Software from the dark past - Sony Network Walkman NW-E507 drivers for Linux

Remember how I used to hack Sony Network Walkman NW-E507? Well, back then, I succeeded and it did work, but soon after that the device got stolen so I never polished it up to release quality. But even though it isn't release quality and I'm not even sure the code I got is the working one (although commit history does suggest so), I decided to publish it anyway. Perhaps it will be useful to someone.