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Old 23 October 2019, 09:58   #1
sandruzzo
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Join Date: Feb 2011
Location: Italy/Rome
Posts: 1,827
Extended Vertical Blank

According to HW Manual, VB can be extended by copper, and have it enabled at the end of viewport. By extending it, is it possible to have more dma slots avilable?

"The minimum time of vertical blanking is 20 horizontal scan lines for an
NTSC system and 25 horizontal scan lines for a PAL system. The range
starts at line 0 and ends at line 20 for NTSC or line 25 for PAL. After
the minimum vertical blanking range, you can control where the display
actually starts by using the DIWSTRT (display window start) register
to extend the effective vertical blanking time. See Chapter 3, "Playfield
Hardware," for more information on DIWSTRT .

If you find that you still require additional time during vertical
blanking, you can use the Copper to create a level 3 interrupt . This
Copper interrupt would be timed to occur just after the last line of
display on the screen
(after the display window stop which you have
defined by using the DIWSTOP register)."

Alessandro
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