On 19/04/2015 09:42, Pratik Pawar wrote:
Hi All,
I have one strange question about chrony.
I am using chrony to keep embedded board system time
in sync. When GPS receiver is connected to board, It can
able to sync system time with very negligible deviation.
The reference clock for chrony are PPS & SHM.
Whenever GPS receiver got new time stamp,
application log that value into*a *file as well as Same
timestamp is being given to SHM. GPS receiver is sending
updated time stamp at every 200ms.
I want to simulate same think. For this I am reading
logged timestamp from**file & sending it through UDP
packet at 200ms interval using another application.
Embedded board receive that UDP packet extract
timestamp information & write it into SHM.
With this approach chrony able to get SHM data & sync
system time. But I am getting lots of deviation. PPS is
disable only SHM is enable for this chrony.
Can any one tell me a better approach or previous
experience to achieve this.
You can't "simulate" a time reference source. If it were any
good then it would be an actual time reference source.
Having a list of timestamps in a file is completely useless;
presumably you're sleeping for 200ms in that "another
application" and now that operation, as well as the delay in
reading from the file and sending the packet over UDP, is
your new timebase. That is going to be orders of magnitude
less stable than just using the existing, unreferenced
system clock in the first place (which is driven by an
oscillator, not by entirely unpredictable mechanical
movements, memory congestion, CPU congestion, network
conditions...).
You should rethink your goal here.
Hope that helps
Tom
