Re: Linux timekeeping plans
Stefan Monnier (monnier+lists/linux/kernel@tequila.cs.yale.edu)
Fri, 04 Dec 1998 14:15:25 -0500
Kris Karas wrote:
> Stefan Monnier wrote:
> > I must say (as an NTP user) that I don't understand: why don't you just
> > allow xntpd to use the RTC as a local clock and let xntpd slave ths system
> > clock with it ?
> The RTC has a precision of 1 second, if memory serves, even though it can
> generate interrupts more rapidly. In order for the system to derive more
> precision, it must do what hwclock(8) does - watch carefully for the transition
> of the seconds digit, and set the kernel's fractional-seconds portion of the
> time to zero. This is inherently costly to do. If memory also serves, the RTC
> is a slow device - reading it may take a microsecond or more more per byte.
Indeed, which is why I want to keep the RTC support separate (exporting it
for xntpd's use) so that I can run with a sane system (not using the RTC
but a remote time server). To make "good" use of the RTC, you'd probably
be better off to use it as a PPS source.
Stefan
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