How to set BUSREQ or WAIT? about z80 HOT 1 CLOSED

WAIT is not explicity set by using any function. Instead, you should directly add to Z80::cycles the desired wait T-states. Do it within the callback corresponding to the M-cycle in which the WAIT signal is generated.

As for BUSREQ, there is a limitation, although I have not yet explained it adequately in the documentation: A real Z80 CPU responds to the BUSREQ signal at the end of each M-cycle. That means that as long as the signal lasts, the M-cycle is frozen and the CPU does not go to the next one until the signal ends. If the signal is short, this can be emulated in the same way as WAIT, that is, by adding to Z80::cycles the duration of the signal. However, if the signal is very long, for example in the case of a DMA operation that moves a large amount of memory or similar, then we have the problem that, even if we add the T-states:

1. if that amount makes the global T-state counter of your machine object exceed the total T-states of 1 emulated machine frame,
2. and the signal does not occur in the last M-cycle of the instruction,
3. and there are still others in which memory will be accessed,

problems may arise (depending on what is being emulated and whether a precise control of the T-state within the frame in which a memory access is performed is required, of course).

I think the best solution is to handle BUSREQ in your side between your calls to z80_run or z80_execute, and assume that the signal always starts during the last M-cycle of an instruction.

The alternative would be to save the state of the Z80 object and use setjmp() or similar in the callback where the signal occurs to avoid finishing executing the instruction. But I don't think it would be worth it, it would be quite complex to do.

from z80.