) {
+        // .0002778 is 1/3600 (conversion to hours)
+        const float mah = _state.current_amps * dt * 0.0000002778;
+        _state.consumed_mah += mah;
+        _state.consumed_wh  += 0.001 * mah * _state.voltage;
+    }
+    _state.last_time_micros = tnow;
+}
+
+/*
+ read word from register
+ returns true if read was successful, false if failed
+*/
+bool AP_BattMonitor_LTC2946::read_word(const uint8_t reg, uint16_t& data) const
+{
+    // read the appropriate register from the device
+    if (!dev->read_registers(reg, (uint8_t *)&data, sizeof(data))) {
+        return false;
+    }
+
+    // convert byte order
+    data = uint16_t(be16toh(uint16_t(data)));
+
+    // return success
+    return true;
+}
+
+void AP_BattMonitor_LTC2946::timer(void)
+{
+    uint16_t amps, volts;
+    if (!read_word(REG_DELTA, amps) ||
+        !read_word(REG_VIN, volts)) {
+        return;
+    }
+    WITH_SEMAPHORE(accumulate.sem);
+    // convert 12 bit ADC data
+    accumulate.volt_sum += (volts>>4) * voltage_LSB;
+    accumulate.current_sum += (amps>>4) * current_LSB;
+    accumulate.count++;
+}
+
+#endif // HAL_BATTMON_LTC2946_ENABLED

libraries/AP_BattMonitor/AP_BattMonitor_LTC2946.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <AP_Common/AP_Common.h>
+#include <AP_HAL/I2CDevice.h>
+#include "AP_BattMonitor_Backend.h"
+#include <utility>
+
+#define HAL_BATTMON_LTC2946_ENABLED defined(HAL_BATTMON_LTC2946_BUS) && defined(HAL_BATTMON_LTC2946_ADDR)
+
+#if HAL_BATTMON_LTC2946_ENABLED
+
+class AP_BattMonitor_LTC2946 : public AP_BattMonitor_Backend
+{
+public:
+    // inherit constructor
+    using AP_BattMonitor_Backend::AP_BattMonitor_Backend;
+
+    bool has_cell_voltages() const override { return false; }
+    bool has_temperature() const override { return false; }
+    bool has_current() const override { return true; }
+    bool reset_remaining(float percentage) override { return false; }
+    bool get_cycle_count(uint16_t &cycles) const override { return false; }
+
+    virtual void init(void) override;
+    virtual void read() override;
+    
+private:
+    AP_HAL::OwnPtr<AP_HAL::I2CDevice> dev;
+
+    bool read_word(const uint8_t reg, uint16_t& data) const;
+    void timer(void);
+
+    struct {
+        uint16_t count;
+        float volt_sum;
+        float current_sum;
+        HAL_Semaphore sem;
+    } accumulate;
+    float current_LSB;
+    float voltage_LSB;
+};
+
+#endif // HAL_BATTMON_LTC2946_ENABLED

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-Generic,8:UAVCAN-BatteryInfo,9:ESC,10:SumOfFollowing,11:FuelFlow,12:FuelLevelPWM,13:SMBUS-SUI3,14:SMBUS-SUI6,15:NeoDesign,16:SMBus-Maxell,17:Generator-Elec,18:Generator-Fuel,19:Rotoye,20:MPPT,21:INA231
+    // @Values: 0:Disabled,3:Analog Voltage Only,4:Analog Voltage and Current,5:Solo,6:Bebop,7:SMBus-Generic,8:UAVCAN-BatteryInfo,9:ESC,10:SumOfFollowing,11:FuelFlow,12:FuelLevelPWM,13:SMBUS-SUI3,14:SMBUS-SUI6,15:NeoDesign,16:SMBus-Maxell,17:Generator-Elec,18:Generator-Fuel,19:Rotoye,20:MPPT,21:INA231,22:LTC2946
     // @User: Standard
     // @RebootRequired: True
     AP_GROUPINFO_FLAGS("MONITOR", 1, AP_BattMonitor_Params, _type, int8_t(AP_BattMonitor::Type::NONE), AP_PARAM_FLAG_ENABLE),