This sample code demonstrates how to flash an Espressif SoC (target) from another MCU (host) using esp_serial_flasher. In this case, the ESP32 is used as the host MCU. Binaries to be flashed from the host MCU to another Espressif SoC can be found in binaries folder and are converted into C-array during build process.

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

Peripherals are initialized (GPIO for BOOT and EN pins and UART).
UART1 (can be changed) through which new binary will be transfered is initialized.
The host puts the target device into the boot mode and tries to connect by calling esp_loader_connect().
The binary file is opened and its size is acquired, as it has to be known before flashing.
Then esp_loader_flash_start() is called to enter the 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 steps mentioned above, esp_loader_change_transmission_rate() is called after connection is established in order to increase the flashing speed. This does not apply for ESP8266, as its bootloader does not support this command. However, ESP8266 is capable of detecting the baud rate during connection phase and can be changed before calling esp_loader_connect(), if necessary.

Hardware Required

Any supported Espressif SoC board for the target
An ESP32-DevKitC board for the host
One or two USB cables for power supply and programming.

Hardware connection

Table below shows connection between the two devices:

ESP32 (host)	Espressif SoC (target)
IO26	IO0
IO25	RESET
IO4	RX0
IO5	TX0

Build and flash

To run the example, type the following commands:

west init
west update
west build -p -b <supported board>
west flash
west espressif monitor

Note: You can find the supported boards in the boards folder.

(To exit the serial monitor, type ctrl-c.)

For more information, check Zephyr's Getting Started

Configuration

For details about available configuration option, please refer to top level README.md. Compile definitions can be specified in prj.conf file.

Binaries to be flashed are placed in a separate folder (binaries.c) for each possible target and converted to C-array. Without explicitly enabling MD5 check, flash integrity verification is disabled by default.

Example output

Here is the example's console output:

Running ESP Flasher from Zephyr
Connected to target
Transmission rate changed.
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Flash verified
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Flash verified
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Flash verified
********************************************
*** Logs below are print from slave .... ***
********************************************
Hello world!