[ros-users] Another question about policy based synchronizer
Aditya Gadre
agadre at vt.edu
Mon Oct 18 16:28:23 UTC 2010
I have a working test code for policy based (approximate time)
synchronizer in which one node publishes two data messages and the other
node runs a synchronizer. One message is published at 1Hz and the other
at 0.5Hz. For each message, I increment the relevant sequence number in
the header. However, when these messages are received by the node
running the policy based synchronizer, the sequence numbers are off by
1, although the time stamps match perfectly.
For example, following output shows a simple run -
Publisher log:
[ INFO] [1287418571.114515026]: Starting
test_policy_synchronizer_publisher node.
[ INFO] [1287418571.122496486]: Publishing AHRS data: time =
1287418571.122447, seq = 1
[ INFO] [1287418572.122643642]: Publishing AHRS data: time =
1287418572.122516, seq = 2
[ INFO] [1287418572.122956042]: Publishing Alasca data: time =
1287418572.122883, seq = 1
[ INFO] [1287418573.122685477]: Publishing AHRS data: time =
1287418573.122559, seq = 3
[ INFO] [1287418574.122935718]: Publishing AHRS data: time =
1287418574.122809, seq = 4
[ INFO] [1287418574.123219204]: Publishing Alasca data: time =
1287418574.123158, seq = 2
[ INFO] [1287418581.122753362]: Shutting down
test_policy_synchronizer_publisher node.
Synchronizer node log:
[ INFO] [1287418573.123472169]: ----------
[ INFO] [1287418573.123744969]: Received message set
[ INFO] [1287418573.123947997]: AHRS: timestamp = 1287418572.122516, seq = 1
[ INFO] [1287418573.124106258]: Alasca: timestamp = 1287418572.122883,
seq = 0
[ INFO] [1287418575.122839197]: ----------
[ INFO] [1287418575.122900518]: Received message set
[ INFO] [1287418575.122951782]: AHRS: timestamp = 1287418574.122809, seq = 3
[ INFO] [1287418575.123003883]: Alasca: timestamp = 1287418574.123158,
seq = 1
Comparing time stamps of sent and received messages, I see that the
sequence numbers in the synchronizer node are off by 1 (if sent message
seq = 3 then received message seq = 2). I am not sure why this
discrepancy is popping up. I would appreciate any help in this regard! I
have attached source code for both nodes.
Thank you.
- Aditya
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