[ntp:questions] Re: Advice on sync clock between cluster of linux v2.6 to +-1us
spam at nospam.blueyonder.co.uk
Wed Jan 12 20:12:12 UTC 2005
Thank you Brad, Richard and Helmut for your prompt replies.
Originally I was thinking a connection setup similar to would suffice:
External clock Reference --> Master Node --> Other computers nodes via
I did not realise that inherent delays as Richard mention in Ethernet
would be the best achievable accuracy. Maybe a setup below would be more
External Reference --> All computer nodes using a signal booster/splitter
Even still, I doubt this would guarantee the accuracy between the nodes
of +- 1 microsecond.
Helmut - When I mentioned 'cluster', I meant a group (< 10) of computers
connected by Ethernet.
I have been given this more thought today and suspect I am approaching
The problem resolves event timing in a test rig. Each computer node are
part of the test rig and basically act as an I/O interface to the
system-under-test. Each node would be given a list of event instructions
and the time stamp when the event should be triggered. This time stamp
would be relative to the start of the test and hence my original
statement that "actual time is not required".
Thinking aloud - Another solution could be using the processor local
clock. I believe all 386 processors have them and assume their drift
would not be excessive. (Anyone have statistics on this?) Each node
loads their instructions and wait for the master node to send a start
signal. The master node could send a Ethernet broadcast 'start' packet
(assuming the network infrastructure sends broadcast data to all ports
at the same time). On receipt, each client node records their local
clock time stamp as the "start time" and immediately run the test. All
the events in the test would be triggered relative to this "start time".
I wouldn't like to say how accurate this is but willing to take opinions
or better solutions.
All the best,
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