Prebuilt ESP32 second-stage bootloaders

These are the ESP-IDF second-stage bootloaders, flashed at offset 0x0. The ROM loads this bootloader, which then reads the partition table (0x8000) and loads the Betaflight app from the factory partition (0x10000).

By default the build compiles the bootloader from source (ESP_BOOTLOADER_FROM_SOURCE=yes, see ../mk/tools.mk); the binaries here are the opt-out fallback used when ESP_BOOTLOADER_FROM_SOURCE=no. The IDF bootloader is a self-contained sub-project (its own linker script, startup and ~dozens of sources, driven by CMake/Kconfig), so a prebuilt blob is a handy alternative when you don't want to build it. The bootloader is chip-specific but otherwise stable, and esptool patches the flash mode/size/freq into its header at flash time, so one binary per chip is sufficient.

The build (make ESP32S3) generates the partition table from ../partitions.csv and merges bootloader + partition table + app into the single bootable .bin (via a transient *_tmp.bin app image that is then deleted), flashable in one step at 0x0.

Provenance / how to regenerate

Built with ESP-IDF v5.4 (the lib/modules/esp-idf submodule) for the chip, default bootloader config, flash mode DIO:

idf.py --preview set-target esp32s3
idf.py bootloader
# -> build/bootloader/bootloader.bin