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esp-idf/docs/en/api-reference/system/bootloader_image_format.rst
2025-09-30 15:28:55 +02:00

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Bootloader Image Format
=======================
:link_to_translation:`zh_CN:[中文]`
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:`image-format-bootloader-description` structure.
To get information about the bootloader image, please run the following command:
.. code-block::
esptool --chip {IDF_TARGET_PATH_NAME} image-info ./build/bootloader/bootloader.bin
The resultant output will resemble the following:
.. code-block::
esptool v5.0.2
Image size: 26352 bytes
ESP32 Image Header
==================
Image version: 1
Entry point: 0x40080644
Segments: 3
Flash size: 2MB
Flash freq: 40m
Flash mode: DIO
ESP32 Extended Image Header
===========================
WP pin: 0xee (disabled)
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 (ESP32)
Minimal chip revision: v0.0, (legacy min_rev = 0)
Maximal chip revision: v3.99
Segments Information
====================
Segment Length Load addr File offs Memory types
------- ------- ---------- ---------- ------------
0 0x018e8 0x3fff0030 0x00000018 BYTE_ACCESSIBLE, DRAM, DIRAM_DRAM
1 0x03e58 0x40078000 0x00001908 CACHE_APP
2 0x00f5c 0x40080400 0x00005768 IRAM
ESP32 Image Footer
==================
Checksum: 0x6b (valid)
Validation hash: 09fdc81d436a927b5018e19073a787cd37ffce655f505ad92675edd784419034 (valid)
Bootloader Information
======================
Bootloader version: 1
ESP-IDF: v6.0-dev-1620-g15d7e41a848-dirt
Compile time: Aug 8 2025 16:22:1
.. _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
* ``secure_version``: the secure version used by the bootloader anti-rollback feature, see :ref:`CONFIG_BOOTLOADER_ANTI_ROLLBACK_ENABLE`.
* ``version``: bootloader version, see :ref:`CONFIG_BOOTLOADER_PROJECT_VER`
* ``idf_ver``: ESP-IDF version. [#f1]_
* ``date`` and ``time``: compile date and time
* ``reserved2``: reserved for the future IDF use
.. [#f1] 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