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