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WebTool: A Secure Loader

The WebTool (the browser-based flasher) no longer calculates security features; it only acts as a transfer interface.

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📥 Input Files

The WebTool should only receive binary files (*.bin) that have already been pre-signed by the Offline Signer Tool.
  • The file contains the application code PLUS the 28-byte Security Footer.

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🔄 Transfer Protocol

The flashing process follows the traditional USB CDC protocol, treating the signed file as a single complete payload:
  1. Start: The WebTool sends HELLO and then ERASE APP to clear the application space.
  2. Writing: The WebTool sends the entire signed file in chunks using the command WRITE addr len crc32 and the binary payload.
  3. Finalization: The DONE command is sent.
  4. Activation: The Bootloader receives the data, writes it to Flash (including the footer in its final location), and reboots.

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⏱️ Timeout Management

To ensure the flashing process does not fail prematurely if unauthorized firmware is loaded, the WebTool waits for an extended period:
  • Increased Delay: The final waiting time after sending DONE has been extended to 20 seconds.
  • Purpose: This time covers the 15-second delay imposed by the Bootloader if the authenticity check fails, ensuring the USB connection is not cut before the device can reboot or enter waiting mode.