esp-serial-flasher

esp-serial-flasher is a portable C library for flashing or loading apps to RAM of Espressif SoCs from other host microcontrollers.

Using the library

Espressif SoCs are normally programmed via serial interface (UART). The port layer for the given host microcontroller has to be implemented if not available. Details can be found in section below.

Supported host microcontrollers:

• STM32
• Raspberry Pi SBC
• ESP32
• Any MCU running Zephyr OS

Supported target microcontrollers:

• ESP32
• ESP8266
• ESP32-S2
• ESP32-S3
• ESP32-C3
• ESP32-C2
• ESP32-H2

Supported hardware interfaces:

• UART
• SPI (only for RAM download, experimental)

For example usage check the examples directory.

Supporting a new host target

In order to support a new target, following functions have to be implemented by user:

• loader_port_read()
• loader_port_write()
• loader_port_enter_bootloader()
• loader_port_delay_ms()
• loader_port_start_timer()
• loader_port_remaining_time()

For the SPI interface ports

• loader_port_spi_set_cs() needs to be implemented as well.

The following functions are part of the io.h header for convenience, however, the user does not have to strictly follow function signatures, as there are not called directly from library.

• loader_port_change_transmission_rate()
• loader_port_reset_target()
• loader_port_debug_print()

Prototypes of all functions mentioned above can be found in io.h.

Configuration

These are the configuration toggles available to the user:

• SERIAL_FLASHER_INTERFACE_UART/SERIAL_FLASHER_INTERFACE_SPI

This defines the hardware interface to use. SPI interface only supports RAM download mode and is in experimental stage and can undergo changes.

Default: SERIAL_FLASHER_INTERFACE_UART

• MD5_ENABLED

If enabled, esp-serial-flasher is capable of verifying flash integrity after writing to flash.

Default: Enabled

Warning: As ROM bootloader of the ESP8266 does not support MD5_CHECK, this option has to be disabled!

• SERIAL_FLASHER_RESET_HOLD_TIME_MS

This is the time for which the reset pin is asserted when doing a hard reset in milliseconds.

Default: 100

• SERIAL_FLASHER_BOOT_HOLD_TIME_MS

This is the time for which the boot pin is asserted when doing a hard reset in milliseconds.

Default: 50

Configuration can be passed to cmake via command line:

cmake -DMD5_ENABLED=1 .. && cmake --build .

STM32 support

The STM32 port makes use of STM32 HAL libraries, and these do not come with CMake support. In order to compile the project, stm32-cmake (a CMake support package) has to be pulled as submodule.

git clone --recursive https://github.com/espressif/esp-serial-flasher.git

If you have cloned this repository without the --recursive flag, you can initialize the submodule using the following command:

git submodule update --init

In addition to configuration parameters mentioned above, following definitions has to be set:

• TOOLCHAIN_PREFIX: path to arm toolchain (i.e /home/user/gcc-arm-none-eabi-9-2019-q4-major)
• STM32Cube_DIR: path to STM32 Cube libraries (i.e /home/user/STM32Cube/Repository/STM32Cube_FW_F4_V1.25.0)
• STM32_CHIP: name of STM32 for which project should be compiled (i.e STM32F407VG)
• PORT: STM32

This can be achieved by passing definitions to the command line, such as:

cmake -DTOOLCHAIN_PREFIX="/path_to_toolchain" -DSTM32Cube_DIR="path_to_stm32Cube" -DSTM32_CHIP="STM32F407VG" -DPORT="STM32" .. && cmake --build .

Alternatively, those variables can be set in the top level cmake directory:

set(TOOLCHAIN_PREFIX    path_to_toolchain)
set(STM32Cube_DIR       path_to_stm32_HAL)
set(STM32_CHIP          STM32F407VG)
set(PORT                STM32)

Zephyr support

The Zephyr port is ready to be integrated into Zephyr apps as a Zephyr module. In the manifest file (west.yml), add:

    - name: esp-flasher
      url: https://github.com/espressif/esp-serial-flasher
      revision: master
      path: modules/lib/esp_flasher

And add

CONFIG_ESP_SERIAL_FLASHER=y
CONFIG_CONSOLE_GETCHAR=y
CONFIG_SERIAL_FLASHER_MD5_ENABLED=y

to the project configuration prj.conf.

For the C/C++ source code, the example code provided in examples/zephyr_example can be used as a starting point.

Licence

Code is distributed under Apache 2.0 license.

Known limitations

Size of new binary image has to be known before flashing.