06 March 2016, 13:18 | #1 |
Lemon. / Core Design
Join Date: Mar 2016
Location: Tier 5
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When is the modulo added to the bitplane pointers?
Is it as soon as DDFSTOP is reached, or is it at DDFSTART position? or some unknown position between the two?
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06 March 2016, 14:05 | #2 |
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 49
Posts: 26,583
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Modulo is added when plane's last DMA fetch is done, after DDFSTOP, plane by plane.
Remember that DDFSTOP (quite unintuitively) means that following complete "bitplane block" (all planes fetched) will be the last one, DDFSTOP isn't actual stopping position. |
06 March 2016, 14:19 | #3 |
Lemon. / Core Design
Join Date: Mar 2016
Location: Tier 5
Posts: 1,213
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Thanks Toni, Good to know.. Not something I ever really thought about before..
just that I was thinking of using modulo rather than bitplane pointers on a particular scanline, to do the split, for vertical scrolling. EDIT: Seems I can't Would be a modulo of 40,000 and something... or.. negative number in word size |
07 March 2016, 18:24 | #4 |
Moderator
Join Date: Nov 2004
Location: Eksjö / Sweden
Posts: 5,738
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HPOS for modulo read can be checked quickly with a test-Copper, grr!
To bring down the modulo to +-$7ffe you can de-interleave completely or partially. Which may affect the bob routine speed, of course. |
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