discussion forum message Name: unknown Date: September 30, 2003 at 19:39:04 Subject: Re: Question about RDTSC programming In Reply To: Re: Question about RDTSC programming by unknown on September 30, 2003 at 16:15:05 Text: || To calculate the CPU speed you need to use the 8254 timer (ports 40h-43h) || It has a resolution of 838ns and is the same on all PCs and has been so || since the original IBM PC. Depending on what you're doing you might want || to just use the 8254 timer in your game engine. || || The link points to Intel's CPUID document which includes code to calculate || the CPU speed. Getting the bus speed and multiplier involves reading MSRs || and is different between processor families. You shouldn't really need that || info anyway in a game engine. || | | Hey thanks for getting back to me, I will look into that doc. Ya I shouldnt need to access the MSR but i thought I could get the speed by Bus x multiplier but if this way works thats great. How accurate is it? Thanks | Using the 8254 timer and RDTSC to time a small sequence of code is very accurate. You can accurately calculate CPU speed to at least 0.1 Mhz, probably 0.01 Mhz. post a followup message (Be nice... or be blocked. Be technical... or be erased.) Name: optional link title: eMail: optional link URL: Subject: optional image URL:   Insert line breaks by hand when only about one inch remains at the right side. Otherwise your message will be unreadable. Text: ||| To calculate the CPU speed you need to use the 8254 timer (ports 40h-43h) ||| It has a resolution of 838ns and is the same on all PCs and has been so ||| since the original IBM PC. Depending on what you're doing you might want ||| to just use the 8254 timer in your game engine. ||| ||| The link points to Intel's CPUID document which includes code to calculate ||| the CPU speed. Getting the bus speed and multiplier involves reading MSRs ||| and is different between processor families. You shouldn't really need that ||| info anyway in a game engine. ||| || || Hey thanks for getting back to me, I will look into that doc. Ya I shouldnt need to access the MSR but i thought I could get the speed by Bus x multiplier but if this way works thats great. How accurate is it? Thanks || | Using the 8254 timer and RDTSC to time a small sequence of code is very | accurate. You can accurately calculate CPU speed to at least 0.1 Mhz, | probably 0.01 Mhz. |     Note: The above eMail form fields may look unaligned if you are using a browser other than Netscape Navigator version 3.0. currently posted followup messages (You may have to press the RELOAD button of your browser.) Re: Question about RDTSC programming by unknown, 01:31:28 2003/10/01 (12) Re: Question about RDTSC programming by unknown, 11:33:18 2003/10/01 (9) Re: Question about RDTSC programming by unknown, 14:56:57 2003/10/01 (8) FDA by Peter, 20:48:50 2003/11/19 (1) Re: FDA by bali, 22:48:27 2003/12/17 (0) Re: Question about RDTSC programming by unknown, 16:46:38 2003/10/01 (5) FDA by Peter, 20:48:52 2003/11/19 (2) bali by bali, 23:24:05 2003/12/18 (0) bali by bali, 02:29:36 2003/12/18 (0) Re: Question about RDTSC programming by unknown, 04:57:14 2003/10/02 (1) FDA by Peter, 20:56:06 2003/11/19 (0) Re: Question about RDTSC programming by fcpuid, 06:12:55 2003/10/01 (1) Re: Question about RDTSC programming by Christian Ludloff, 07:19:09 2003/10/01 (0)