SimpleBoot

A robust bootloader implementation for STM32F103C8T6 microcontroller using Y-modem protocol for firmware updates over UART. Can be used with other STM32F1x microcontrollers or STM32F4x microcontrollers.

Features

• Y-Modem Protocol Support: Full implementation of Y-modem file transfer protocol
• UART Communication: 115200 baud rate communication for firmware updates
• Flash Management: Automatic flash erase and programming with verification
• Application Validation: Checks for valid application before jumping
• Multiple Entry Methods: Button press, magic number, or no valid application
• CRC32 Verification: Ensures firmware integrity
• LED Indicators: Visual feedback during operation
• Compact Design: Fits in 16KB bootloader space

Hardware Requirements

• MCU: STM32F103C8T6 (Blue Pill board or similar)
• UART: USART1 (PB6-TX, PB7-RX)
• LED: Connected to PA1 (optional)
• Button: Connected to PC13 with pull-up (optional)
• Crystal: 8MHz external crystal

Memory Layout

Flash Memory (64KB):
├── 0x08000000 - 0x08003FFF: Bootloader (16KB)
└── 0x08004000 - 0x0800FFFF: Application (48KB)

RAM (20KB):
├── 0x20000000: Magic number location
└── 0x20000010 - 0x20004FFF: Available for bootloader/app

Building

Prerequisites

• ARM GCC toolchain (arm-none-eabi-gcc)
• Make utility
• ST-Link tools (for flashing)

Clone and Build

# Clone the repository
git clone <repository-url>
cd simpleboot

# Build the bootloader
make all

# Flash to device
make flash

# Clean build files
make clean

Build Output

After successful build, you'll find:

• build/bootloader.elf - ELF file for debugging
• build/bootloader.hex - Intel HEX file
• build/bootloader.bin - Binary file for flashing

Usage

Entering Bootloader Mode

The bootloader will enter update mode if any of these conditions are met:

1. Button Press: Hold the button (PC13) during reset
2. Magic Number: Set magic number 0xDEADBEEF at RAM address 0x20000000 and reset
3. No Valid Application: When no valid application is found in flash

Firmware Update Process

1. Connect UART: Connect your serial terminal to USART1 (115200 baud, 8N1)
2. Enter Bootloader: Use one of the entry methods above
3. Start Transfer: Use a Y-modem capable terminal (like Tera Term, PuTTY, or minicom)
4. Send Firmware: Select your application binary file for Y-modem transfer
5. Wait for Completion: Bootloader will program flash and verify
6. Automatic Boot: After successful update, bootloader jumps to application

Terminal Commands

The bootloader sends status messages via UART:

Entering bootloader mode
Waiting for firmware... Send file using Y-modem
Starting Y-modem reception...
Firmware received, programming flash...
Flash programming completed!
Verifying firmware...
Firmware verification successful!
Starting application...

Update Application

NOTE: BOOTLOADER LOG use same usart with ymodem, so need skip some chars

• sz/rz

sz --delay-startup=2 -v --ymodem example_app/build/app.bin < /dev/ttyUSB0 >/dev/ttyUSB0

• Xshell/PuTTY/minicom/moserial

just use ui, send file with ymodem protocol

Application Development

Linker Script Configuration

Your application must be configured to start at 0x08004000:

MEMORY
{
  FLASH (rx) : ORIGIN = 0x08004000, LENGTH = 48K
  RAM (xrw)  : ORIGIN = 0x20000010, LENGTH = 20K - 0x10
}

Vector Table Relocation

In your application's main() function:

int main(void) {
  // Relocate vector table to application area
  SCB->VTOR = 0x08004000;

  // Your application code here...
}

Triggering Bootloader from Application

To enter bootloader from your application:

// Set magic number and reset
*((uint32_t *)0x20000000) = 0xDEADBEEF;
HAL_NVIC_SystemReset();

File Structure

simpleboot/
├── example_app/            # example application support OTA
├── Src/
│   ├── main.c              # Main program and system init
│   ├── bootloader.c        # Bootloader core functionality
│   └── ymodem.c           # Y-modem protocol implementation
├── Inc/
│   ├── bootloader.h        # Bootloader definitions
│   ├── ymodem.h           # Y-modem protocol definitions
│   └── stm32f1xx_hal_conf.h # HAL configuration
├── startup/
│   └── startup_stm32f103c8tx.s # Startup assembly file
├── linker/
│   └── STM32F103C8TX_BOOTLOADER.ld # Linker script
├── lib/                    # STM32 HAL library files
├── build/                  # Build output directory
├── Makefile               # Build configuration
└── README.md              # This file

Configuration

Key configuration parameters in inc/bootloader.h:

#define APPLICATION_START_ADDR 0x08004000  // App start address
#define BOOTLOADER_UART_BAUDRATE 115200   // UART baud rate
#define BOOTLOADER_TIMEOUT_MS 5000        // Timeout for user input

Y-Modem Protocol Details

The implementation supports:

• 128-byte and 1024-byte packets
• CRC16 error detection
• Automatic retry on errors
• File size information

Troubleshooting

Common Issues

1. Bootloader won't enter:

   • Check button wiring and pull-up resistor
   • Verify UART connections
   • Ensure proper reset sequence

2. Y-modem transfer fails:

   • Check UART settings (115200, 8N1)
   • Verify terminal software Y-modem support
   • Try different terminal software

3. Application won't start:

   • Verify application starts at 0x08004000
   • Check vector table relocation
   • Ensure application size doesn't exceed 48KB

4. Flash programming errors:

   • Check if flash is write-protected
   • Verify application binary format
   • Ensure sufficient flash space

Debug Options

Enable debug output by defining DEBUG=1 in Makefile:

make DEBUG=1 all

License

This project is provided as-is for educational and development purposes.

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Test thoroughly
5. Submit a pull request

Support

For issues and questions:

• Check the troubleshooting section
• Review STM32F103 reference manual
• Consult STM32 HAL documentation

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Note: Always test the bootloader thoroughly before deploying to production devices. Keep a backup method to recover the device if bootloader becomes corrupted.