Meaning of "CPU Compatible" option?

rsn8887 · 01 October 2019, 00:04

Sonninnos and I are trying to understand some UAE options better to improve the usability of Retroarch PUAE core.

What is the meaning and speed impact of the CPU compatible option?

How does it interact with Cycle Exact?

Could we force CPU compatible ON whenever cycle exact is ON and OFF whenever cycle exact is OFF?

Or would that remove an important configuration option for the users?

Toni Wilen · 01 October 2019, 08:45

More compatible:

68000 and 68010: adds emulation of prefetch pipeline and data address error exceptions (without more compatible only jump to odd address causes address error exception). Prefetch is needed by many copy protections and self-modifying code tricks.

68020+: adds prefetch and instruction cache emulation.

Cycle-exact = more compatible + cycle-exact specific new features enabled. Cycle-exact is not possible without prefetch emulation. (Instruction internal memory access order would change which would change timing)

Cycle-exact is much more CPU heavy than more compatible.

rsn8887 · 01 October 2019, 18:37

Awesome, thanks for the detailed explanation.

sonninnos · 02 October 2019, 21:42

Might you Toni also have any idea how come "More compatible" can in fact be less compatible? In IK+ the sound effects go missing only when compatible alone is enabled. Cycle exact and "uncompatible" are fine. Can that be just an isolated incident?

Jättikiitokset kaikesta ja terkut Lahest!

Toni Wilen · 03 October 2019, 16:30

IK+ (and Warhead I think) sound issue is timing related side-effect (audio interrupt). Both games have bad audio code that only accidentally works.

Timing related problems are always "undefined" except in cycle-exact mode

01 October 2019, 00:04	#1
rsn8887 Registered User Join Date: Oct 2006 Location: USA Posts: 1,058	Meaning of "CPU Compatible" option? Sonninnos and I are trying to understand some UAE options better to improve the usability of Retroarch PUAE core. What is the meaning and speed impact of the CPU compatible option? How does it interact with Cycle Exact? Could we force CPU compatible ON whenever cycle exact is ON and OFF whenever cycle exact is OFF? Or would that remove an important configuration option for the users?

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01 October 2019, 08:45	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,518	More compatible: 68000 and 68010: adds emulation of prefetch pipeline and data address error exceptions (without more compatible only jump to odd address causes address error exception). Prefetch is needed by many copy protections and self-modifying code tricks. 68020+: adds prefetch and instruction cache emulation. Cycle-exact = more compatible + cycle-exact specific new features enabled. Cycle-exact is not possible without prefetch emulation. (Instruction internal memory access order would change which would change timing) Cycle-exact is much more CPU heavy than more compatible.

01 October 2019, 18:37	#3
rsn8887 Registered User Join Date: Oct 2006 Location: USA Posts: 1,058	Awesome, thanks for the detailed explanation.

02 October 2019, 21:42	#4
sonninnos Commodork Join Date: Nov 2018 Location: Finland Posts: 83	Might you Toni also have any idea how come "More compatible" can in fact be less compatible? In IK+ the sound effects go missing only when compatible alone is enabled. Cycle exact and "uncompatible" are fine. Can that be just an isolated incident? Jättikiitokset kaikesta ja terkut Lahest!

03 October 2019, 16:30	#5
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,518	IK+ (and Warhead I think) sound issue is timing related side-effect (audio interrupt). Both games have bad audio code that only accidentally works. Timing related problems are always "undefined" except in cycle-exact mode

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