Flashing Bootloader

Integrate into STM32CubeMX project

• Create STM32CubeMX project for your chip
• Configure HSE clocks, enable Serial Wire Debug
• Enable USART1 or USB depending on required flashing interface
• Enable USART1 DMA (TX → Normal Mode, RX → Circular Mode)
• Enable USART1 Global Interrupt
• Configure PC13 → GPIO output (for LED indication)
• Project Manager → Set toolchain to STM32CubeIDE
• Generate code
• Copy contents of STM32_TOOLKIT folder to Src folder of your project

/* USER CODE BEGIN Includes */

#include "examples.h"

/* USER CODE END Includes */

  /* Configure the system clock */
  SystemClock_Config();

  /* USER CODE BEGIN SysInit */

  APP_Boot();   /* <-- HERE */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_USART1_UART_Init();

  /* USER CODE BEGIN 2 */

  APP_Init();   /* <-- HERE */

  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    APP_Loop(); /* <-- and HERE */
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */

Compiling Application

Run from second half of flash

#define ACTIVE_EXAMPLE_NUM 2

#define FILE_1 "01_firmware_uploader.bin"
#define FILE_2 "02_led_control.bin"  /* SELECTED */
#define FILE_3 "03_device_configurator.bin"
#define FILE_4 "04_temperature_monitor.bin"
#define FILE_5 "05_fft_benchmark.bin"

MEMORY
{
  RAM  (xrw) : ORIGIN = 0x20000000, LENGTH = 20K
  FLASH (rx) : ORIGIN = 0x08008000, LENGTH = 32K  /* 0x0000 → 0x8000 */
}

• Uncomment USER_VECT_TAB_ADDRESS
• Set VECT_TAB_OFFSET = 0x8000
• Project → Properties → C/C++ Build → Settings → MCU/MPU Post Build Outputs → Convert to binary file
• Project → Build project (do not Run to avoid flashing with ST-Link)

Preparing Binary

Add CRC32 footer and encrypt using Web UI

• Rename compiled binary from the Debug folder (e.g. ledctrl_1.0.bin)
• Open 00_firmware_prepare.html from the HTML folder in your browser
• Click Select .bin File and choose ledctrl_1.0.bin
• Encrypted binary enc_ledctrl_1.0.bin will be generated and saved to your default downloads location

Firmware layout after processing:
┌── base firmware (STM32CubeIDE output)
│
├── ↓↓↓  Footer appended at end
│
├── version string (N bytes)
├── version string length N (1 byte)
├── CRC32 (4 bytes, little-endian)
├── 0x55 0x55 0x55 0x55
└── 0xFF ... (empty space)

Flashing Application

Upload firmware via Web UI

• Open 01_firmware_uploader.html in your browser
• Click Upload Firmware button
• Select enc_ledctrl_1.0.bin
• After update completes, open 02_led_control.html to control LED from the browser

USB Support

Flash over USB using CDC

• STM32CubeIDE → Close Project
• Open the project in STM32CubeMX
• Enable the USB peripheral
• Enable the Communication Device Class (CDC) middleware
• Generate code, open project in STM32CubeIDE
• For STM32F103C8T6, set compiler optimization to Optimize for size (-Os) to fit within flash
• In examples.h, set ACTIVE_EXAMPLE_NUM to 1 to compile the firmware uploader example
• Replace UART read/write calls with USB equivalents (e.g. USB_ReadNoWait(cmd))
• No need to change prefix of COM_Init()
• In system_stm32fxxxx.c, comment out USER_VECT_TAB_ADDRESS

/* Memories definition (STM32F103C8T6) */
MEMORY
{
  RAM  (xrw) : ORIGIN = 0x20000000, LENGTH = 20K

  FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 32K  /* <-- when compiling as application */
  /* FLASH (rx) : ORIGIN = 0x8008000, LENGTH = 32K */  /* <-- when compiling as bootloader */

}

Configuring Encryption

Set a secure AES key for production

/* In flash_helper.c: */
uint8_t key[16] = {
  1,2,3,4,5,6,7,8,
  9,10,11,12,13,14,15,16
};

/* In 00_firmware_prepare.html: */
// AES Encryption key
const key = [
  1, 2, 3, 4, 5, 6, 7, 8,
  9, 10, 11, 12, 13, 14, 15, 16
];

Communication Protocol

How the bootloader talks to the host