R800‑compatible version of MCLZ8 (kind-of 16bit CMOS Z80 found in last MSX machines) ?

[Sch-LikA]

Hi, and thanks for MCLZ8 — great project of a great family !

A little context : In the MSX community, the latest "Turbo‑R" machines have become extremely rare and expensive. Recently, a closed-source fpga based board was sold to upgrade more common late Sony MSX machines to "Turbo-R" specs, but these boards are now unobtainable (https://channel.beep-shop.com/products/detail/49363).

I think an open, reproducible alternative would be really welcomed.

Basically, the only difference between the Sony MSX2+ and the later "Turbo-R" machines is its cpu, the R800, basically a faster CMOS Z80 with only a few differences:

Same instruction set + a few extras:

• MULU / MULUW (16×16 unsigned multiply, rarely used)
• DIVU / DIVUW (unsigned 32÷16, rarely used)
• Simple pipeline → much faster instruction timings
• Reduced memory cycles
• Slightly different burst‑style bus timing

It is still fully binary‑compatible with Z80 code

I am not too sure what juice remains in the Teensy 4.1, would an R800‑style extension feels at least hypothetically possible?

Ideally, the "MCLR8" should also host a few selectable roms and some ram, but I guess that would be the most trivial part?

I would love trying to tackle that myself, but I feel I am quite a bit out of my comfort zone. This issue is also a way to see if there is some interest from other people, we may somehow collaborate on this.

Thanks again for sharing your work!

[MicroCoreLabs]

Hi! There should be plenty of power for the Teensy 4.1 to implement these new opcodes. You can also reduce or eliminate the MCLZ8 timing accuracy to allow it to run as fast or faster than the original R800. And adding ROMs and RAMs are very easy to do.

Sounds like a fun project. Please keep me up to date on the progress!