STM32F411CEU6 (Black Pill) DFU Bootloader + Application

This project demonstrates a USB DFU (Device Firmware Upgrade) bootloader with a sample user application for the STM32F411CEU6 microcontroller, such as the Black Pill board.

It allows firmware upgrades over USB without needing ST-Link or toggling BOOT0 — perfect for production or remote updates.

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🧭 How to Enter DFU Bootloader Mode

✅ Method (No BOOT0 Needed)

To trigger DFU mode on boot:

• Step 1: Press and hold the Boot Button (connected to PA0) available on the board.
• Step 2: Power on the board or press the reset button (while still holding the Boot Button).
• Step 3: After ~0.5 seconds, release the Boot Button.

🔄 The LED on PC13 will blink rapidly (100ms interval) to indicate DFU mode is active.

❌ If no valid application is found, the LED on PC13 will double-blink every 1.5 seconds to indicate the application is not found.

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🔌 Connection Methods

• USB DFU Mode:
  Connect a USB data cable to the board's USB Micro or Type-C port.

• No UART/Serial Needed:
  This bootloader does not require BOOT0 or UART (PA9/PA10) usage.

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🚀 Application Details (Important)

The user application is flashed to 0x08008000 onward.

📦 Linker Script (application.ld) — ⚠️ Do Not Ignore This

MEMORY
{
  RAM      (xrw) : ORIGIN = 0x20000000, LENGTH = 128K
  FLASH    (rx)  : ORIGIN = 0x08008000, LENGTH = 480K
}

⚠️ Important: This ensures the application does not overwrite the bootloader and has access to the full RAM.

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💾 Flashing Firmware

Use one of the following tools that support USB DFU:

• ✅ STM32CubeProgrammer
• ✅ dfu-util (Linux/macOS/WSL)

Flash your firmware binary (.bin or .hex) starting at address:

0x08008000

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❎ Below is the Bootloader Internal Details (Can Be Ignored)

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🧠 Bootloader Details

The bootloader is flashed to the first 32KB of flash (0x08000000–0x08007FFF).

📦 Linker Script (bootloader.ld)

MEMORY
{
  BOOTFLAG (xrw)  : ORIGIN = 0x20000000 , LENGTH = 0x8           /* 8 bytes for boot_flag */
  RAM      (xrw)  : ORIGIN = 0x20000008 , LENGTH = 128K - 0x8
  FLASH    (rx)   : ORIGIN = 0x08000000 , LENGTH = 32K
}

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📁 Project Structure

stm32f411ceu6_dfu_bootloader_applicationer/
├── stm32_bootloader     # USB DFU Bootloader (starts at 0x08000000)
└── stm32_application    # User application (starts at 0x08008000)

Each project includes STM32CubeMX .ioc, Makefile, USB stack, HAL drivers, and build folders.

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🛠️ Build & Flash

You can build, flash via DFU, and open a serial monitor using the included helper Makefile in each folder.

🧰 Example Helper Makefile

# Build target (requires sub-make in ./Debug)
make all

# Flash using dfu-util (must have sudo or permissions)
make flash

# Open serial monitor (uses miniterm from pyserial)
make serial

# Clean build
make clean

Update this line in the Makefile to match your serial device:

SERIAL := /dev/ttyUSB0

💡 Tip: Make sure dfu-util and pyserial are installed:

sudo apt install dfu-util
pip install pyserial

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✅ How It Works

🔌 1. Power-Up / Reset

• Bootloader checks a boot flag in RAM to decide whether to enter DFU or jump to the application.

💻 2. DFU Mode (Firmware Update)

• If a DFU request is detected (via PA0 or host), bootloader enters USB DFU mode.
• While in DFU mode, LED (PC13) blinks at 100ms interval.

🚀 3. Application Launch

• If no DFU request is detected and a valid application is found at 0x08008000, it jumps to the app.
• If the application is not valid, LED (PC13) shows a double-blink every 1.5 seconds.

🛠️ You can customize this logic in main.c — GPIO, UART, button triggers, etc.

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📦 Requirements

• STM32F411CEU6 (e.g., Black Pill board)
• USB cable
• ST-Link (for initial bootloader flash only)
• dfu-util
• Python 3 + pyserial

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📄 License

This project is licensed under the MIT License. You're free to use, modify, and distribute.

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💬 Need Help?

Open issues or discussions on the GitHub repository:
👉 https://github.com/riteshtheone/stm32f411ceu6_dfu_bootloader_application

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