Storing 2 bytes of data in your Logitech mouse

4 hours ago

The author had a 'dumb idea' to use a Logitech MX Vertical mouse as a tiny USB drive for data storage.
Logitech mice use the HID++ protocol, partially documented and partially reverse-engineered, with 33 features exposed.
HID++ 2.0 involves a feature table where each feature ID maps to a device-specific index, used for subsequent calls.
Attempts to use undocumented features like 'TemplateBytesNVS' for non-volatile storage were made, but some were blocked by macOS's IOHIDManager.
The device name register accepted writes but ignored them, while the DPI register successfully stored and retained a 2-byte value across devices.
The project, though yielding only 2 bytes of storage, provided deep insights into HID++, macOS HID management, and device behavior.
The investigation emphasized learning through experimentation rather than documentation, uncovering unexpected behaviors and system limitations.
The author concludes that the value was in the exploration and understanding gained, not the practical outcome.
A Rust tool was developed for this purpose and is available on GitHub for others to experiment with their Logitech mice.

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