jaleco/megasys1.cpp - use dumped MCU for bigstrik [Sergio Galiano, Recreativos Piscis, David Haywood]

[mamehaze]

• updated tlcs90 port / irq handling to match hardware, implemented halt support [Sergio Galiano, Recreativos Piscis]
• hooked up MCU support in megasys1 driver [Sergio Galiano, Recreativos Piscis, David Haywood]
• started splitting megasys1 driver into subclasses [David Haywood]
• added 2 clones [unknown]

the clone sets have been kicking around in unemulated sets since the late 90s, probably Arcade ROMs from Japan or Romlist dumps / stuff that was sent to RAINEdev or similar.

[mamehaze]

FWIW I'm done with this PR for now and feel overall it's an improvement on the existing code / driver.

Further work may be needed on cleaning up the existing driver though (but that will come later, in a separate PR once more research has been performed)

The 'Type A' "MCU" appears to not be an MCU at all for example, but an NEC Gate Array. This actually makes sense, because a gate array is much faster at the specific tasks it's programmed to perform, and anything providing a ROM overlay would need to be able to do so as fast as the 68k demanded it.

This also means the OKI status register thing is unlikely protection related (maybe a design fault on some motherboard revisions?)

Furthermore it means it's unlikely to be involved in interrupt handling (so the old Ninja Kazan solution will need revisiting)

Also at some point the sprite code needs rewriting to use the real priority PROM, not an approximation of it calculated in code.

[cuavas]

It looks like this hacks the TLCS90 core to disable edge detection on input lines to avoid needing to deassert interrupt inputs. That’s going to break other things. It would be less evil to use pulse_input_line or HOLD_LINE in the driver.

[mamehaze]

all feedback should be addressed

[cuavas]

all feedback should be addressed

Indeed, it appears so.