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Atari coding BBS
| Screen addr update on Falcon |
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Posted by: Orion
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May,19.2021-23:37
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Hi guys,
I have a question for the Falcon experts!
On ST, the video base address is reloaded at HBL 310 (3 HBL before the next VBL, at 50 Hz).
Therefore, if the video base address ($ff820[1,3,d]) is modified just after VSYNC (after the VBL has started), the change will not be effective until the next VBL.
How does this work on Falcon? When is the video base address reloaded?
I have an intro that uses double-buffering and flips the screen right after VSYNC.
It works as expected on ST, but on Falcon (with the VIDEL configured in ST backwards compatible mode), it seems that the update of the screen pointer which is done after VSYNC is taken into account immediately (thus for the current VBL) and flickering occurs.
Any idea when the video base address is reloaded by the HW on this machine?
Is this in the top "border" (between the VBLANK and the start of the displayed area)?
Does it depend on the refresh rate (50Hz/60Hz)?
When should the screen flip be performed so that it works on both ST and Falcon machines?
I cannot test it myself since I don't have a Falcon machine at home.
So any help is welcome :-)
-- Orion / Reps
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