This example demonstrates how to flash an Espressif SoC (target) from STM32 MCU (host) using esp_serial_flasher. WeActStudio MiniSTM32H7xx board is used in this example, as STM32H743VIT has FLASH memory large enough to fit all the example binaries to be flashed from the host MCU to the Espressif SoC which can be found in binaries directory and converted into C-arrays during build process. USART1 is dedicated for communication with the Espressif SoC, whereas, USART2 can be used for debug purposes by attaching UART-to-USB bridge.

The following steps are performed in order to re-program targets memory:

Peripherals are initialized.
Host puts slave device into boot mode tries to connect by calling esp_loader_connect().
Then esp_loader_flash_start() is called to enter flashing mode and erase amount of memory to be flashed.
esp_loader_flash_write() function is called repeatedly until the whole binary image is transfered.

Note: In addition to the steps mentioned above, esp_loader_change_transmission_rate() is called after connection is established in order to increase the flashing speed. Bootloader is also capable of detecting the baud rate during connection phase. The baud rate can be changed before calling esp_loader_connect(). However, it is recommended to start at lower speed and then use dedicated command to increase the baud rate. This does not apply for ESP8266, as its bootloader does not support this command, therefore, baud rate can only be changed before connection phase in this case.

Hardware Required

WeActStudio MiniSTM32H7xx board with the STM32H743VIT chip.
A development board with the ESP32 SoC (e.g. ESP-WROVER-KIT, ESP32-DevKitC, etc.).
One or two USB cables for power supply and programming.

Hardware connection

Table below shows connection between STM32 and ESP32.

STM32 (host)	ESP32 (slave)
PB12	IO0
PB13	RST
PA2	RX0
PA3	TX0

Optionally, UART-to-USB bridge can be connected to PA9(TX) and PA10 (RX) for the debug purposes (same pins can be used to flash STM32 in bootloader).

Build and flash

To compile the example:

Create and navigate to build directory:

mkdir build && cd build

Run cmake (with appropriate parameters) and build:

cmake -DSTM32_TOOLCHAIN_PATH="path_to_toolchain" -DSTM32_CUBE_H7_PATH="path_to_cube_libraries" .. && cmake --build .

Binaries to be flashed are placed in the separate folder (binaries.c) for each possible target and converted to C-array. Flash integrity verification is enabled by default.

For more details regarding to esp_serial_flasher configuration and STM32 support, please refer to the top level README.md.

Note: CMake 3.16 or later is required.