Introducing the Adafruit nRF52840 Feather

by lady ada

published January 02, 2019, last updated September 11, 2024

posted in CircuitPython Feather/ Feather Boards Internet of Things - IOT/ Bluefruit / BLE

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Updated

Intermediate

Product guide

BLEService

The Bluefruit nRF52 BSP codebase is undergoing active development based on customer feedback and testing. As such, the class documentation here is incomplete, and you should consult the Github repo for the latest code and API developments: https://goo.gl/LdEx62

This base class is used when defining custom BLE Gatt Services, such as the various service helper classes that make up the Adafruit Bluefruit nRF52 API described here.

Unless you are implementing a custom GATT service and characteristic, you normally won't use this base class directly, and would instantiate and call a higher level helper service or characteristic included in the Bluefruit nRF52 API.

Basic Usage

There are normally only two operation required to use the BLEService class:

You need to declare and instantiate the class with an appropriate 16-bit or 128-bit UUID in the constructor:

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BLEService myService = BLEService(0x1234);

BLEService myService = BLEService(0x1234);

You then need to call the .begin() method on the instance before adding any BLECharacteristics to it (via the BLECharacteristic's respective .begin() function call):

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myService.begin();

myService.begin();

Order of Operations (Important!)

One very important thing to take into consideration when working with BLEService and BLECharacteristic, is that any BLECharacteristic will automatically be added to the last BLEService that had it's `.begin()` function called. As such, you must call yourService.begin() before adding any characteristics!

See the example at the bottom of this page for a concrete example of how this works in practice.

API

BLEService has the following overall class structure:

This documentation may be slightly out of date as bugs are fixed, and the API develops. You should always consult the Github repo for the definitive latest code release and class definitions!

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BLEUuid uuid;

static BLEService* lastService;

BLEService(void);
BLEService(uint16_t uuid16);
BLEService(uint8_t const  uuid128[]);

void setUuid(uint16_t uuid16);
void setUuid(uint8_t const  uuid128[]);

virtual err_t begin(void);

BLEUuid uuid;

static BLEService* lastService;

BLEService(void);
BLEService(uint16_t uuid16);
BLEService(uint8_t const  uuid128[]);

void setUuid(uint16_t uuid16);
void setUuid(uint8_t const  uuid128[]);

virtual err_t begin(void);

Example

The following example declares a HRM (Heart Rate Monitor) service, and assigns some characteristics to it:

Note that this example code is incomplete. For the full example open the 'custom_hrm' example that is part of the nRF52 BSP! The code below is for illustration purposes only.

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/* HRM Service Definitions
 * Heart Rate Monitor Service:  0x180D
 * Heart Rate Measurement Char: 0x2A37
 * Body Sensor Location Char:   0x2A38
 */
BLEService        hrms = BLEService(UUID16_SVC_HEART_RATE);
BLECharacteristic hrmc = BLECharacteristic(UUID16_CHR_HEART_RATE_MEASUREMENT);
BLECharacteristic bslc = BLECharacteristic(UUID16_CHR_BODY_SENSOR_LOCATION);

void setupHRM(void)
{
  // Configure the Heart Rate Monitor service
  // See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.service.heart_rate.xml
  // Supported Characteristics:
  // Name                         UUID    Requirement Properties
  // ---------------------------- ------  ----------- ----------
  // Heart Rate Measurement       0x2A37  Mandatory   Notify
  // Body Sensor Location         0x2A38  Optional    Read
  // Heart Rate Control Point     0x2A39  Conditional Write       <-- Not used here
  hrms.begin();

  // Note: You must call .begin() on the BLEService before calling .begin() on
  // any characteristic(s) within that service definition.. Calling .begin() on
  // a BLECharacteristic will cause it to be added to the last BLEService that
  // was 'begin()'ed!

  // Configure the Heart Rate Measurement characteristic
  // See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.heart_rate_measurement.xml
  // Permission = Notify
  // Min Len    = 1
  // Max Len    = 8
  //    B0      = UINT8  - Flag (MANDATORY)
  //      b5:7  = Reserved
  //      b4    = RR-Internal (0 = Not present, 1 = Present)
  //      b3    = Energy expended status (0 = Not present, 1 = Present)
  //      b1:2  = Sensor contact status (0+1 = Not supported, 2 = Supported but contact not detected, 3 = Supported and detected)
  //      b0    = Value format (0 = UINT8, 1 = UINT16)
  //    B1      = UINT8  - 8-bit heart rate measurement value in BPM
  //    B2:3    = UINT16 - 16-bit heart rate measurement value in BPM
  //    B4:5    = UINT16 - Energy expended in joules
  //    B6:7    = UINT16 - RR Internal (1/1024 second resolution)
  hrmc.setProperties(CHR_PROPS_NOTIFY);
  hrmc.setPermission(SECMODE_OPEN, SECMODE_NO_ACCESS);
  hrmc.setFixedLen(2);
  hrmc.setCccdWriteCallback(cccd_callback);  // Optionally capture CCCD updates
  hrmc.begin();
  uint8_t hrmdata[2] = { 0b00000110, 0x40 }; // Set the characteristic to use 8-bit values, with the sensor connected and detected
  hrmc.notify(hrmdata, 2);                   // Use .notify instead of .write!

