MXE11: run UNIX on a microcontroller

Looking for an architecture that can be well-emulated with modern microcontrollers and for which there is enough tools and software there, I came across the PDP11.
The first approaches have already been made: https://dave.cheney.net/tag/pdp11 but in the end that was not optimal from my point of view. The core problem and bottleneck I see there is the external SPI RAM, but without that you will probably not get out. Or is it?
Mini Unix was developed in the 70s by Heinz Lycklama at Bell Laboratories. It’s a complete Unix V6 system, which was modified to run on only 56KBytes of RAM. And above all, no MMU is needed. Roughly enough, 64K of RAM in the controller should suffice, and there are some devices in this size class. The original project was developed on a SPC56EL60 (ST, PowerPC architecture), in addition there is an SDL port for the PC (actually two) and now some STM32 variants. Since I wanted to be more specific about the matter, I did not use an existing code (like SIMH) for the emulator, but I wrote it from scratch. Also with a view to porting parts to ASM. I have already done this on the SPC56EL60, at the moment I do not have the time to do this for the ARM variants. “

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