Bluetooth Low Energy OTAP header

The format and fields of the Bluetooth Low Energy OTAP Header are summarized in the table below.

|Octets|Data Types|Field Name|Mandatory/Optional| |4|Unsigned 32-bit integer|Upgrade File Identifier|M| |2|Unsigned 16-bit integer|Header Version|M| |2|Unsigned 16-bit integer|Header Length|M| |2|Unsigned 16-bit integer|Header Field Control|M| |2|Unsigned 16-bit integer|Company Identifier|M| |2|Unsigned 16-bit integer|Image ID|M| |8|8 byte array|Image Version|M| |32|Character string|Header String|M| |4|Unsigned 32-bit integer|Total Image File Size

(including header)

|M|

The fields are shown in the order they are placed in memory from the first location to the last.

The total size of the header without the optional fields (if defined by the Header Field Control) is 58 bytes.

All the fields in the header have a little endian format with the exception of the Header String field which is an ASCII character string.

A packed structure type definition for the contents of the Bluetooth LE OTAP Header can be found in the otap_interface.hfile.

Upgrade file identifier

Fixed value 4 byte field used to identify the file as being a Bluetooth LE OTAP Image File. The predefined value is “0x0B1EF11E”.

Parent topic:Bluetooth Low Energy OTAP header

Header version

This 2 byte field contains the major and minor version number. The high byte contains the major version and the low byte contains the minor version. The current value is “0x0100” with the major version “01” and the minor version “00”. A change to the minor version means the OTA upgrade file format is still backward compatible, while a change to the major version suggests incompatibility.

Parent topic:Bluetooth Low Energy OTAP header

Header length

Length of all the fields in the header including the Upgrade File Identifier field, Header Length field and all the optional fields. The value insulates existing software against new fields that may be added to the header. If new header fields added are not compatible with current running software, the implementations should process all fields they understand and then skip over any remaining bytes in the header to process the image or CRC sub-element. The value of the Header Length field depends on the value of the Header Field Control field, which dictates which optional header fields are included.

Parent topic:Bluetooth Low Energy OTAP header

Header field control

This is a 2-byte bit mask that specifies the optional fields present in the OTAP Header.

In case no optional fields are defined, this whole field is reserved and should be set to “0x0000”.

Parent topic:Bluetooth Low Energy OTAP header

Company identifier

This is the company identifier assigned by the Bluetooth SIG. The Company Identifier used for the OTAP demo applications is “0x01FF”.

Parent topic:Bluetooth Low Energy OTAP header

Image ID

This is a unique short identifier for the image file. It is used to request parts of an image file. This number should be unique for all images available on a Bluetooth LE OTAP Server.

The value 0x0000 is reserved for the current running image.
The value 0xFFFF is reserved as a “no image available” code for New Image Info Response commands.

This field value must be used in the ImageID field in the New Image Notification and New Image Info Response commands.

Parent topic:Bluetooth Low Energy OTAP header

Image version

This is the full identifier of the image file. It should allow a Bluetooth LE OTAP Client to identify the target hardware, stack version, image file build version, and other parameters if necessary. The recommended format of this field (which is used by the OTAP Demo applications) is shown below but an end device manufacturer could choose different format. The subfields are shown in the order they are placed in memory from the first location to the last. Each subfield has a little-endian format, if applicable. Refer Table 1

Subfield	Size (bytes)	Format	Description
Build Version	3	uint8[]	Image build version.
Stack Version	1	uint8	0x41 for example for Bluetooth Low Energy Stack version 4.1.
Hardware ID	3	uint8[]	Unique hardware identifier.
End Manufacturer Id	1	uint8	ID of the hardware–specific to the end manufacturer

This field value must be used in the ImageVersion field in the New Image Notification and New Image Info Response commands.

Parent topic:Bluetooth Low Energy OTAP header

Header string

This is a manufacturer-specific string that may be used to store other necessary information as seen fit by each manufacturer. The idea is to have a human readable string that can prove helpful during the development cycle. The string is defined to occupy 32 bytes of space in the OTAP Header. The default string used for the Bluetooth LE OTAP demo application is “BLE OTAP Demo Image File”.

Parent topic:Bluetooth Low Energy OTAP header

Total image file size

The value represents the total image size in bytes. This is the total of data in bytes that is transferred over-the-air from the server to the client. In most cases, the total image size of an OTAP upgrade image file is the sum of the sizes of the OTAP Header and all the other sub-elements on the file. If the image contains any integrity and/or source identity verification fields then the Total Image File Size also includes the sizes of these fields.

Parent topic:Bluetooth Low Energy OTAP header

Parent topic:Bluetooth Low Energy OTAP image file format