First piece for testing...
Test with DIVMMC, all work correct.
And now test with DIVMMC + next K-MOUSE 2016 as slave. All work stable.
CPU speed regulator slowdown only program running in zx ram. All programs/code in low 16kB (zx rom area, divmmc system, system in other external devices,...) of memory run always at full speed without slowdown effect. This cause stability of all zx rom routines as LOAD,SAVE,keyboard test stability,BASIC is always full usable.