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Old 24 April 2003, 15:29   #18
Toni Wilen
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 42
Posts: 19,668
Disassembly from CD-demo:

1005137c 2039 00df f104           MOVE.L $00dff104,D0
10051382 0280 0001 ff00           AND.L #$0001ff00,D0
10051388 0c80 0001 1800           CMP.L #$00011800,D0
1005138e 66ec                     BNE.B #$ffffffec == 1005137c
10051390 41f9 1028 48bc           LEA.L $102848bc,A0
Uh, oh. first line should be most likely MOVE.L $dff004,d0 (read hpos and vpos, not read from write-only BPLCON2 and BPLCON3..) This probably works on real Amigas by accident.

Reading from write-only/non-existing registers return something interesting depending on many things like chipset type, state of other dma channels etc... WinUAE emulates this about 90% correctly only in 68000/ECS Agnus-mode..

Easy workaround: wait until demo freezes, press SHIFT+F12 (in windowed mode), type d<return>, check address after BNE.B-line. type g <address><return> (10051390 in this example) and demo continues.
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