Date: Mon, 1 Jul 1996 16:19:03 -0400 From: Garrett Wollman <wollman@lcs.mit.edu> To: "Eric J. Schwertfeger" <ejs@bfd.com> Cc: questions@freebsd.org Subject: tickadj questions Message-ID: <9607012019.AA10857@halloran-eldar.lcs.mit.edu> In-Reply-To: <Pine.BSI.3.94.960624091642.8740B-100000@harlie.bfd.com> References: <Pine.BSI.3.94.960624091642.8740B-100000@harlie.bfd.com>
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<<On Mon, 24 Jun 1996 09:41:18 -0700 (PDT), "Eric J. Schwertfeger" <ejs@bfd.com> said: > 1) new_tick: as I understand it, this tells the system how many > microseconds should pass before it ticks the hz counter. Is this correct? > This gives the ability to correct to 100PPM, or about 8 seconds. No. It tells the system how many microseconds to add to the clock variable (called `time') when a timer tick occurs. > 2) new_tickadj: I'm not sure I understand this one. It obviously isn't > simply added to tick, otherwise there would be no point. I suspect that > it is added to the tick count once a second, for adjustments down to 1PPM. No. `tickadj' is the parameter which controls how fast the adjtime(2) system call is allowed to slew the clock. When adjusting in a negative direction, the clock code subtracts `tickadj' from `tick' before adding it to `time' on each clock tick. > 3) Does FreeBSD read or write the CMOS clock while running? I know with > SunOS 4.0, I have to turn this off. Actually, no. In SunOS 4.0, the operating system assumes that the CMOS clock is more accurate than the `time' variable and slaves the latter to the former (in a particularly ham-handed way). In FreeBSD, we are under no such delusions. However, when you reboot or halt the system under the control of reboot(2), the current value of `time' is written back into the CMOS clock (potentially with a timezone adjustment); there is a sysctl(8) MIB variable to disable this behavior. -GAWollman -- Garrett A. Wollman | Shashish is simple, it's discreet, it's brief. ... wollman@lcs.mit.edu | Shashish is the bonding of hearts in spite of distance. Opinions not those of| It is a bond more powerful than absence. We like people MIT, LCS, ANA, or NSA| who like Shashish. - Claude McKenzie + Florent Vollant
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