[thomspoon]

Imo there’s not really a best book or resource other than buying a microcontroller and doing it yourself! Pick up a ARM Cortex-M4 development board either from TI or STM and reimplement their example code or driver code in assembly! You can look at the ISA to see what assembly instructions are supported, or the disassembly of a running program (probably with no optimizations so you can see what they are doing)

[jagger27]

There’s definitely something to be said about poking a physical pin in assembly. It makes me feel like I actually have control of the computer, and that I’m not just along for the ride.