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-   -   Meaning of "CPU Compatible" option? (http://eab.abime.net/showthread.php?t=99011)

rsn8887 01 October 2019 01:04

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?

Toni Wilen 01 October 2019 09:45

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 19:37

Awesome, thanks for the detailed explanation.

sonninnos 02 October 2019 22:42

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?

J├Ąttikiitokset kaikesta ja terkut Lahest!

Toni Wilen 03 October 2019 17:30

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 :)


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