Reverse Engineering Apple’s Mikey Chip

On the previous iPods, typically referred to right here sooner or later as iPod Classic, there lives a tiny, undocumented chip known as Mikey. It sits on the headphone output and performs solely two capabilities: powering the Apple wired headset microphone and dealing with button presses from the three buttons. Despite these headphones and iPods having existed for practically 20 years, no one in the open source community has figured out the protocol Apple used for these buttons until now.

As [Hemant] found after discovering a single archived weblog publish from 16 years in the past about it, the chip is comparatively easy by trendy requirements. Besides dealing with microphone bias, it sits on an I2C bus and displays presses from the three buttons on the headset. Each button has its personal resistive load, so a press from any of them drops the voltage on the road to a specific amount which the chip can learn. The extra concerned half is a “chirp” that’s a form of handshake between headset and iPod, which took a bit of labor with a debugger that [Hemant] constructed right into a customized Rockbox firmware.

With the chirp sorted out, [Hemant] constructed the function into an present model of Rockbox, and submitted the replace to the Rockbox staff for integration in future official builds. It’s a protracted overdue function for these nonetheless utilizing wired headphones and iPods from the flip of the century, however welcome. Some of these iPods are nonetheless working to today, but only conditionally if they’re very cold.