Embedded Design Handbook

ID 683689
Date 8/28/2023
Public
Document Table of Contents

5.3.4.3.2. Boot Image Header Format

Each boot image includes a header at offset 0x0. The example boot copier uses the header information attached to each boot image to extract information about the image and to make various decisions during the boot process. The make_flash_image_script.sh command-shell script automatically adds the header information to any boot image. The following table lists the information contained in the boot image header.

Table 45.   Example Boot Image Header Format

Field

Size

Description

Location

Signature

32 bits

The signature used to locate the header in flash memory.

Defined in make_flash_image_script.sh. The default boot signature is 0xa5a5a5a5.

Version

32 bits

A binary encoded version identifier for the application.

Defined in make_flash_image_script.sh.

Timestamp

32 bits

The time the header was created. Uses the standard C time integer value, seconds since JAN 01, 1970.

Generated by make_flash_image_script.sh.

Data length

32 bits

The length of the application data contained in the boot, in bytes.

Generated by make_flash_image_script.sh.

Data CRC

32 bits

The CRC32 value for the entire application data

Generated by make_flash_image_script.sh.

Unused 0

32 bits

Unspecified purpose.

Defined in make_flash_image_script.sh.

Unused 1

32 bits

Unspecified purpose.

Defined in make_flash_image_script.sh.

Header CRC

32 bits

The CRC32 value for the header data.

Generated by make_flash_image_script.sh.