ExtFlashUploader – STM32F103 + W25Q64 External Flash Programmer

ExtFlashUploader is a bare-metal firmware running on STM32F103C8T6, designed to manipulate memory regions directly and upload application images from internal Flash to external W25Q64 SPI NOR Flash.
It also generates a metadata table (valid flag, address, size, CRC32) which is later used by the Bootloader for program validation and vector table relocation.

This project demonstrates low-level memory management, Flash programming sequence, and system integration in embedded environments — making it a showcase for both firmware engineering and bootloader design.

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🚀 Key Features

• Direct memory access: Reads application image directly from STM32 internal Flash (0x0800xxxx) via memory-mapped addresses
• External Flash programming: Erase (4KB sector) + Page Program (256 bytes) to W25Q64
• Hardware CRC32: Utilizes STM32 CRC peripheral for data integrity check
• Metadata management: Writes metadata structure into sector0 of external Flash for Bootloader reference
• Multi-repo support: Store multiple application images with independent metadata entries
• Optional OLED display: Shows status (Done) for user confirmation

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📦 Hardware Requirements

• MCU: STM32F103C8T6 (ARM Cortex-M3)
• External Flash: W25Q64 (64Mbit(8MB) SPI NOR Flash)
• OLED Display (I2C, optional for status output)
• Interfaces:
  • SPI1 for W25Q64 access
  • GPIO/I2C for OLED

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🗂 Metadata Layout

Field	Size	Description
ValidFlag	4 Bytes	Constant 0xA5A5A5A5 = valid entry
Address	4 Bytes	Start address in external Flash
Size	4 Bytes	Program size (bytes)
CRC32	4 Bytes	Integrity check (STM32 hardware CRC32 result)

Example (Hex Dump):

----------------------------------------------------------
| Repo | ValidFlag   | Address   | Size     | CRC32      |
----------------------------------------------------------
|  1   | A5A5A5A5    | 0x001000  | 0x00023C | 0x5E3B9A7C |
|  2   | A5A5A5A5    | 0x005000  | 0x0001E0 | 0x4D92ABF1 |
----------------------------------------------------------

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🔄 Workflow

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🔗 Integration with Bootloader

ExtFlashUploader prepares external Flash with:

• Application image(s) written at fixed addresses
• Metadata table at sector0 for validation

The Bootloader then:

• Reads metadata entries
• Verifies CRC32
• Relocates vector table
• Jumps to the selected application (Repo1, Repo2, etc.)

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🗺 External Flash Memory Map (W25Q64 – 8 MB)

Address Range	Size	Usage
0x000000 ~ 0x000FFF	4 KB	Sector 0 – Metadata Table
0x001000 ~ ...		Application Images (Repo1, Repo2, ...)
... ~ 0x7FFFFF	~8 MB	Remaining space for image storage

• Metadata Table (Sector 0)
  Stores multiple entries, each describing one application image:

  • ValidFlag (0xA5A5A5A5)
  • Address (image start in external Flash)
  • Size (image size in bytes)
  • CRC32 (integrity check)

• Application Images
  Each repo is placed in the Flash starting from 0x001000, aligned to sector boundaries (4 KB).
  Example:

  • Repo1 @ 0x001000
  • Repo2 @ 0x005000
  • Repo3 ... etc.

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⚡ How to Use

1. Flash ExtFlashUploader into STM32F103 using Keil or STM32CubeProgrammer.
2. On reset, the firmware automatically:
   • Reads the specified memory region in internal Flash (application image).
   • Performs sector erase on the target region of external Flash.
   • Executes page programming (256 bytes per write) into W25Q64.
   • Calculates CRC32 checksum via STM32 CRC peripheral.
   • Stores metadata structure in external Flash sector0.
3. OLED (if connected) shows Done upon success.
4. Bootloader then validates metadata, checks CRC, and jumps to the selected repo.

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🎯 Professional Highlights

This project emphasizes low-level firmware engineering skills highly relevant to embedded R&D roles:

• Direct manipulation of memory-mapped regions in internal Flash
• Implementation of Flash programming protocol (Erase / Program / CRC)
• Handling metadata structures for multi-image bootloader systems
• Integration with Bootloader for image validation and jump execution
• Demonstrates system-level thinking: from binary image handling to runtime execution flow

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