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Old 17 January 2016, 12:39   #1
Posts: n/a
Post Possible bug in Copper timing / emulation

While playing with Copper loops and jumps, i think i discovered a bug in the Copper emulation.

If you setup a Copper loop to keep spamming the Color 00 register 55 times every scanline. it gives a somewhat funny result (see attached screenshot)

there is 2 things i notice.
1. The pattern is not the same all the way down
2. On the right side of the screen, there is a "step" where the colorshift takes up more than 8 pixels. (i think about 10 pixels)

i would expect this code to repeat the same pattern all the way down the screen, but instead it changes about half way down the screen to another pattern. If i add more color shifts to the copperlist, it will also change to a straight pattern about half the way down the screen.

i have testet with different WinUAE versions, and the result is the same.
I have not testet this on real hardware, as i don't have it setup right now.

attached is:
WinUAE Copper bug.png : Picture of the screen i see
WinUAE CopperBug-Small.s: Sourcecode to reproduce the issue
WinUAE-CopperBug.lha: Exe file to show the issue
Amiga 1200.uae: The UAE configuration used.

I dont know if this is a bug, or expected behavior, but it makes very little sence to me.

Attached Thumbnails
Click image for larger version

Name:	WinUAE Copper bug.png
Views:	198
Size:	50.6 KB
ID:	46997  
Attached Files
File Type: s WinUAE CopperBug-Small.s (1.9 KB, 31 views)
File Type: lha WinUAE-CopperBug.lha (347 Bytes, 26 views)
File Type: uae Amiga 1200.uae (18.5 KB, 18 views)
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