OAD Image Header

All firmware images delivered via OAD are in binary format and contain an image header. The information in the image header is used by the application and BIM to determine the suitability of an image for download or loading. In order to prevent this information from being calculated multiple times all TI OAD images use a standard image header.

This section explains the various fields within the image header and what they mean.

TI provides a tool to generate an OAD ready image, it is called OAD Image Tool. By default, this tool runs as a post-build step of all OAD enabled projects.

OAD Image Header Overview

The OAD image header is made up of two parts:

  • The core image header which is fixed and mandatory for all OAD images
  • The image segments which are optional and used to describe specific types of images

The OAD image header is composed of a core header and segments. The core header is required and common to all OAD image headers. The image segments are optional and may be different for a given OAD use case (i.e. on-chip vs off-chip OAD).

The image below illustrates the makeup of an image header, and compares two types. When added to an image by the OAD Image Tool the OAD core header and segments are packed together sequentially.



In general it is not necessary for the customer or user to manually add or modify segments. The segments should be populated and packed out of the box by the TI oad_image_tool.

OAD Core Image Header

The core header contains the essential information required for all types of OAD across all supported wireless stacks. The core header must be present as the BIM relies heavily on it to boot and OAD image.

Table 6. below shows a description of the core image header.

Table 6. Description of the core image header.
Field Size (in bytes) Description
OAD Image Identification Value 8 Unique number to identify the start of an OAD image
CRC 4 Cyclic Redundancy Check
BIM Version 1 Version required to support image format
Image Header Version 1 Version of image header contained in image
Wireless Technology 2 Type of connectivity used in image
Image Information 4 Image information bytes
Image Validation 4 Check if image is valid to run
Image Length 4 The total length of the image including header
Program Entry Address 4 Application startup entry address
Image Software Version 4 Software version of the image
Image End Address 4 End address of the image
Header Length 2 Total length of the image header

The core header is defined in oad_image_header.h in the struct imgFixedHdr_t.

Each entry from Table 6. are described in the following sections.

OAD Image Identification Value

The OAD Image Identification Value for the CC26x2 is set based on the DeviceFamily_* defined that is provided by the SDK. The value is using the the OAD_IMG_ID_VAL define. Note the protocol specific implementation OAD should check that the OAD_IMG_ID_VAL field matches between the image currently resident on the device and the incoming image.

The OAD Image Identification Value serves two purposes:

  • Provides the application a quick way to identify if it is receiving the correct image.
  • Provides a means for the BIM to find the flash page containing the start of OAD image for on-chip OAD


It is recommended that the customer customize the image identification field to uniquely identify their product.


The cyclic redundancy check (CRC) is a means to check the integrity of an image. This must be done in two steps. First the CRC must be calculated when the image is generated from the toolchain (by the OAD Image Tool), this will be stored in the CRC field within the image header.

Later, once the target has received the OAD image, CRC will be recalculated to determine if the image has been corrupted during transfer.

If the CRC is equivalent before and after the OAD, the target can assume that the image was not corrupted while sending over the air.

A CRC-32 algorithm is used to calculate the CRC. This algorithm results in a 1 in 232 chance of collision. This allows for a 99.9999% error detection rate. In addition to this CRC, transfers through the protocol transport are also protected by a CRC. So the risk of an undetected data corruption is reduced even further.

BIM Version

The BIM Version byte is used to determine whether or not the image is compatible with the version of BIM that is running on the device.

Image Header Version

The image header Version byte is used to determine whether or image contains image header that is compatible with the current version of the application and BIM.

Wireless Technology

The Wireless Technology field in the image header describes what technology is used in the image to be downloaded. Multiple technologies can be selected here if the device used supports multiple technologies. These fields are added for future expansion. Bits are set to 1 by default. To select the Wireless Technology field, set the appropriate bit(s) to 0.

Bit Number Type
0 Bluetooth Low Energy
1 IEEE 802.15.4 (Sub 1GHz)
2 IEEE 802.15.4 (2.4GHz)
3 Zigbee
5 Thread
6 Easy Link
7-15 Reserved

Image Information

The Image Information provides details about the OAD image status and type. The format is as follows:

Byte Number Item Description
0 Image Copy Status
0xFF: Default status, no action needed
0xFE: Image to be copied to on-chip flash at location indicated in the image header
0xFC: Image copied
1 CRC Status
0xFC: CRC Invalid
0xFE: CRC Valid
0xFF: CRC Not Calculated Yet
2 Image Type
Device Images (0x00-0x15)
0x00: Persistent application (for On-chip OAD)
0x01: Application
0x02: Stack
0x03: Application & Stack Merged
0x04: Network Processor
0x05: Factory Image
0x06: BIM
0x07: App & Stack Combined (App/Stack_Library)

0x10-0x1F: User data
0x20-0x3F: Host Processor Images
0x40-0xFF: Reserved
3 Image Number
Image number if more than one type is stored
0xFF: Default
0x00-0xFE: Image number


Image type 0x03 (Application & Stack Merged) is different from 0x07 (App & Stack Combined). Image type 0x03 refers to the case where app and stack are build as separate split images and combined using a hex merging tool. Image type 0x07 refers to a app and stack being built as a single executable.


