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STM32F723 Flash Programmer

Browser-based USB DFU flash programmer for the STM32F723, using the factory ROM bootloader over USB Full-Speed. No drivers, no desktop software — runs entirely in Chrome via the WebUSB API.

Project Plan

Goal

Program the STM32F723 flash from a .hex or .bin file through the device's built-in ROM bootloader (USB DFU / DfuSe mode), erasing and writing only the flash sectors touched by the file. All other flash is left intact.

Architecture

Pure HTML/JS/CSS — no build step, no npm, no server-side component.

stm32programmer/
├── index.html          UI shell
├── style.css           Dark theme
└── src/
    ├── hex-parser.js   Intel HEX + BIN parser  →  [{address, data}]
    ├── dfu.js          DfuSe protocol over WebUSB
    └── app.js          Event wiring, USB lifecycle, progress

Protocol

The STM32 ROM bootloader exposes a USB DFU class device (DfuSe variant):

Field Value
USB VID 0x0483 (STMicroelectronics)
USB PID 0xDF11 (DFU mode)
Transfer size 2048 bytes
Protocol DFU 1.1 + ST DfuSe extensions

DFU operations used:

Request Code Purpose
DNLOAD 0x01 Write block / special command
UPLOAD 0x02 Read block (verify)
GETSTATUS 0x03 Poll state machine
CLRSTATUS 0x04 Clear error
ABORT 0x06 Return to dfuIDLE

DfuSe special commands (sent as DNLOAD wBlockNum=0):

Byte 0 Command Effect
0x21 SET_ADDRESS Set base address for subsequent data blocks
0x41 ERASE Erase the sector containing the given address

Write sequence per segment:

  1. Erase each overlapping sector via ERASE command
  2. SET_ADDRESS to segment start
  3. DNLOAD wBlockNum=2,3,4… for each 2 KB chunk
  4. (Optional) UPLOAD to read back and verify byte-by-byte
  5. (Optional) SET_ADDRESS(0x08000000) + zero-length DNLOAD wBlockNum=2 to trigger jump to app

STM32F72x/73x Flash Sector Map

Sector Start Size
0 0x08000000 16 KB
1 0x08004000 16 KB
2 0x08008000 16 KB
3 0x0800C000 16 KB
4 0x08010000 64 KB
5 0x08020000 128 KB
6 0x08040000 128 KB
7 0x08060000 128 KB (xE 512 KB variant only)

The app auto-detects the map from the DfuSe interface string descriptor. The hardcoded table above is the fallback.

Instructions for Use

1. Enter DFU Mode on the STM32F723

  1. Pull BOOT0 pin high (connect to VCC or assert via solder bridge/switch).
  2. Reset the device (press reset button or cycle power).
  3. The STM32 will enumerate as a DFU device — no firmware runs.

Confirm the device is visible:

  • macOS/Linux: lsusb → should show STMicroelectronics STM Device in DFU Mode
  • Windows: Device Manager → Universal Serial Bus devices → STM Device in DFU Mode

2. Start the Local HTTP Server

WebUSB requires a secure context (HTTPS or localhost). Start the server from the project folder:

cd /path/to/stm32programmer
python3 -m http.server 8080

Then open Chrome (not Safari, Firefox, or Edge) and navigate to:

http://localhost:8080

3. Load a Firmware File

  • Drag and drop a .hex or .bin file onto the drop zone, or click to browse.
  • For .hex files: target addresses are read from the file automatically.
  • For .bin files: enter the Flash address where the binary should be loaded (default 0x08000000).

The status line shows the number of segments and total byte count.

4. Connect the Device

Click Connect Device. Chrome will show a USB device picker — select the STM32 DFU entry.

On success the device name and sector count appear. If the DfuSe interface string is readable, the exact sector map for your variant is used automatically.

5. Program

Click Program Flash.

Progress is shown in three phases:

Bar What it shows
Erase Sectors erased / total sectors to erase
Write KB written / total KB
Verify KB read back and confirmed (if enabled)

Verify after write (checked by default): reads every written byte back from flash and compares it to the source file. The first mismatch is reported with its address and both values.

Leave DFU & reset (checked by default): after programming (and verify), triggers the ROM bootloader to jump to 0x08000000 and run your firmware. The device will disconnect from USB.

Checkboxes at a glance

Option Default Effect
Verify after write ✓ on Read-back and byte-compare every written address
Leave DFU & reset ✓ on Jump to application after programming

Troubleshooting

Symptom Likely cause Fix
"WebUSB not available" Not Chrome, or not on localhost/HTTPS Use Chrome at http://localhost:8080
Device not listed in picker Not in DFU mode Check BOOT0 and reset
"Access denied" or "device in use" Another tool (STM32CubeProgrammer, dfu-util) has the device Close the other tool
Verify mismatch Write error or wrong address Check that the hex/bin targets the correct flash region; retry
Device disconnects mid-write USB cable issue or device reset Use a short, quality USB cable; retry
"Cannot reach idle state" Device stuck in error Disconnect, power-cycle the STM32, reconnect