Bluetooth Low Energy OTAP service-profile
The Bluetooth Low Energy OTAP Service is implemented using the GATT Server which runs on the OTAP Client (GAP Peripheral).
The Bluetooth LE OTAP Service does not require any other Bluetooth LE services because it is a custom service it has a 128-bit UUID. The service has 2 custom characteristics which also have 128-bit UUIDs.
The service must be included in the GATT database of the GATT Server as described in Creating GATT database of this document.
OTAP service and characteristics
The OTAP Service has a custom 128-bit UUID which is shown below. The UUID is based on a base 128-bit UUID used for Bluetooth LE custom services and characteristics. These are shown in the tables below.
Service |
128-bit UUID |
|---|---|
Base Bluetooth Low Energy |
00000000 -ba5e-f4ee-5ca1-eb1e5e4b1ce0 |
The OTAP Service custom 128-bit UUID is built using the base UUID by replacing the most significant 4 bytes which are 0 with a value specific to the OTAP Service which is 01FF5550 in hexadecimal format.
Service |
UUID (128-bit) |
|---|---|
Bluetooth LE OTAP Service |
01ff5550 -ba5e-f4ee-5ca1-eb1e5e4b1ce0 |
The Bluetooth LE OTAP Service Characteristics UUIDs are built the same as the Bluetooth LE OTAP Service UUID starting from the base 128-bit UUID but using other values for the most significant 4 bytes.
Characteristic |
UUID (128-bit) |
Properties |
Descriptors |
|---|---|---|---|
Bluetooth LE OTAP Control Point |
01ff5551 -ba5e-f4ee-5ca1-eb1e5e4b1ce0 |
Write, Indicate |
CCC |
Bluetooth LE OTAP Data |
01ff5552 -ba5e-f4ee-5ca1-eb1e5e4b1ce0 |
Write Without Response |
- |
Both characteristics are implemented as variable length characteristics.
The Bluetooth LE OTAP Control Point Characteristic is used for exchanging OTAP commands between the OTAP Server and the OTAP Client. The OTAP Client sends commands to the OTAP Server using ATT Notifications for this characteristic and the OTAP Server sends commands to the OTAP Client by making ATT Write Requests to this characteristic. Both ATT Writes and ATT Notifications are acknowledged operations via ATT Write Responses and ATT Confirmations.
The Bluetooth LE OTAP Data characteristic is used by the OTAP Server to send parts of the OTAP image file to the OTAP Client when the ATT transfer method is chosen by the application. The ATT Write Commands (GATT Write Without Response operation) is not an acknowledged operation.
The Bluetooth LE OTAP service and characteristics 128-bit UUIDs are defined in the gatt_uuid128.h just as shown below.
UUID128(uuid_service_otap, 0xE0, 0x1C, 0x4B, 0x5E, 0x1E, 0xEB, 0xA1, 0x5C, 0xEE, 0xF4, 0x5E, 0xBA, 0x50, 0x55, 0xFF, 0x01)
UUID128(uuid_char_otap_control_point, 0xE0, 0x1C, 0x4B, 0x5E, 0x1E, 0xEB, 0xA1, 0x5C, 0xEE, 0xF4, 0x5E, 0xBA, 0x51, 0x55, 0xFF, 0x01)
UUID128(uuid_char_otap_data, 0xE0, 0x1C, 0x4B, 0x5E, 0x1E, 0xEB, 0xA1, 0x5C, 0xEE, 0xF4, 0x5E, 0xBA, 0x52, 0x55, 0xFF, 0x01)
The service is included into the GATT database of the device. It is declared in the gatt_db.h file as shown below.
PRIMARY_SERVICE_UUID128(service_otap, uuid_service_otap)
CHARACTERISTIC_UUID128(char_otap_control_point, uuid_char_otap_control_point, (gGattCharPropWrite_c | gGattCharPropIndicate_c))
VALUE_UUID128_VARLEN(value_otap_control_point, uuid_char_otap_control_point, (gPermissionFlagWritable_c), 16, 16, 0x00)
CCCD(cccd_otap_control_point)
CHARACTERISTIC_UUID128(char_otap_data, uuid_char_otap_data, (gGattCharPropWriteWithoutRsp_c))
VALUE_UUID128_VARLEN(value_otap_data, uuid_char_otap_data, (gPermissionFlagWritable_c), gAttMaxMtu_c - 3, gAttMaxMtu_c - 3, 0x00)
The Bluetooth LE OTAP Control Point characteristic should be large enough for the longest command which can be exchanged between the OTAP Server and The OTAP Client.
The Bluetooth LE OTAP Data characteristic should be large enough for the longest data chunk command the OTAP Client expects from the OTAP Server to be sent via ATT. The maximum length of the OTAP Data Characteristic value is ATT_MTU- 3. 1 byte is used for the ATT OpCode and 2 bytes are used for the Attribute Handle when performing a Write Without Response, the only operation permitted for this characteristic value.
Parent topic:Bluetooth Low Energy OTAP service-profile
OTAP server and OTAP client interactions
The OTAP Server application scans for devices advertising the OTAP Service. When it finds one it connects to that device and notifies it of the available image files or waits for requests regarding available image files. The behavior is specific to each application which needs the OTAP functionality. The Bluetooth LE OTAP Protocol described below details how to do this.
After an OTAP Server (GAP Central, GATT Client) connects to an OTAP Client (GAP Peripheral, GATT Server) it scans the device database and identifies the handles of the OTAP Control Point and OTAP Data characteristics and their descriptors. Then it writes the CCC Descriptor of the OTAP Control point to allow the OTAP Client to send it commands via ATT Indications. It can send commands to the OTAP Client by using ATT Write Commands to the OTAP Control Point characteristic.
After the connection is established, if the OTAP Client wants to use the L2CAP CoC transfer method it must register a L2CAP PSM with the OTAP Server.
The OTAP Client only starts any image information request or image transfer request procedures only after the OTAP Server writes the OTAP Control Point CCCD to ensure there is bidirectional communication between the devices.
Parent topic:Bluetooth Low Energy OTAP service-profile
Parent topic:Over the Air Programming (OTAP)