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Old 08 April 2019, 04:26   #18
ReadOnlyCat
Code Kitten

 
Join Date: Aug 2015
Location: Montreal/Canadia
Age: 48
Posts: 1,143
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.
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