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HeartRateService.h
1 /* mbed Microcontroller Library
2  * Copyright (c) 2006-2020 ARM Limited
3  *
4  * SPDX-License-Identifier: Apache-2.0
5  *
6  * Licensed under the Apache License, Version 2.0 (the "License");
7  * you may not use this file except in compliance with the License.
8  * You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18 
19 #ifndef MBED_BLE_HEART_RATE_SERVICE_H__
20 #define MBED_BLE_HEART_RATE_SERVICE_H__
21 
22 #include "ble/BLE.h"
23 #include "ble/Gap.h"
24 #include "ble/GattServer.h"
25 
26 #if BLE_FEATURE_GATT_SERVER
27 
28 /**
29  * BLE Heart Rate Service.
30  *
31  * @par purpose
32  *
33  * Fitness applications use the heart rate service to expose the heart
34  * beat per minute measured by a heart rate sensor.
35  *
36  * Clients can read the intended location of the sensor and the last heart rate
37  * value measured. Additionally, clients can subscribe to server initiated
38  * updates of the heart rate value measured by the sensor. The service delivers
39  * these updates to the subscribed client in a notification packet.
40  *
41  * The subscription mechanism is useful to save power; it avoids unecessary data
42  * traffic between the client and the server, which may be induced by polling the
43  * value of the heart rate measurement characteristic.
44  *
45  * @par usage
46  *
47  * When this class is instantiated, it adds a heart rate service in the GattServer.
48  * The service contains the location of the sensor and the initial value measured
49  * by the sensor.
50  *
51  * Application code can invoke updateHeartRate() when a new heart rate measurement
52  * is acquired; this function updates the value of the heart rate measurement
53  * characteristic and notifies the new value to subscribed clients.
54  *
55  * @note You can find specification of the heart rate service here:
56  * https://www.bluetooth.com/specifications/gatt
57  *
58  * @attention The service does not expose information related to the sensor
59  * contact, the accumulated energy expanded or the interbeat intervals.
60  *
61  * @attention The heart rate profile limits the number of instantiations of the
62  * heart rate services to one.
63  */
65 public:
66  /**
67  * Intended location of the heart rate sensor.
68  */
70  /**
71  * Other location.
72  */
74 
75  /**
76  * Chest.
77  */
79 
80  /**
81  * Wrist.
82  */
84 
85  /**
86  * Finger.
87  */
89 
90  /**
91  * Hand.
92  */
94 
95  /**
96  * Earlobe.
97  */
99 
100  /**
101  * Foot.
102  */
104  };
105 
106 public:
107  /**
108  * Construct and initialize a heart rate service.
109  *
110  * The construction process adds a GATT heart rate service in @p _ble
111  * GattServer, sets the value of the heart rate measurement characteristic
112  * to @p hrmCounter and the value of the body sensor location characteristic
113  * to @p location.
114  *
115  * @param[in] _ble BLE device that hosts the heart rate service.
116  * @param[in] hrmCounter Heart beats per minute measured by the heart rate
117  * sensor.
118  * @param[in] location Intended location of the heart rate sensor.
119  */
120  HeartRateService(BLE &_ble, uint16_t hrmCounter, BodySensorLocation location) :
121  ble(_ble),
122  valueBytes(hrmCounter),
123  hrmRate(
124  GattCharacteristic::UUID_HEART_RATE_MEASUREMENT_CHAR,
125  valueBytes.getPointer(),
126  valueBytes.getNumValueBytes(),
127  HeartRateValueBytes::MAX_VALUE_BYTES,
128  GattCharacteristic::BLE_GATT_CHAR_PROPERTIES_NOTIFY
129  ),
130  hrmLocation(
131  GattCharacteristic::UUID_BODY_SENSOR_LOCATION_CHAR,
132  reinterpret_cast<uint8_t*>(&location)
133  )
134  {
135  setupService();
136  }
137 
138  /**
139  * Update the heart rate that the service exposes.
