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Old 10 August 2016, 14:59   #5
Toni Wilen
WinUAE developer
 
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 42
Posts: 19,561
Warning: technical stuff.

Hmm.. It uses DDFSTOP value $d8 but 64-bit AGA fetch mode. This combination would mean last "bitplane block" fetch start position of $d8 or later. In this case it would equal start position near the beginning of next scanline (Previous is at $b0, next would be $c8+$20 = $e8 which is >$e2). In other words there can be some undocumented side-effect happening. (Usually bitplane DMA overrun causes visible glitches but not always). This oddity causes emulation to skip modulo addition (gets too confused with fetch block that does not start until next scanline) which also can't be right

Testing needed...

It looks like game uses normal OCS/ECS DDFSTRT/STOP pair and modulo was adjusted until display become "AGA compatible". (and possibly also wasted 8 dma slots for invisible bitplane data)
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