CPU Frequency

Leandro Jardim · 31 October 2011, 23:17

Hi Toni, I am playing with the cpu frequency slider a bit, trying to tune WinUAE to be able to measure 14.1 MHz in WhichAmiga, AIBB and SysInfo, but in my machine it shows 56 MHz...

[I am using as base the quickstart of A1200 cycle-exact with 4 MB of RAM.]

You already said some time ago that some cpu opcodes lacks time measurement (if so is called...). With base in this, I tuned WinUAE to 3.182298 MHz and I finally got 14.1 MHz in those tools...

But now I ask: benchmark tools like these can measure the correct speed of WinUAE? I heard from other sources that this type of measurement is very innacurate in virtual machines.

And the emulated chipset and the entire AmigaOS could not get overloaded with the slower emulated CPU clock, to end running slower than the real machine? I see the Workbench running very sluggish but I think it is the nature of the emulated machine, however I never played with AGA machines, so I could not assure this.

Thanks in advance!

Toni Wilen · 01 November 2011, 10:42

Do not try to match frequency that benchmark programs show, it isn't going to work. You will get slowdowns (missed vblanks) in games and demos because you halved the speed of CPU's memory accesses.

(Too) fast results are most likely due to usage of "slow" instructions like multiplication or division in a short loop that fits inside 68020's cache.

For example no one knows the exact MUL and DIV algorithm used in 68020 (68000 algoritm is known) so they are by design too quick in emulation just to be sure because always faster is more compatible than sometimes too slow.

Leandro Jardim · 02 November 2011, 22:18

Great explanation! Thanks!

31 October 2011, 23:17	#1
Leandro Jardim Registered User Join Date: Nov 2009 Location: Legoland Age: 45 Posts: 1,461	CPU Frequency Hi Toni, I am playing with the cpu frequency slider a bit, trying to tune WinUAE to be able to measure 14.1 MHz in WhichAmiga, AIBB and SysInfo, but in my machine it shows 56 MHz... [I am using as base the quickstart of A1200 cycle-exact with 4 MB of RAM.] You already said some time ago that some cpu opcodes lacks time measurement (if so is called...). With base in this, I tuned WinUAE to 3.182298 MHz and I finally got 14.1 MHz in those tools... But now I ask: benchmark tools like these can measure the correct speed of WinUAE? I heard from other sources that this type of measurement is very innacurate in virtual machines. And the emulated chipset and the entire AmigaOS could not get overloaded with the slower emulated CPU clock, to end running slower than the real machine? I see the Workbench running very sluggish but I think it is the nature of the emulated machine, however I never played with AGA machines, so I could not assure this. Thanks in advance! Last edited by Leandro Jardim; 31 October 2011 at 23:34.

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01 November 2011, 10:42	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,515	Do not try to match frequency that benchmark programs show, it isn't going to work. You will get slowdowns (missed vblanks) in games and demos because you halved the speed of CPU's memory accesses. (Too) fast results are most likely due to usage of "slow" instructions like multiplication or division in a short loop that fits inside 68020's cache. For example no one knows the exact MUL and DIV algorithm used in 68020 (68000 algoritm is known) so they are by design too quick in emulation just to be sure because always faster is more compatible than sometimes too slow.

02 November 2011, 22:18	#3
Leandro Jardim Registered User Join Date: Nov 2009 Location: Legoland Age: 45 Posts: 1,461	Great explanation! Thanks!

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