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Published 20 hours ago • verified publisher icon MicroCoreLabs

MCLZ8 - Fetch_opcode() is wrongly used to retrieve immediate values, displacements or offsets in an instruction.

Open hlide opened this issue 2 years ago • 1 comments

This function is called too often wrongly to retrieve immediate values, displacements or offsets in an instruction. You should use a MEM_READ_BYTE (3 T-states) and not an OPCODE_READ_M1 (4 T-states) for them! https://github.com/MicroCoreLabs/Projects/blob/26b2c2701e403da5991a13c1879093d4e3dbf226/MCLZ8/Code/Standard_Z80/MCLZ8.ino#L629

There is no M1 = 0 and no refresh when retrieving immediate values, displacements or offsets in an instruction!

See here a complex example here: https://floooh.github.io/2021/12/06/z80-instruction-timing.html#dd-and-fd-prefixes. Be aware the table are showing steps per half-cycle (half T-state) so a MEM_READ_BYTE would be 6 rows for 3 T-states.

hlide avatar Jan 24 '23 10:01 hlide

Thank you for finding this bug! Code updated.

MicroCoreLabs avatar Jan 29 '23 04:01 MicroCoreLabs