cop2lc modified by the system

remz · 04 July 2023, 01:08

Hi Amiga coders,

Today I noticed that if I enable System to perform some file I/O, and then disable System, the value I had in COP2LC is stomped.

This is causing a visual glitch in my game since I need a CopJump to copper list 2 at a specific scanline.

While I can restore cop2lc after disabling back the system, the visual glitch will still be visible during the I/O part. I tested both KS 1.3 and KS 2.0, and in both cases the same thing happen.

Could I perhaps "counter" this by setting cop2lc at the start of my copperlist (instead of being set by cpu)?

koobo · 04 July 2023, 07:59

This is done in the system VERTB interrupt. One way to prevent this is to set up a high priority VERTB interrupt that prevents running the lower priority interrupt servers in the chain by clearing the Z flag at the end.

ross · 04 July 2023, 13:11

Or the opposite, ie a very low priority VERTB, last in the chain, where you rewrite your COP2LC.
This way you are transparent to the existing chain and don't affect it.

Or set it to your copper list slightly before the COP2JMP call.

Toni Wilen · 04 July 2023, 13:32

Doing file io without vblank can cause problems for example if some 3rd party HD driver uses vblank mode CIA timers. Don't do that, please.

KONEY · 15 February 2024, 23:35

Sorry guys if I resume this but it looks like my problem...

MainCopper won't jump to Copper2 because COP2LC value written by the CPU changes!

Setting it from MainCopper would work but I can't do it because I'm building a series of frames and each Copper2 would update COP2LC with next Copper2 so that MainCopper would always jumps to the following Copper2.

So how to fix it? Obviously I have no idea what "setting up a VERTB interrupt" means

Thanks

Wepl · 16 February 2024, 08:58

Either use the OS or switch it off. Don't mix.

KONEY · 16 February 2024, 10:13

Well it turned out a VERTB interrupt was already in place since I'm using Photon's MiniWrapper. But I disabled it long ago because it would crash with some combinations of CPU/KS.

04 July 2023, 01:08	#1
remz Registered User Join Date: May 2022 Location: Canada Posts: 139	cop2lc modified by the system Hi Amiga coders, Today I noticed that if I enable System to perform some file I/O, and then disable System, the value I had in COP2LC is stomped. This is causing a visual glitch in my game since I need a CopJump to copper list 2 at a specific scanline. While I can restore cop2lc after disabling back the system, the visual glitch will still be visible during the I/O part. I tested both KS 1.3 and KS 2.0, and in both cases the same thing happen. Could I perhaps "counter" this by setting cop2lc at the start of my copperlist (instead of being set by cpu)?

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04 July 2023, 07:59	#2
koobo Registered User Join Date: Sep 2019 Location: Finland Posts: 363	This is done in the system VERTB interrupt. One way to prevent this is to set up a high priority VERTB interrupt that prevents running the lower priority interrupt servers in the chain by clearing the Z flag at the end.

04 July 2023, 13:11	#3
ross Defendit numerus Join Date: Mar 2017 Location: Crossing the Rubicon Age: 53 Posts: 4,474	Or the opposite, ie a very low priority VERTB, last in the chain, where you rewrite your COP2LC. This way you are transparent to the existing chain and don't affect it. Or set it to your copper list slightly before the COP2JMP call.

04 July 2023, 13:32	#4
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,516	Doing file io without vblank can cause problems for example if some 3rd party HD driver uses vblank mode CIA timers. Don't do that, please.

15 February 2024, 23:35	#5
KONEY OctaMED Music Composer Join Date: Jan 2009 Location: Venice - Italy Age: 49 Posts: 667	Sorry guys if I resume this but it looks like my problem... MainCopper won't jump to Copper2 because COP2LC value written by the CPU changes! Setting it from MainCopper would work but I can't do it because I'm building a series of frames and each Copper2 would update COP2LC with next Copper2 so that MainCopper would always jumps to the following Copper2. So how to fix it? Obviously I have no idea what "setting up a VERTB interrupt" means Thanks

16 February 2024, 08:58	#6
Wepl Moderator Join Date: Nov 2001 Location: Germany Posts: 866	Either use the OS or switch it off. Don't mix.

16 February 2024, 10:13	#7
KONEY OctaMED Music Composer Join Date: Jan 2009 Location: Venice - Italy Age: 49 Posts: 667	Well it turned out a VERTB interrupt was already in place since I'm using Photon's MiniWrapper. But I disabled it long ago because it would crash with some combinations of CPU/KS.

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