Some bare-metal Pi resources for retrocomputists

Here are some I know of:
PiTubeDirect (second processor for Acorn 8 bit micros, bit-bangs a read-write peripheral on the 2MHz bus)
RGBtoHDMI (samples RGB video and presents as pixel-perfect HDMI, very low latency, uses a CPLD as deserialiser and optional analogue front end board for multi-level signals such as from Amstrad)
Pi1MHz (multi-purpose peripheral for Acorn 8 bit micros, bit-bangs a read-write peripheral on the 1MHz bus)

PiTubeDirect is notable for using part of the GPU to bit-bang the peripheral response to the host bus, leaving the ARM core free to do the main mission, emulating a processor subsystem. There’s a very high performance 6502 emulation in there, written in ARM assembly, as well as C emulations of 6502, Z80, ns32k, PDP-11, 6809, x86, ARM2, as well as a second processor which is the Pi itself (1GHz ARM).

I found these projects and links:

ZXBaremulator

Some resources for baremetal programming:

Baking Pi – Operating Systems Development (University of Cambridge)

Ultibo core “is a full featured environment for embedded or bare metal (without an operating system) development on Raspberry Pi”

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