140  *
141  * The server sends a notification of the new value to clients that have
142  * subscribed to updates of the heart rate measurement characteristic; clients
143  * reading the heart rate measurement characteristic after the update obtain
144  * the updated value.
145  *
146  * @param[in] hrmCounter Heart rate measured in BPM.
147  *
148  * @attention This function must be called in the execution context of the
149  * BLE stack.
150  */
151  void updateHeartRate(uint16_t hrmCounter) {
152  valueBytes.updateHeartRate(hrmCounter);
153  ble.gattServer().write(
154  hrmRate.getValueHandle(),
155  valueBytes.getPointer(),
156  valueBytes.getNumValueBytes()
157  );
158  }
159 
160 protected:
161  /**
162  * Construct and add to the GattServer the heart rate service.
163  */
164  void setupService() {
165  GattCharacteristic *charTable[] = {
166  &hrmRate,
167  &hrmLocation
168  };
169  GattService hrmService(
171  charTable,
172  sizeof(charTable) / sizeof(charTable[0])
173  );
174 
175  ble.gattServer().addService(hrmService);
176  }
177 
178 protected:
179  /*
180  * Heart rate measurement value.
181  */
183  /* 1 byte for the Flags, and up to two bytes for heart rate value. */
184  static const unsigned MAX_VALUE_BYTES = 3;
185  static const unsigned FLAGS_BYTE_INDEX = 0;
186 
187  static const unsigned VALUE_FORMAT_BITNUM = 0;
188  static const uint8_t VALUE_FORMAT_FLAG = (1 << VALUE_FORMAT_BITNUM);
189 
190  HeartRateValueBytes(uint16_t hrmCounter) : valueBytes()
191  {
192  updateHeartRate(hrmCounter);
193  }
194 
195  void updateHeartRate(uint16_t hrmCounter)
196  {
197  if (hrmCounter <= 255) {
198  valueBytes[FLAGS_BYTE_INDEX] &= ~VALUE_FORMAT_FLAG;
199  valueBytes[FLAGS_BYTE_INDEX + 1] = hrmCounter;
200  } else {
201  valueBytes[FLAGS_BYTE_INDEX] |= VALUE_FORMAT_FLAG;
202  valueBytes[FLAGS_BYTE_INDEX + 1] = (uint8_t)(hrmCounter & 0xFF);
203  valueBytes[FLAGS_BYTE_INDEX + 2] = (uint8_t)(hrmCounter >> 8);
204  }
205  }
206 
207  uint8_t *getPointer()
208  {
209  return valueBytes;
210  }
211 
212  const uint8_t *getPointer() const
213  {
214  return valueBytes;
215  }
216 
217  unsigned getNumValueBytes() const
218  {
219  if (valueBytes[FLAGS_BYTE_INDEX] & VALUE_FORMAT_FLAG) {
220  return 1 + sizeof(uint16_t);
221  } else {
222  return 1 + sizeof(uint8_t);
223  }
224  }
225 
226  private:
227  uint8_t valueBytes[MAX_VALUE_BYTES];
228  };
229 
230 protected:
231  BLE &ble;
232  HeartRateValueBytes valueBytes;
233  GattCharacteristic hrmRate;
235 };
236 
237 #endif // BLE_FEATURE_GATT_SERVER
238 
239 #endif /* #ifndef MBED_BLE_HEART_RATE_SERVICE_H__*/
BodySensorLocation
Intended location of the heart rate sensor.
BLE Heart Rate Service.
GattAttribute::Handle_t getValueHandle() const
Get the characteristic&#39;s value attribute handle in the ATT table.
HeartRateService(BLE &_ble, uint16_t hrmCounter, BodySensorLocation location)
Construct and initialize a heart rate service.
UUID of the Heart Rate service.
Representation of a GattServer characteristic.
void setupService()
Construct and add to the GattServer the heart rate service.
Representation of a GattServer service.
Entry namespace for all BLE API definitions.
void updateHeartRate(uint16_t hrmCounter)
Update the heart rate that the service exposes.
Abstract away BLE-capable radio transceivers or SOCs.
Definition: BLE.h:137
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