I worked on this project a bit back in the day as a teen. Bricked my first iPod trying to get a DIY uClinux kernel to boot on it within hours of getting it for Christmas. Took bricking 8 more warranty replacements before I finally got Linux to boot.
Weeks later thanks to a lot of community help, finally found the memory address for audio out and got music playback that was not beholden to any DRM.
This work was all referenced by the RockBox team that made a tiny embedded kernel and OS far more suited to the tasks.
Now all devices that can run rockbox are EOL and other community members are working on an open hardware player to run Rockbox.
https://github.com/amachronic/echoplayer
Couple decades in, but we are finally close to having the first fully featured fully open hardware music player, which all started back with reverse engineering iPods to run Linux kernels.
As someone that does not carry a cell phone, I am absolutely excited about this as it would be a daily driver for me.
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