Does "Cycle-exact" do nothing with the AGA chipset?

fmcpma · 22 October 2006, 17:43

I ask this because, in the default configs ("models") selected in "Quickstart", those using AGA have this setting turned off and those using OCS have it turned on.

Thanks for any answers.

Npl · 24 October 2006, 23:16

Cycle-exact is only effective with OCS & 68000

rgen · 25 October 2006, 11:27

With OCS you had a 7.xx MHz CPU with a 7.xx MHz Chipset and instructions took a specific duration, which some programmers expected but with AGA, machines were delivered with different CPUs, with different MHz and even for a single CPU at a specific clock, a instruction have no regular duration anymore as all the CPUs have cache(s) which influence timing.

Toni Wilen · 25 October 2006, 11:33

Cycle-exact checkbox does affect AGA timing but it does not make it cycle-exact (far from it..), it only tweaks blitter timing which can fix some problems and it will cause new problems. It is basically only for testing if cpu is 68010 or higher.

btw, loading new configuration will always untick it if selected cpu is 68010 or higher.

rsn8887 · 25 October 2006, 17:30

Am I guessing right that this is the reason why "super stardust aga" is so hard to emulate?

fmcpma · 26 October 2006, 00:15

I've noticed "cycle-exact" fixes (for me) the following AGA games: Alfred Chicken, Skeleton Krew and Worms -- Director's Cut...

Is there really no cycle-exactness in a real A1200?

rgen · 26 October 2006, 02:14

There is cycle exactness within the chipset; chipset <-> chip ram and chipset/chip ram cycles <-> cpu.

The thing that is not possible anymore is to predict the number of instructions the cpu worked on in relation to the chipset timing as AGA machines were built with different cpus whereas OCS had a fixed timing to 68000's instructions as well.

Toni Wilen · 26 October 2006, 08:12

Biggest problem is 68020+'s cache.

TikTok · 26 October 2006, 09:52

Which, I'm guessing, is why turning off the CPU caches in the boot menu used to fix some of those older OCS games, right?

rgen · 26 October 2006, 12:59

Quote:

Originally Posted by TikTok

Which, I'm guessing, is why turning off the CPU caches in the boot menu used to fix some of those older OCS games, right?

Turning off the caches only fixes the problem of selfmodifying code, the cpu itselfs are still faster than the 68000 (A1200's cpu have a double clock rate, a 32 bit memory interface and internal optimizations compared to A500's 68000).

Toni Wilen · 26 October 2006, 13:11

It can fix _some_ self-modifying code problems. 68020 has much longer and different prefetch system than 68000. Disabled cache can also make it much slower, especially if running short loops in chip memory.

22 October 2006, 17:43	#1
fmcpma Banned Join Date: Aug 2005 Location: Portugal / Porto Age: 59 Posts: 62	Does "Cycle-exact" do nothing with the AGA chipset? I ask this because, in the default configs ("models") selected in "Quickstart", those using AGA have this setting turned off and those using OCS have it turned on. Thanks for any answers.

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24 October 2006, 23:16	#2
Npl Registered User Join Date: Aug 2004 Location: Vienna / Austria Age: 44 Posts: 257	Cycle-exact is only effective with OCS & 68000

25 October 2006, 11:27	#3
rgen Registered User Join Date: Mar 2002 Location: Aachen/Germany Age: 46 Posts: 190	With OCS you had a 7.xx MHz CPU with a 7.xx MHz Chipset and instructions took a specific duration, which some programmers expected but with AGA, machines were delivered with different CPUs, with different MHz and even for a single CPU at a specific clock, a instruction have no regular duration anymore as all the CPUs have cache(s) which influence timing.

25 October 2006, 11:33	#4
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,502	Cycle-exact checkbox does affect AGA timing but it does not make it cycle-exact (far from it..), it only tweaks blitter timing which can fix some problems and it will cause new problems. It is basically only for testing if cpu is 68010 or higher. btw, loading new configuration will always untick it if selected cpu is 68010 or higher.

25 October 2006, 17:30	#5
rsn8887 Registered User Join Date: Oct 2006 Location: USA Posts: 1,058	Am I guessing right that this is the reason why "super stardust aga" is so hard to emulate?

26 October 2006, 00:15	#6
fmcpma Banned Join Date: Aug 2005 Location: Portugal / Porto Age: 59 Posts: 62	I've noticed "cycle-exact" fixes (for me) the following AGA games: Alfred Chicken, Skeleton Krew and Worms -- Director's Cut... Is there really no cycle-exactness in a real A1200?

26 October 2006, 02:14	#7
rgen Registered User Join Date: Mar 2002 Location: Aachen/Germany Age: 46 Posts: 190	There is cycle exactness within the chipset; chipset <-> chip ram and chipset/chip ram cycles <-> cpu. The thing that is not possible anymore is to predict the number of instructions the cpu worked on in relation to the chipset timing as AGA machines were built with different cpus whereas OCS had a fixed timing to 68000's instructions as well.

26 October 2006, 08:12	#8
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,502	Biggest problem is 68020+'s cache.

26 October 2006, 09:52	#9
TikTok Registered User Join Date: Jul 2001 Location: Malayasia Age: 43 Posts: 657	Which, I'm guessing, is why turning off the CPU caches in the boot menu used to fix some of those older OCS games, right?

26 October 2006, 13:11	#11
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,502	It can fix _some_ self-modifying code problems. 68020 has much longer and different prefetch system than 68000. Disabled cache can also make it much slower, especially if running short loops in chip memory.

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