# Serial flasher

## Overview

Serial flasher component provides portable library for flashing Espressif SoCs (`ESP32`, `ESP32-S2`, `ESP8266`) from other host microcontroller. Espressif SoCs are normally programmed via serial interface (UART). Port layer for given host microcontroller has to be implemented, if not available. Details can be found in section below.

## Supporting new host target

In order to support new target, following function has to be implemented by user:

* loader_port_serial_read()
* loader_port_serial_write()
* loader_port_enter_bootloader()
* loader_port_delay_ms()
* loader_port_start_timer()
* loader_port_remaining_time()

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

* loader_port_change_baudrate()
* loader_port_reset_target()
* loader_port_debug_print()

Prototypes of all function mentioned above can be found in [serial_io.h](include/serial_io.h).
Please refer to ports in `port` directory. Currently, only ports for [ESP32 port](port/esp32_port.c) and [STM32 port](port/stm32_port.c) are available.

## Configuration

Apart from writing port (if not available), user can enable flash integrity check functionality by setting MD5_ENABLED option. If enabled, serial flasher is capable of verify flash integrity after writing to memory.

Configuration can be passed to `cmake` via command line:

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

Note: in case, no compile definitions are provided, ESP32 is set as target and MD5 check is enabled by default. As ROM bootloader of ESP8266 does not support MD5_CHECK, `-DMD5_ENABLED=0` has to be passed to command line.

### STM32 support

STM32 port make use of STM32 HAL libraries, that does not come with CMake support. In order to compile the project, `stm32-cmake` (`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 definition to command line, such as:

```
cmake -DTOOLCHAIN_PREFIX="/path_to_toolchain" -DSTM32Cube_DIR="path_to_stm32Cube" -DSTM32_CHIP="STM32F407VG" -DPORT="STM32" .. && cmake --build .
```
Alternatively, set those variables in top level `cmake` directory:

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

## Licence

Code is distributed under Apache 2.0 license.

## Known limitations

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