storm_maker wrote:Bearing in mind that I'm not really much of a tech guy, how efficient actually is the Asic? would it run without much help from the CPU, or would the CPU be bottlenecking the whole capabilities?
The ASIC is just a bunch of custom logic that replaces the chips usually found in the system to do things like generate the video signal or make sounds. It doesn't really "do" anything by itself, so to speak.
Would a screen full of multiplexed sprites have been easy? with enough to use half of them to add high resolution detail and/or simple parallax to the low resolution background while still having enough left over for a game?
How about its programmable interupts? good enough for line scrolling parallax? or Mode 1 with 8 colours using a screen split?
Can the DMA stuff be used for in-game music? SFX?
Multiplexing sprites is tricky, because while they can be repositioned on-screen quickly enough, reloading a sprite image requires a lot of CPU time (unlike say the C64 where it is just a pointer into RAM, the CPC+ stores sprite images in special hardware registers). It can definitely be used within those limitation to apply a degree of parallax though, as can be seen in Prehistorik II.
Raster interrupts can be programmed to go off on any line and that lets you do some very nice colour effects (again see the backdrops in Prehistorik II), though you're still subject to how fast the CPU can update the colour palette entries. Theoretically you could fiddle with the scrolling registers too, though I've not yet figured a way of effectively using that to produce a really fluid parallax effect (though I have some cart-only ideas).
The "DMA" sound is actually one of the more interesting features. It's not really "DMA" exactly, at least in the traditional sense, rather it is a sort of simplistic co-processor which can perform simple operations free of CPU intervention. It's pretty much limited to either writing a value to a sound chip register or causing an interrupt, but it can be used to feed sound data far faster than the CPU on it's own can do. You can certainly use it for music or sound effects though which gives more time for the CPU to do other stuff.