– "Computation Structures", an old MIT course book, which uses a pedagogical processor similar to a microcoded PDP-11 or a 68k, to illustrate microcoding as the highest level of digital design – the processor they implement used a two-level microcoded processor to implement two types of processor on the same microcode interpreter engine, complete with built-in monitor/debugger.

– "The Art of Digital Design", an older course text, which culminates in the implementation of a PDP-8 clone;

Finally, if it helps look up more literature, another name for microprogramming in the literature is "interpretive microcoding" – one that makes the distinction between ye olde microprogramming and modern "microoperations" pretty clear.

It also clarifies why two-level micro-coding might exist, especially in the microarchitecture of the original 68k: you write in high-level microcode an engine interpreting a target ISA; this high-level microcode interpreter is then interpreted by low-level microcode that directly activates control lines. Two levels of interpretation seems baroque, but somehow it was fast enough for 68k workstations.

A brief history of microprogramming (2005) - https://news.ycombinator.com/item?id=32149149 - July 2022 (1 comment)

A Brief History of Microprogramming - https://news.ycombinator.com/item?id=11412846 - April 2016 (8 comments)

In fact, in evaluating the new microprocessors that were becoming available in the late 70's, "difficulty of implementing the Mesa virtual machine" was a big consideration. "Just reimplement the code generation part of the compiler" wasn't considered attractive.

Another supposed advantage of the Mesa virtual machine was: we can look at the code people are actually writing, and then reimplement the op codes to make the most common ones shorter and more efficient.

Or is there any more example?

If not can those emulation (6502…) or hardware emulation (eZ80…)

Just wonder is this still new…