BIM will not try to interpret user data/application (anything with image type > 0x10).

Image Validation

The image validation field is currently not used and is reserved for future use.

Image Length

The Image Length field is the total length of the executable portion of the image in bytes. Image length is calculated by the OAD image tool using the following equation:

\textrm{imgLen} = \textrm{imgEndAddr} - \textrm{imgStAddr} + 1

Note that the tool will pad the image length to be word aligned, updating the length if needed.


  • imgEndAddr: Last used address in flash
  • imgStAddr: The first address used in flash (starts at _imgHdr.imgID)

Program Entry Address

The Program Entry Address is a pointer to the application interrupt vector table or application program entry address. This provides flexibility so that if the program entry address changes between images, BIM will still be able to use this field to run the application.

Software version

The Software Version field is used to keep track of the application and stack revision contained in the image. This field follows the following format:

These values are assigned as shown in the table below.

Byte Number Description
3-2 Stack version
1-0 Application version

For example an image with app version 1.0 and stack version 3.0 would be designated as: {'3', '0', '1', '0'}. This field is to be set by the user in their header implementation. (i.e. oad_image_header*.c)

Image End Address

The Image End Address is the last address in flash occupied by the image.

Header Length

The Header Length is the length of the core portion of the header. This is up to and including the rfu2 field in the structure defined in oad_image_header.h.

OAD Image Header segments

The segment structure was designed to make the current OAD implementation flexible and extensible. This makes it possible to expand the image header vector as features are added to the OAD implementation without breaking the existing system.

Table 7. Description of the image header segments.
Field Size (in bytes) Description
Boundary Information 24 Contains information about RAM and Flash boundaries
Contiguous Image Information 12 Contains information about image to be downloaded


The current implementation only supports images of contiguous type, thus this segment is required.

The boundary segment is optional and only required for split image types.

Segment Header

Each segment has a common header structure. This is useful when parsing an image for segments. The header structure is used by all segments. The common header will be documented below so it does not have to be repeated for each segment type.

Field Size (in bytes) Description
Segment type = X 1 Segment header op-code
Wireless technology 2 Same options as in the main wireless technology table above. Only one bit may be set here.
Reserved 1 Default is set to 0xFF
Payload length 4 The length of the segment in bytes

Segment Type

The segment type field is a one byte op-code that is useful in identifying the segment type.

Wireless Technology

This is the type of wireless technology that is contained in the segment. Each segment may be built for only one wireless tech, thus only one bit can be set in this field.


This field is currently unused and existing designs should not rely on this field.

Payload Length

The length of the entire segment in bytes.

Boundary Information Segment

The Boundary Information field is intended for split image type OAD (where the application and stack are separate images) and is optional. The boundary segment provides information to BIM on the flash and RAM boundaries of the image and its associated wireless stack image.

This information is formatted in the following way:

Item Size (in bytes) Description
Segment type = 0 1 Tells the BIM that the following fields provide RAM and stack boundary information
Wireless technology 2 Same options as in the main wireless technology table above. Only one bit may be set here.
Reserved 1 Default is set to 0xFF
Payload length 4 The length of the boundary information field in bytes
Stack Entry Address 4 Stack entry address
ICALL_STACK0_ADDR 4 Stack boundary address
RAM_START_ADDR 4 Start address of RAM
RAM_END_ADDR 4 End address of RAM

The boundary segment is defined in oad_image_header.h in the struct boundarySeg_t. See this structure in Doxygen for more information.

Stack Entry Address

This is the entry point to the stack image, required when the app and stack are of split image type.

Stack Boundary Address (ICALL_STACK0_ADDR)

The address of the app/stack boundary. This is the lowest address occupied by the stack.

Lower RAM Boundary (RAM_START_ADDR)

The lower address of the RAM region reserved by the stack image.

Upper RAM Boundary (RAM_END_ADDR)

The upper address of the RAM region reserved by the stack image.

Contiguous Image Information Segment

The Continuous Image Information field provides information about the image to be downloaded during the OAD process. The information is formatted in the following way:

Item Size (in bytes) Description
Segment type = 1 1 Tells the BIM that the following fields provide information about the image payload
Wireless technology 2 Same options as in the main wireless technology table above. Only one bit may be set here.
Reserved 1 Default is set to 0xFF
Image Segment Len 4 The length of the continuous image segment in bytes
Image Start Address 4 Address of executable image data

The contiguous image segment is defined in oad_image_header.h in the struct imgPayloadSeg_t. See this structure in Doxygen for more information.

Image Start Address

The starting address of the contigous image segemnt. The information in this segment will be filled in sequentially from the start address.