Create README.md

Author: riteshtheone

README.md

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+# STM32F411CEU6 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.
+
+---
+
+## 📁 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.
+
+---
+
+## 🧠 Bootloader Details
+
+The bootloader is flashed to the **first 32KB of flash** (`0x08000000–0x08007FFF`).
+
+### 📦 Linker script (bootloader `.ld`)
+```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
+}
+```
+
+- **BOOTFLAG** is an 8-byte RAM section used to pass DFU/app boot info.
+- **FLASH** is limited to the first 32KB for the bootloader.
+
+---
+
+## 🚀 Application Details
+
+The user application is flashed to **0x08008000** onward.
+
+### 📦 Linker script (application `.ld`)
+```ld
+MEMORY
+{
+  RAM      (xrw) : ORIGIN = 0x20000000, LENGTH = 128K
+  FLASH    (rx)  : ORIGIN = 0x08008000, LENGTH = 480K
+}
+```
+
+- This ensures it does **not overwrite** the bootloader.
+- RAM is shared fully (application does not touch boot flag logic).
+
+---
+
+## 🛠️ Build & Flash
+
+You can build, flash via DFU, and open a serial monitor using the included helper `Makefile` in each folder.
+
+### Example helper `Makefile`
+```make
+# 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:
+```make
+SERIAL := /dev/ttyUSB0
+```
+
+> Make sure `dfu-util` and `pyserial` are installed:
+```bash
+sudo apt install dfu-util
+pip install pyserial
+```
+
+---
+
+## ✅ How It Works
+
+1. On power-up/reset:
+   - Bootloader checks a boot flag in RAM to decide whether to enter DFU or jump to the app.
+2. On DFU request (from host or condition):
+   - Bootloader stays in DFU mode and exposes the USB firmware update interface.
+3. Otherwise:
+   - Jumps to user app at `0x08008000`.
+
+You can modify this logic in `main.c` of the bootloader to customize trigger methods (e.g. GPIO pin, UART command, button, etc.).
+
+---
+
+## 📦 Requirements
+
+- STM32F411CEU6 (e.g., Black Pill board)
+- USB cable
+- ST-Link (for first bootloader flash only)
+- `dfu-util`
+- Python 3 + pyserial
+
+---
+
+## 📄 License
+
+This project is MIT licensed. You're free to use, modify, and distribute.
+
+---
+
+## 💬 Need Help?
+
+Feel free to open issues or discussions on the GitHub repository:
+👉 [https://github.com/riteshtheone/stm32f411ceu6_dfu_bootloader_application](https://github.com/riteshtheone/stm32f411ceu6_dfu_bootloader_application)