Did way more Arduino assembly hacking late this evening.

Get used to using Makefiles and a lot of avr-gcc and avrdude.

If you do it in the Arduino IDE, it will be completely different to doing it in Emacs. The Arduino IDE is only made for coding in C or C++, so you have to get used to keeping some vestigial amount of C in order to do any assembly programming.

Ports between different Arduino models change their addressing so you will end up scratching your head as to why everything was not kept the same.

Hard to explain, but Arduinos are not that great. The software stack is very crufty and quite bitrotted by now.

Code that is promised to just work if you download the file and compile it and upload it, manifestly does not--usually because many people using Arduinos are using Windows.

The Arduino Atmel AVR ISA is proprietary, so that just absolutely sucks.