Have to change my approach, perhaps using invariant (table of full instruction chrono versus reality), validate instruction timing before trying validating IO_ACK interrupts. Write one table from plustest.dsk's testbench launched on WinAPE, and table from original Z80 documentation, and deduce the table of latencies. I have to trust first in my instruction timing tables (and have to write them both completely...)
Prefixed instruction has only one M1 ?
=== Test of a real Zilog 80 ===