STM32 Bootloader: Upgrade Firmware from Web Browser via USB

Name: STM32 Bootloader: Upgrade Firmware from Web Browser via USB
Rating: 4.9 (12 reviews)

Build a secure STM32 bootloader with AES encryption, CRC-32 checksums & web-based flasher using Web Serial API

Created byGeorgy Moshkin

Last updated 11/2025

English

English [Auto],

What you'll learn

Develop an HTML-based firmware updater
Protect firmware update files from hacking
Build a custom communication protocol
Add CRC-32 checksums for data integrity
Perform erase, read and write operations
Configure and use USB CDC on STM32F103

Course content

7 sections • 29 lectures • 2h 17m total length

Firmware Upgrade Process Demonstration1:26
Understanding the Firmware Upgrade Process3:16
Software Used to Build Examples1:19
Use STM32 cube IDE to write code and perform read, write, flash, and reboot operations, with notepad plus plus for firmware editing and web browser testing via Web Serial API.
STM32F103C8T6 Flash Memory Organization

Configuring the STM32 for USB Connectivity5:26
Receiving Data from the Microcontroller Using JavaScript7:45
Learn to receive data from a microcontroller using JavaScript and the Web Serial API by building a simple html interface that displays received bytes in hexadecimal and decimal.
Sending Data to the Microcontroller Using JavaScript5:06
Seamless USB Re-enumeration Without Unplugging1:57
Trigger usb re-enumeration without unplugging by pulsing the stm32 f103 usb d+ pin low for 100 ms using hal gpio initialization, configuring a12 as gpio output to reset the pin.
USB Serial Connection

Command 0x01: Device Identification and Firmware Version8:24
Command 0x02: Read 32-bit Data Word from Flash Memory4:42
Command 0x03: Erase the Main Application Flash Memory Region2:06
Command 0x04: Write 32-bit Data Word to Flash Memory5:00
Command 0x05: Switch Between Bootloader and Main Application1:33
Command 0x05 switches to the main application by resetting the microcontroller; the bootloader checks the backup register and returns a one-byte hex response, similar to 0x03 erase flash.
Custom Communication Protocol

Reading from the Flash Memory8:38
Erasing the Flash Memory4:09
Erase 64kB of undocumented flash on stm32 f103; bootloader memory remains. Verify the erase with stm32 cube programmer and implement a web interface erase flash button using zero three command.
Writing to the Flash Memory7:51
Write to STM32 flash memory using a web-based bootloader. Send erase and write commands, format data into four-byte blocks, and verify with STM32 cube programmer.
Storing Main Application at a Different Flash Address2:25
Using Backup Registers to Implement Boot Logic12:20
STM32F103 Flash & Backup Register: Tricky Operations Quiz

CRC-32 Calculation9:57
Add a CRC-32 checksum feature to the bootloader by implementing a Crc32 function and a lookup table, with per-byte updates and an initial CRC value, and validate using command 0x06.
Modifying Protocol to Read Larger Data Chunks3:48
Enhance the stm32 bootloader protocol to read larger data chunks over usb by adding a read n parameter to command zero two, enabling 1–255 byte reads and faster flash access.
Modifying Protocol to Write Larger Data Chunks4:30
Adding a Checksum Field to Read Command4:24
Add a crc32 checksum field to read commands and extend responses; calculate and verify data checksums in C and JavaScript, and validate flash data with cube programmer.
Adding a Checksum Field to Write Command3:26
Adding CRC-32 checksum

Write-Protecting the Bootloader4:07
Validating Main Application Integrity at Boot Time8:22
Alternative Bootloader Activation Methods1:55
Activate the bootloader via power-on and reset checks with gpio inputs or a serial command within a short window, then jump to the main application only if the checksum passes.
Unbrickable bootloader
Thank You And Next Steps0:33
Thank you for taking the STM32 Bootloader course! I hope you enjoyed the Web Serial API approach—flashing via a browser makes things so much easier. If you have questions, just drop them in the Q&A or message me directly. Happy coding!

Requirements

You need to have significant STM32 development experience using HAL with STM32CubeIDE on Windows
You need basic HTML/JavaScript experience or willingness to learn independently
Required Hardware: STM32 Blue Pill board with authentic STM32F103C8T6 microcontroller (no clones)
STLink v2 or other debugger
System Requirements: Windows 10/11 with Microsoft Edge browser

Description

Note: This course currently only supports the STM32F1 series (Blue Pill boards with STM32F103C8T6).

This course focuses on USB-based firmware upgrades (wired connection) using Web Serial API – not internet/Wi-Fi updates.

This course is for developers who want to watch code being written line-by-line. I explain concepts slowly and clearly, but the screen recordings are intentionally sped up 2x to save time. If you want to code along with every example (great for learning!), you'll need to pause and rewind frequently.

That's it – no diagrams or deep dives into flash memory theory. We'll modify STM32 and HTML code bit by bit and immediately test how it works. The screen is always split:

• Left side: Web browser + IDE (live coding)

• Right side: Slides (key concepts)

Take this course if you're into STM32 HAL and want to build a reliable, production-ready bootloader. While we focus on USB CDC and Web Serial API, the core concepts can easily adapt to UART-based bootloaders or EXE flasher utilities.

To simplify things, I've prepared helper functions for Web Serial API and STM32 USB-CDC (see myserial.js and usb_serial.c).

The course won’t explain the internals – experienced developers will quickly grasp how they work (the code is minimal)
Beginners: Try using them as-is first, but ask me if you get stuck adapting them to your projects

Who this course is for:

STM32 developers who need to implement a production-ready custom bootloader
Engineers upgrading their skills with custom protocol design

STM32 Bootloader: Upgrade Firmware from Web Browser via USB

What you'll learn

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Course content

Quick Introduction3 lectures • 6min

Setting Up USB Communication Between STM32 and Web Browser4 lectures • 20min

Design of Basic Communication Protocol for Firmware Upgrades5 lectures • 22min

Reading, Writing, and Executing Code from Different Flash Memory Addresses5 lectures • 35min

Advanced Feature #1: CRC-32 Checksum5 lectures • 26min

Advanced Feature #2: Protecting Firmware Files from Reverse Engineering3 lectures • 13min

Advanced Feature #3: Unbrickable Bootloader4 lectures • 15min

Requirements

Description

Who this course is for: