Cycle exact and real amiga speed

zygzak · 18 April 2014, 10:57

Hello. There is option in newer WinUAE versions which allows to change the CPU speed in cycle exact mode as a factor for original Amiga speed. On my real A500, F-15 Strike Eagle 2 game were always running slow like hell - compared to PC 286/386 version. A500 had 7.14 MHz clock, and I always thought that increasing the clock or changing CPU unit could make the game run much faster.
In WinUAE, the game runs similar slow so I tried to increase cycle exact cpu speed to 14, 28, 60 or 120 (1x corresponds to 3.5MHz). It has affected for the speed of animation in opening screen (where II and plane are rotating) but in game the speed is practicaly the same. Does it mean that even changing CPU/increasing clock in the real Amiga 500 wouldn't have any influence on speed of this game?

Toni Wilen · 18 April 2014, 14:24

Yes, increasing clock rate won't help much 68000 based Amigas. CPU does not have any caches which means CPU is 90%+ of time only waiting for memory (and in worst case chipset DMA is also stealing many CPU memory cycles), practically only instructions that can run a lot faster are long shifts, multiplication and division.

Exceptions are accelerators like Supraturbo that have small cache memory.

Real fast ram will also help but unfortunately most old games only use chip ram and/or slow ram.

18 April 2014, 10:57	#1
zygzak Registered User Join Date: Oct 2009 Location: Poland Posts: 51	Cycle exact and real amiga speed Hello. There is option in newer WinUAE versions which allows to change the CPU speed in cycle exact mode as a factor for original Amiga speed. On my real A500, F-15 Strike Eagle 2 game were always running slow like hell - compared to PC 286/386 version. A500 had 7.14 MHz clock, and I always thought that increasing the clock or changing CPU unit could make the game run much faster. In WinUAE, the game runs similar slow so I tried to increase cycle exact cpu speed to 14, 28, 60 or 120 (1x corresponds to 3.5MHz). It has affected for the speed of animation in opening screen (where II and plane are rotating) but in game the speed is practicaly the same. Does it mean that even changing CPU/increasing clock in the real Amiga 500 wouldn't have any influence on speed of this game?

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18 April 2014, 14:24	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,506	Yes, increasing clock rate won't help much 68000 based Amigas. CPU does not have any caches which means CPU is 90%+ of time only waiting for memory (and in worst case chipset DMA is also stealing many CPU memory cycles), practically only instructions that can run a lot faster are long shifts, multiplication and division. Exceptions are accelerators like Supraturbo that have small cache memory. Real fast ram will also help but unfortunately most old games only use chip ram and/or slow ram.

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