I got a Pinephone and decided to write a hobby mobile OS for fun. The first step is to see if I can write a bare-metal program for it. It turned out to be not very difficult, and I will show you the steps here. Preparation We need a couple of things: A Pinephone, of course. A USB to serial audio jack connector. You can buy one from Pine64 store or get a similar cable (I was able to succeed using a TTL-232R-3V3-AJ cable)....