English Amiga Board - View Single Post

ReadOnlyCat · 08 April 2019, 03:26

My previous post about color changes interleaving made me think that since nasty-mode Blitter timings are fairly computable/predictable it should be doable to organize the Copper list in a way which makes it relatively easy to handle and detect the

VBLANK

transition.

Assuming one can organize blits and/or predict their duration precisely enough, the Copper list could be constructed in a way that slightly ahead of the

VBLANK

transition it would insert a large blit that takes a known number of scanlines and is guaranteed to terminate well into the next frame. The Copper could then be instructed to simply jump into next-frame's list where it would wait for that blit to finish normally.

It seems feasible for blit-list construction routines to keep track of the current DMA budget while they queue up new blits and to insert a previously-put-aside large blit when they detect that the budget is almost exhausted.

The advantage of such a technique is that it would allow to lift the requirement to use only idempotent blits.

08 April 2019, 03:26	#18
ReadOnlyCat Code Kitten Join Date: Aug 2015 Location: Montreal/Canadia Age: 52 Posts: 1,178	My previous post about color changes interleaving made me think that since nasty-mode Blitter timings are fairly computable/predictable it should be doable to organize the Copper list in a way which makes it relatively easy to handle and detect the VBLANK transition. Assuming one can organize blits and/or predict their duration precisely enough, the Copper list could be constructed in a way that slightly ahead of the VBLANK transition it would insert a large blit that takes a known number of scanlines and is guaranteed to terminate well into the next frame. The Copper could then be instructed to simply jump into next-frame's list where it would wait for that blit to finish normally. It seems feasible for blit-list construction routines to keep track of the current DMA budget while they queue up new blits and to insert a previously-put-aside large blit when they detect that the budget is almost exhausted. The advantage of such a technique is that it would allow to lift the requirement to use only idempotent blits.