A chip called Mikey has sat undocumented inside iPod Classic headphone jacks for nearly two decades. It handles exactly two things: microphone bias power and button presses from Apple's 3-button wired headsets. No one in the open source community had cracked its protocol until Hemant did it now.
The mechanism is straightforward once exposed. Each button applies a distinct resistive load, dropping line voltage to a readable level over I2C. The hard part was a handshake signal Hemant calls a 'chirp', which required building a custom debugger directly into Rockbox firmware to capture and decode. That single engineering detail is what kept this locked for 16 years, and the original article walks through exactly how he isolated it.
Hemant has already submitted the working implementation to the Rockbox project for inclusion in future official builds. That means wired headset button support on iPod Classic hardware, running open firmware, solved cleanly and permanently. The full write-up is worth reading for the debugging methodology alone.
[READ ORIGINAL →]