Blitter Priority - Blthog

Asman · 11 December 2016, 21:40

I am trying to better understand why blitter priority (blthog or blitter nasty bit) must be not set if we want to be compatible with other machines then a500.

I read in WHDLoad documentation http://www.whdload.de/docs/en/snoop.html

"The Blitter Priority can cause problems on some hardware configuration in conjunction with large blitter operations (all channels used)."

I'm very curious on which configuration blthog can casue problems and what problems ? Any ideas ?

Toni Wilen · 12 December 2016, 19:58

I think it is sort of misunderstanding and more related to some accelerators having slow chip ram access speed. If blitter does not steal all cycles, CPU at least gets some extra cycles to compensate for lost cycles due to slow chipram access speed.

Wepl · 12 December 2016, 20:32

I had hang situations with the initial decoding in Arkanoid and also some reports from users where games did not work with blthog on (as it was in the original game setup).
I don't know reasons behind but assume that there are hardware constellations which have problems with that.

Asman · 12 December 2016, 21:26

Thanks a lot Toni and Wepl for answers.

11 December 2016, 21:40	#1
Asman 68k Join Date: Sep 2005 Location: Somewhere Posts: 829	Blitter Priority - Blthog I am trying to better understand why blitter priority (blthog or blitter nasty bit) must be not set if we want to be compatible with other machines then a500. I read in WHDLoad documentation http://www.whdload.de/docs/en/snoop.html "The Blitter Priority can cause problems on some hardware configuration in conjunction with large blitter operations (all channels used)." I'm very curious on which configuration blthog can casue problems and what problems ? Any ideas ?

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12 December 2016, 19:58	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,573	I think it is sort of misunderstanding and more related to some accelerators having slow chip ram access speed. If blitter does not steal all cycles, CPU at least gets some extra cycles to compensate for lost cycles due to slow chipram access speed.

12 December 2016, 20:32	#3
Wepl Moderator Join Date: Nov 2001 Location: Germany Posts: 876	I had hang situations with the initial decoding in Arkanoid and also some reports from users where games did not work with blthog on (as it was in the original game setup). I don't know reasons behind but assume that there are hardware constellations which have problems with that.

12 December 2016, 21:26	#4
Asman 68k Join Date: Sep 2005 Location: Somewhere Posts: 829	Thanks a lot Toni and Wepl for answers.

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