From: Eduardo TUDA Lorenzetti Pellini Newsgroups: comp.os.msdos.djgpp Subject: RE: Any comments about using RDTSC to sync code ? Date: Sun, 1 Apr 2001 19:29:06 -0400 Organization: Posted via Supernews, http://www.supernews.com Message-ID: <3AC9B77D@MailAndNews.com> X-InterChange-Posted-By: dochell AT MailAndNews DOT com Sender: Eduardo TUDA Lorenzetti Pellini X-EXP32-SerialNo: 50000000 Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Newsreader: InterChange (Hydra) News v3.61.08 X-Complaints-To: newsabuse AT supernews DOT com Lines: 45 To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Reply-To: djgpp AT delorie DOT com Thanks Tom ! >> So i think that the CPU clock may vary, but i don't know how much. > >Typically it's about 10%. My athlon 1200mhz runs at "supposedly" 1211mhz >according to various programs. You're right, I have a PIII 733 and an Athlon 800 with the same behaviour. Their clocks is almost the nominal clock (PIII reports 737 Mhz and Athlon 806 Mhz). What i'm asking is about the fluctuation of the clock along the time. I think that the PC clock generator don't have any stabilization method to compensate fluctuations on the crystal voltage/temperature that would change the computer clock rate. In this way, the computer sometimes runs at 800 Mhz... its clock will vary from, say, 799.3 Mhz to 810.5 Mhz... This kind of oscilation may create bad effects on my simulation... >Using RDTSC to sync programs is a bad idea since RDTSC may take a variable >amount of cycles to complete. On my tests i discovered that the RDTSC instruction takes from 12 to 20 clocks to complete. On an Athlon 800 Mhz this delay is a few nanoseconds... which i may forgive in my application... Thank you for all. Eduardo TUDA DocHell Lorenzetti Pellin PEA - Electrical Energy and Automation Department USP - Politechnical School of Sao Paulo University - BRAZIL http://www.pea.usp.br/~epellini --------------------------------- And if you have a time to loose, an open mind, and right to choose, would you care to take a look, or can you read me like a book... time's is allways on my side... --------------------------------- (Up the Irons !!!)