Ed SCan I recommend RISC OS Pico? It's a tiny RISC OS for your Raspberry Pi, boots instantly to BBC Basic (black screen, white text) but there are plenty of commands to do old-school graphics in a number of old, and new, screen resolutions. And of course the Basic has an ARM assembler built in!
(This is a single-tasking and GUI-free version of RISC OS. Surely a good one for #retronauts)
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