Version 4 of the PCB has arrived and been assembled. I switched around what GPIO is being used for what so that I could add an SD card to the spi interface, but now keypad scanning isn't working properly. The top two rows recognize all keys in the row as being pressed if any key in the row is pressed. Not sure yet if this is just a software thing, or if I'm using GPIO pins that have different pull-up resistor criteria, since those rows are ones that are using different pins now. I may have to do another board version with external pull-up resistors.

Since the code is misbehaving, I'm taking the opportunity to clean stuff up and add more comments. Doesn't do anything to the code, and it makes it easier for anyone else to load it up and figure out what I'm doing. I've had to reverse-engineer weird code too many times. The less of that in the world, the better so far as I'm concerned.