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48 lines
1.9 KiB
Markdown
48 lines
1.9 KiB
Markdown
# Custom bootloader examples
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The following directory contains two examples presenting the different ways
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we provide in order to override the second stage bootloader or complete it
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with few hooks.
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## Extending the bootloader
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In both cases, a project can define custom bootloader components by creating
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them within a directory called `bootloader_components`.
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Naming one of them `main` would let the compiler entirely override the
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2nd stage bootloader with the implementation provided.
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The bootloader components containing the hooks can have any name, as long
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as it is part of `bootloader_components`, it will be taken into account
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in the build.
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## Hooks vs overriding the bootloader
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In brief, using hooks will let the application add code to the bootloader.
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They cannot replace the code that is already executed within bootloader.
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Two hooks are available at the moment, the first one is called before the
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initialization, and the second one is performed after the bootloader
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initialization, before choosing and loading any partition. The
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signature for these hooks can be found in `bootloader_hooks.h` file in
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`components/bootloader/subproject/main/`.
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On the other hand, overriding the bootloader offers the possibility to
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totally or partially re-write it, in order to include, remove or modify
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parts of it. Thanks to this, it will be fully customizable.
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This shall only be used if heavy changes are required and they cannot
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be done with hooks or within an application.
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## Component code supported in bootloader
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Links to the resources of component APIs supporting bootloader code are
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listed below.
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### NVS Flash
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NVS flash component provides limited, read-only API. It is documented in
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[NVS Flash Component for Bootloader](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/storage/nvs_bootloader.html)
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Examples of it's use are located in `examples/storage/nvs_bootloader`
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