My mom had an old Roku that she no longer wanted so I took it figuring I might be able to hack it and run a generic Linux on it. I took it apart and saw two headers that looked like they might be for debugging. I found the ground (on what I'm calling pin 2) and then probed the rest and found out they are all 3.3V (at least on P12). I hooked up my logic analyser to all the pins and rebooted, found a 115200 baud signal on what I am calling pin 6. Looking at the data it says "U-boot..." then "Linux 2.6.4-roku..." so I think I have the right pin.
My question is how could I go about finding the RX pin? I have a Raspberry PI which has a 3.3V uart and one of these https://www.sparkfun.com/products/9873. Is there a safe way to do it? Is there a standard header that has 10 pins with ground on 2 and tx on 6?
In the pictures I left the logic analyser hooked up. https://imgur.com/a/UL80fPe