undy wrote: ↑
Thu May 17, 2018 8:13 am
I was under the impression that wiring rpi tx -> arduino rx directly would not cause any damage to either of them (at least in the short-term), am I wrong about that?
No; you are right. It is what would be expected, what many people have done and are doing, with Arduino and other micros, without any problem.
There may be some potential issues if your Arduino is powered from 5V, more so if it has is a pull-up to 5V on its RX input, but, as Dougie notes, the Pi will be damaged in a nanosecond if there is an adverse situation, and it seemed to be working perfectly well for at least some time.
I do not think we will ever discover what has caused the problem. We can all take guesses but we'll never know for sure.
I am not however convinced that the IGPIO are all fried. Maybe they are, but perhaps not. I think you should undertake further tests to determine or confirm what the situation is.
Find a new or spare SD Card and start with a fresh install of Raspbian and don't add or install anything so you can be sure nothing else is messing with GPIO. Write two simple Python programs; one to toggle an output pin and check if that works, a second with an internal pulled-up input to see if that can read a short-to-0V on a pin.
That should give you a better idea whether GPIO are fried or not.