This is the source of the software flasher stub.

esptool.py loads the flasher stub into memory and executes it to:

• Add features that the ESP8266 & ESP32 bootloader ROMs do not have.

• Add features to the ESP8266 bootloader ROM which are only in the ESP32 ROM.

• Improve flashing performance over the ROM bootloaders.

• Work around bugs in the ESP8266 ROM bootloader.

Thanks to Cesanta who provided the original ESP8266 stub loader upon which this loader is based.

To Use

The stub loader is already automatically integrated into esptool.py. You don’t need to do anything special to use it.

To Build

If you want to build the stub to test modifications or updates, here’s how:

• You will need both an ESP8266 gcc toolchain (xtensa-lx106-elf-) and an ESP32 toolchain (xtensa-esp32-elf-) on your PATH.

• Set the environment variables SDK_PATH to the path to an ESP8266 IoT NON-OS SDK directory (last stub was built with SDK v1.5.1).

• Set the environment variable IDF_PATH to the path to an ESP-IDF directory.

• Set any other environment variables you’d like to override in the Makefile.

• To build type make

To Test

To test the build stub, you can either copy-paste the code from build/stub_flasher_snippet.py into esptool.py manually. Or there are some convenience wrappers to make testing quicker to iterate on:

• Running esptool_test_stub.py is the same as running esptool.py, only it uses the just-compiled stubs from the build directory.

• Running run_tests_with_stub.py is the same as running test/test_esptool.py, only it uses the just-compiled stubs from the build directory.