AP_BattMonitor: allow INA2xx battery monitors to be powered after boot

the device doesn't show up till main battery is connected, so we need
this change to allow for separate avionics battery and main battery
with avionics battery powered on first

libraries/AP_BattMonitor/AP_BattMonitor_Backend.cpp

@@ -176,7 +176,8 @@ bool AP_BattMonitor_Backend::arming_checks(char * buffer, size_t buflen) const
                                 is_positive(_params._low_voltage) &&
                                 (_params._low_voltage < _params._critical_voltage);
 
-    bool result =      update_check(buflen, buffer, below_arming_voltage, "below minimum arming voltage");
+    bool result = update_check(buflen, buffer, !_state.healthy, "unhealthy");
+    result = result && update_check(buflen, buffer, below_arming_voltage, "below minimum arming voltage");
     result = result && update_check(buflen, buffer, below_arming_capacity, "below minimum arming capacity");
     result = result && update_check(buflen, buffer, low_voltage,  "low voltage failsafe");
     result = result && update_check(buflen, buffer, low_capacity, "low capacity failsafe");
@@ -184,7 +185,6 @@ bool AP_BattMonitor_Backend::arming_checks(char * buffer, size_t buflen) const
     result = result && update_check(buflen, buffer, critical_capacity, "critical capacity failsafe");
     result = result && update_check(buflen, buffer, fs_capacity_inversion, "capacity failsafe critical > low");
     result = result && update_check(buflen, buffer, fs_voltage_inversion, "voltage failsafe critical > low");
-    result = result && update_check(buflen, buffer, !_state.healthy, "unhealthy");
 
     return result;
 }

libraries/AP_BattMonitor/AP_BattMonitor_INA2xx.cpp

@@ -61,14 +61,19 @@ void AP_BattMonitor_INA2XX::init(void)
     if (!dev) {
         return;
     }
+    // register now and configure in the timer callbacks
+    dev->register_periodic_callback(25000, FUNCTOR_BIND_MEMBER(&AP_BattMonitor_INA2XX::timer, void));
+}
+
+void AP_BattMonitor_INA2XX::configure(void)
+{
+    WITH_SEMAPHORE(dev->get_semaphore());
 
     int16_t config = 0;
-    WITH_SEMAPHORE(dev->get_semaphore());
     if (!write_word(REG_CONFIG, REG_CONFIG_RESET) ||
         !write_word(REG_CONFIG, REG_CONFIG_DEFAULT) ||
         !read_word(REG_CONFIG, config) ||
         config != REG_CONFIG_DEFAULT) {
-        GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "INA2XX: Failed to find device 0x%04x", unsigned(config));
         return;
     }
 
@@ -81,16 +86,10 @@ void AP_BattMonitor_INA2XX::init(void)
     if (!write_word(REG_CONFIG, REG_CONFIG_RESET) || // reset
         !write_word(REG_CONFIG, conf) ||
         !write_word(REG_CALIBRATION, cal)) {
-        GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "INA2XX: Failed to configure device");
         return;
     }
 
-
-    GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "INA2XX: found monitor on I2C:%u:%02x", unsigned(i2c_bus), unsigned(i2c_address));
-
-    if (dev) {
-        dev->register_periodic_callback(25000, FUNCTOR_BIND_MEMBER(&AP_BattMonitor_INA2XX::timer, void));
-    }
+    configured = true;
 }
 
 /// read the battery_voltage and current, should be called at 10hz
@@ -146,11 +145,33 @@ bool AP_BattMonitor_INA2XX::write_word(const uint8_t reg, const uint16_t data) c
 
 void AP_BattMonitor_INA2XX::timer(void)
 {
+    // allow for power-on after boot
+    if (!configured) {
+        uint32_t now = AP_HAL::millis();
+        if (now - last_configure_ms > 200) {
+            // try contacting the device at 5Hz
+            last_configure_ms = now;
+            configure();
+        }
+        if (!configured) {
+            // waiting for the device to respond
+            return;
+        }
+    }
+
     int16_t bus_voltage, current;
+
     if (!read_word(REG_BUS_VOLTAGE, bus_voltage) ||
         !read_word(REG_CURRENT, current)) {
+        failed_reads++;
+        if (failed_reads > 10) {
+            // device has disconnected, we need to reconfigure it
+            configured = false;
+        }
         return;
     }
+    failed_reads = 0;
+
     WITH_SEMAPHORE(accumulate.sem);
     accumulate.volt_sum += bus_voltage * voltage_LSB;
     accumulate.current_sum += current * current_LSB;

libraries/AP_BattMonitor/AP_BattMonitor_INA2xx.h

@@ -26,20 +26,25 @@ public:
     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;
+    void init(void) override;
+    void read() override;
 
     static const struct AP_Param::GroupInfo var_info[];
 
 private:
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> dev;
 
+    void configure(void);
     bool read_word(const uint8_t reg, int16_t& data) const;
     bool write_word(const uint8_t reg, const uint16_t data) const;
     void timer(void);
 
     AP_Int8 i2c_bus;
     AP_Int8 i2c_address;
+    bool configured;
+    bool callback_registered;
+    uint32_t failed_reads;
+    uint32_t last_configure_ms;
 
     struct {
         uint16_t count;