View Single Post
Old 23 October 2019, 10:59   #3
roondar
Registered User

 
Join Date: Jul 2015
Location: The Netherlands
Posts: 1,719
I'd say the only way to really get more DMA slots for the Blitter or CPU is to limit DMA usage for the other DMA sources. Reducing screen depth is an obvious choice, as it limiting screen width or height. Some gains are also possible by intelligently choosing how to interleave the CPU with other DMA: do as much of the CPU only work (such as game/demo logic) as possibly during bitplane fetches and only activate 'Blitter Nasty' when you have nothing left to do but wait. This optimises bus usage and allows the Blitter to use more of the non-bitplane DMA time.

In other words, don't use VBLANK for timing but rather Copper interrupts at the beginning of actual bitplane fetches. I've tested this repeatedly and found it ends up giving a small percentage of extra 'free' slots to the Blitter. Similarly, by switching Blitter Nasty on during the Blitter Wait and off afterwards, you also gain a small amount of apparent extra cycles (depending on how big the blit is and how much you can do while it runs)

Nothing amazing and usually ends up being less than 5%, but it's essentially free, so why not do it?
roondar is offline  
 
Page generated in 0.04397 seconds with 11 queries