  // Configure the Body Sensor Location characteristic
  // See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.body_sensor_location.xml
  // Permission = Read
  // Min Len    = 1
  // Max Len    = 1
  //    B0      = UINT8 - Body Sensor Location
  //      0     = Other
  //      1     = Chest
  //      2     = Wrist
  //      3     = Finger
  //      4     = Hand
  //      5     = Ear Lobe
  //      6     = Foot
  //      7:255 = Reserved
  bslc.setProperties(CHR_PROPS_READ);
  bslc.setPermission(SECMODE_OPEN, SECMODE_NO_ACCESS);
  bslc.setFixedLen(1);
  bslc.begin();
  bslc.write8(2);    // Set the characteristic to 'Wrist' (2)
}

void cccd_callback(BLECharacteristic& chr, uint16_t cccd_value)
{
    // Display the raw request packet
    Serial.print("CCCD Updated: ");
    //Serial.printBuffer(request->data, request->len);
    Serial.print(cccd_value);
    Serial.println("");

    // Check the characteristic this CCCD update is associated with in case
    // this handler is used for multiple CCCD records.
    if (chr.uuid == hrmc.uuid) {
        if (chr.notifyEnabled()) {
            Serial.println("Heart Rate Measurement 'Notify' enabled");
        } else {
            Serial.println("Heart Rate Measurement 'Notify' disabled");
        }
    }
}

/* HRM Service Definitions
 * Heart Rate Monitor Service:  0x180D
 * Heart Rate Measurement Char: 0x2A37
 * Body Sensor Location Char:   0x2A38
 */
BLEService        hrms = BLEService(UUID16_SVC_HEART_RATE);
BLECharacteristic hrmc = BLECharacteristic(UUID16_CHR_HEART_RATE_MEASUREMENT);
BLECharacteristic bslc = BLECharacteristic(UUID16_CHR_BODY_SENSOR_LOCATION);

void setupHRM(void)
{
  // Configure the Heart Rate Monitor service
  // See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.service.heart_rate.xml
  // Supported Characteristics:
  // Name                         UUID    Requirement Properties
  // ---------------------------- ------  ----------- ----------
  // Heart Rate Measurement       0x2A37  Mandatory   Notify
  // Body Sensor Location         0x2A38  Optional    Read
  // Heart Rate Control Point     0x2A39  Conditional Write       <-- Not used here
  hrms.begin();

  // Note: You must call .begin() on the BLEService before calling .begin() on
  // any characteristic(s) within that service definition.. Calling .begin() on
  // a BLECharacteristic will cause it to be added to the last BLEService that
  // was 'begin()'ed!

  // Configure the Heart Rate Measurement characteristic
  // See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.heart_rate_measurement.xml
  // Permission = Notify
  // Min Len    = 1
  // Max Len    = 8
  //    B0      = UINT8  - Flag (MANDATORY)
  //      b5:7  = Reserved
  //      b4    = RR-Internal (0 = Not present, 1 = Present)
  //      b3    = Energy expended status (0 = Not present, 1 = Present)
  //      b1:2  = Sensor contact status (0+1 = Not supported, 2 = Supported but contact not detected, 3 = Supported and detected)
  //      b0    = Value format (0 = UINT8, 1 = UINT16)
  //    B1      = UINT8  - 8-bit heart rate measurement value in BPM
  //    B2:3    = UINT16 - 16-bit heart rate measurement value in BPM
  //    B4:5    = UINT16 - Energy expended in joules
  //    B6:7    = UINT16 - RR Internal (1/1024 second resolution)
  hrmc.setProperties(CHR_PROPS_NOTIFY);
  hrmc.setPermission(SECMODE_OPEN, SECMODE_NO_ACCESS);
  hrmc.setFixedLen(2);
  hrmc.setCccdWriteCallback(cccd_callback);  // Optionally capture CCCD updates
  hrmc.begin();
  uint8_t hrmdata[2] = { 0b00000110, 0x40 }; // Set the characteristic to use 8-bit values, with the sensor connected and detected
  hrmc.notify(hrmdata, 2);                   // Use .notify instead of .write!

  // Configure the Body Sensor Location characteristic
  // See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.body_sensor_location.xml
  // Permission = Read
  // Min Len    = 1
  // Max Len    = 1
  //    B0      = UINT8 - Body Sensor Location
  //      0     = Other
  //      1     = Chest
  //      2     = Wrist
  //      3     = Finger
  //      4     = Hand
  //      5     = Ear Lobe
  //      6     = Foot
  //      7:255 = Reserved
  bslc.setProperties(CHR_PROPS_READ);
  bslc.setPermission(SECMODE_OPEN, SECMODE_NO_ACCESS);
  bslc.setFixedLen(1);
  bslc.begin();
  bslc.write8(2);    // Set the characteristic to 'Wrist' (2)
}

void cccd_callback(BLECharacteristic& chr, uint16_t cccd_value)
{
    // Display the raw request packet
    Serial.print("CCCD Updated: ");
    //Serial.printBuffer(request->data, request->len);
    Serial.print(cccd_value);
    Serial.println("");

    // Check the characteristic this CCCD update is associated with in case
    // this handler is used for multiple CCCD records.
    if (chr.uuid == hrmc.uuid) {
        if (chr.notifyEnabled()) {
            Serial.println("Heart Rate Measurement 'Notify' enabled");
        } else {
            Serial.println("Heart Rate Measurement 'Notify' disabled");
        }
    }
}

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