Max, I enjoyed reading your article. Interestingly, no one commented on microcode, which is “bare metal” programming. I learned about this in the mid-80's while microcode programming an Adage graphics ...

COMP.2030 — Undergraduate Id: 008066 Offering: 1 Credits: 3-3 Description Presents the organization and operation of a conventional computer, including principal instruction types, data representation ...

But you can get a great starting tutorial with the 21 programs on the ARM Assembly by Example website. You need a 32-bit ARMv6 or better — so Raspberry Pi will work here.