From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <366D8CF9.55DF77F9@jlc.net> Date: Tue, 08 Dec 1998 15:32:57 -0500 From: Dan Malek MIME-Version: 1.0 To: Cort Dougan CC: Troy Benjegerdes , linuxppc-dev@lists.linuxppc.org Subject: Re: PReP RTC vs Decrementer accuracy... References: Content-Type: text/plain; charset=us-ascii Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: Cort Dougan wrote: > Right, the rtc is probably more accurate over a long period of time... Nope, not even close. If you convert rtc drift specifications and processor oscillator drift specifications to a common reference (like PPM) you will see processor oscillators are significantly better than any rtc. Of course, running PLLs with high multipliers, like 32kHz up to 50 Mhz will cause wide variations, but over a long period of time they will they will be more accurate time keepers. > ....... The drift should be corrected by > a time daemon. Yes, but sometimes they are the cause of the problem, so check that too. If the PPC decrementer does not appear to be keeping time correctly, first ask how often the system is restarted. Since the time is initially set from the rtc, if that is out of whack (and many are) and you reboot frequently, the system time will drift from a wall clock in a hurry. The decrementer should keep time very accurately from system start up to shut down. If it isn't we have some fixing to do. I believe the design to be correct, but the implementation may be a little flawed. -- Dan [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. To unsubscribe from linuxppc-dev, send ]] [[ the message 'unsubscribe' to linuxppc-dev-request@lists.linuxppc.org ]]