This is where things got difficult. It turned out the chip had Code Defense made it possible for, so when it was wired up to a programmer and put into DFU mode, the firmware got cleaned.
That left [Tysonpower] with no choice but to write a new firmware from scratch, which naturally needed reverse engineering the device’s hardware. Step one read up on STM32 development and getting the toolchain working, which paved the way to getting the knob’s LED to blink. A couple more hours worth of work and some multimeter poking later on, and he was able to read the knob’s movement. He explains getting USB HID working as a nightmare due to absence of documents, but eventually he got that arranged out.
The end result is a firmware enables the volume knob to imitate a mouse scroll wheel, which can be used for tuning in many SDR plans. We believe the real success story is the experience [Tysonpower] got with reverse engineering and working with the STM32 platform.