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connectivity/FEATURE_BLE/include/ble/services/BatteryService.h

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+/* mbed Microcontroller Library
+ * Copyright (c) 2006-2020 ARM Limited
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef MBED_BLE_BATTERY_SERVICE_H__
+#define MBED_BLE_BATTERY_SERVICE_H__
+
+#if BLE_FEATURE_GATT_SERVER
+
+#include "platform/mbed_assert.h"
+
+#include "ble/BLE.h"
+#include "ble/Gap.h"
+#include "ble/GattServer.h"
+
+/**
+ * BLE Battery service.
+ *
+ * @par purpose
+ *
+ * The battery service exposes the charge level of the battery of the device.
+ * This information is exposed as a percentage from 0% to 100%; a value of 0%
+ * represents a fully discharged battery, and a value of 100% represents a
+ * fully charged battery.
+ *
+ * Clients can read the current charge level and subscribe to server initiated
+ * updates of the charge level. The server delivers these updates to the subscribed
+ * client in a notification packet.
+ *
+ * The subscription mechanism is useful to save power; it avoids unecessary data
+ * traffic between the client and the server, which may be induced by polling the
+ * battery level characteristic value.
+ *
+ * @par usage
+ *
+ * When this class is instantiated, it adds a battery service in the GattServer.
+ *
+ * The application code can use the function updateBatteryLevel() to update the
+ * charge level that the service exposes and to notify the subscribed client that the
+ * value changed.
+ *
+ * @note You can find specification of the battery service here:
+ * https://www.bluetooth.com/specifications/gatt
+ *
+ * @attention Multiple instances of this battery service are not supported.
+ */
+class BatteryService {
+public:
+    /**
+     * Instantiate a battery service.
+     *
+     * The construction of a BatteryService adds a GATT battery service in @p
+     * _ble GattServer and sets the initial charge level of the battery to @p
+     * level.
+     *
+     * @param[in] _ble BLE device which will host the battery service.
+     * @param[in] level Initial charge level of the battery. It is a percentage
+     * where 0% means that the battery is fully discharged and 100% means that
+     * the battery is fully charged.
+     */
+    BatteryService(BLE &_ble, uint8_t level = 100) :
+        ble(_ble),
+        batteryLevel(level),
+        batteryLevelCharacteristic(
+            GattCharacteristic::UUID_BATTERY_LEVEL_CHAR,
+            &batteryLevel,
+            GattCharacteristic::BLE_GATT_CHAR_PROPERTIES_NOTIFY
+        )
+    {
+        MBED_ASSERT(level <= 100);
+        GattCharacteristic *charTable[] = { &batteryLevelCharacteristic };
+        GattService batteryService(
+            GattService::UUID_BATTERY_SERVICE,
+            charTable,
+            sizeof(charTable) / sizeof(GattCharacteristic *)
+        );
+
+        ble.gattServer().addService(batteryService);
+    }
+
+    /**
+     * Update the battery charge level that the service exposes.
+     *
+     * The server sends a notification of the new value to clients that have
+     * subscribed to the battery level characteristic updates, and clients
+     * reading the charge level after the update obtain the updated value.
+     *
+     * @param newLevel Charge level of the battery. It is a percentage of the
+     * remaining charge between 0% and 100%.
+     *
+     * @attention This function must be called in the execution context of the
+     * BLE stack.
+     */
+    void updateBatteryLevel(uint8_t newLevel)
+    {
+        MBED_ASSERT(newLevel <= 100);
+        batteryLevel = newLevel;
+        ble.gattServer().write(
+            batteryLevelCharacteristic.getValueHandle(),
+            &batteryLevel,
+            1
+        );
+    }
+
+protected:
+    /**
+     * Reference to the underlying BLE instance that this object is attached to.
+     *
+     * The services and characteristics are registered in the GattServer of
+     * this BLE instance.
+     */
+    BLE &ble;
+
+    /**
+     * The current battery level represented as an integer from 0% to 100%.
+     */
+    uint8_t batteryLevel;
+
+    /**
+     * The GATT characteristic, which exposes the charge level.
+     */
+    ReadOnlyGattCharacteristic<uint8_t> batteryLevelCharacteristic;
+};
+
+#endif // BLE_FEATURE_GATT_SERVER
+
+#endif /* #ifndef MBED_BLE_BATTERY_SERVICE_H__*/