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When there are several machines involved, how are timestamps created? It looks like to me that they're being generated by each machine's individual time, so if one machine is out of sync with another than all the messages will be in the past or the future. Is this actually the case or am I missing something, and how do people deal with this limitation?
You're correct, they just use the system's current time. The typical way I've seen to synchronize time across computers is to use Chrony. With Ubuntu, you should be able to just run apt-get install chrony.
Here are some resources I've found on a quick search:
http://answers.ros.org/question/2140/chrony-configuration-and-limitations
http://pr2support.willowgarage.com/wiki/PR2%20Manual/Chapter13#Clock_Synchronization
The important information is that your ROS system computers are tightly coupled in time, but loosely tied to the outside world's time.
If anyone requires, the link for: http://pr2support.willowgarage.com/wi... has been changed to: https://www.clearpathrobotics.com/ass... since PR2 has changed hands from Willow Garage to Clear Path Robotics
You're exactly right, the timestamps are generated from each machine's individual clock. So it's very important to keep all clocks synchronized. On the PR2 robot (which contains two machines) we use Chrony.
Asked: 2011-10-17 06:56:41 -0500
Seen: 13,740 times
Last updated: Oct 17 '11
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