On Wed, Apr 14, 2010 at 11:55:54PM +0000, unruh wrote: > On 2010-04-14, lhommedumatch <[email protected]> wrote: > > The ntpgmtaceb (this clock loses 1.10e-11second every second => ie 8.6 > > 10e-7s each days) is providing zda+pps, I have worked on using PPS > > with LinuxPPS. > > But I need to patch the kernel. I'm using CentOS 5.4 => linux2.6.18. > > Why do you need to patch the kernel? Just use shmpps or gpsd to deliver > the PPS time to ntpd to discipline the clock. Now, that may only give > you 1usec accuracy, instead of 1/2usec, but since discussion was about > ms, that should not be the problem
Userspace timestamps may decrease the accuracy by more than just 0.5 us. When I compare kernel timestamps and timestamps from gpsd, there is a 20-40us difference, even when the gpsd process has real time priority and the machine is otherwise idle. Of course, for 1ms requirement this doesn't matter. -- Miroslav Lichvar _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
