Re: NSLU2 clock drift
On May 18, 2007, at 6:00 AM, Marcus Better wrote:
my NSLU2 (266 MHz) has a problem with timekeeping. I run ntp, but
help - the clock drifts at least fifteen minutes a day. Did I miss
something obvious? My kernel is 2.6.20-1-ixp4xx.
If you're running Debian, you may be able to use the "tickadj"
command at boot time to fudge the value of the kernel variable
"tick" (the number of microseconds added to the system clock every 1/
HZ seconds when the RTC interrupt occurs).
You should read the man page for "tickadj", but it's mostly all about
stuff that doesn't matter here. The important part is that you can
modify "tick". Normally (If HZ is set to it's standard value of 100)
tick is 10000 (ten thousand microseconds per hundredth of a second).
So, making tick larger, say for example, 10020, will make the system
clock run, in this example, 2 parts per thousand ("ppt") faster.
So, if your system clock is 15 minutes slow after a day of free
running with NTP turned off (NTP will really confuse things if it's
turned on during this part of the experiment) It's running 15/
(24*60) = 10.4 ppt (or 1.04 percent) slow, and you should set tick to
If the system keeps reasonable time (drift of less than 0.5 ppt) with
this adjustment, you can safely turn on NTP again, and it will then
keep time as well as your NTP server.