esp-idf/docs/en/api-reference/system/bootloader_image_format.rst

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Bootloader Image Format
=======================
The bootloader image consists of the same structures as the application image, see :ref:`Application Image Structures <app-image-structures>`. The only difference is in the :ref:`Bootloader Description <image-format-bootloader-description>` structure.
To get information about the bootloader image, please run the following command:
.. code-block::
esptool.py --chip {IDF_TARGET_PATH_NAME} image_info build/bootloader/bootloader.bin --version 2
.. code-block::
File size: 26576 (bytes)
ESP32 image header
==================
Image version: 1
Entry point: 0x40080658
Segments: 4
Flash size: 2MB
Flash freq: 40m
Flash mode: DIO
ESP32 extended image header
===========================
WP pin: 0xee
Flash pins drive settings: clk_drv: 0x0, q_drv: 0x0, d_drv: 0x0, cs0_drv: 0x0, hd_drv: 0x0, wp_drv: 0x0
Chip ID: 0
Minimal chip revision: v0.0, (legacy min_rev = 0)
Maximal chip revision: v3.99
Segments information
====================
Segment Length Load addr File offs Memory types
------- ------- ---------- ---------- ------------
1 0x01bb0 0x3fff0030 0x00000018 BYTE_ACCESSIBLE, DRAM, DIRAM_DRAM
2 0x03c90 0x40078000 0x00001bd0 CACHE_APP
3 0x00004 0x40080400 0x00005868 IRAM
4 0x00f2c 0x40080404 0x00005874 IRAM
ESP32 image footer
==================
Checksum: 0x65 (valid)
Validation hash: 6f31a7f8512f26f6bce7c3b270f93bf6cf1ee4602c322998ca8ce27433527e92 (valid)
Bootloader information
======================
Bootloader version: 1
ESP-IDF: v5.1-dev-4304-gcb51a3b-dirty
Compile time: Mar 30 2023 19:14:17
.. _image-format-bootloader-description:
Bootloader Description
----------------------
The ``DRAM0`` segment of the bootloader binary starts with the :cpp:type:`esp_bootloader_desc_t` structure which carries specific fields describing the bootloader. This structure is located at a fixed offset = sizeof(:cpp:type:`esp_image_header_t`) + sizeof(:cpp:type:`esp_image_segment_header_t`).
* ``magic_byte`` - the magic byte for the esp_bootloader_desc structure.
* ``reserved`` - reserved for the future IDF use.
* ``version`` - bootloader version, see :ref:`CONFIG_BOOTLOADER_PROJECT_VER`
* ``idf_ver`` - ESP-IDF version. ``*``
* ``date`` and ``time`` - compile date and time.
* ``reserved2`` - reserved for the future IDF use.
``*`` - The maximum length is 32 characters, including null-termination character.
To get the :cpp:type:`esp_bootloader_desc_t` structure from the running bootloader, use :cpp:func:`esp_bootloader_get_description`.
To get the :cpp:type:`esp_bootloader_desc_t` structure from a running application, use :cpp:func:`esp_ota_get_bootloader_description`.
API Reference
-------------
.. include-build-file:: inc/esp_bootloader_desc.inc