[Discuss-gnuradio] Timestamps, data rates

[Douglas Geiger]

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 I'm running some experiments with my two USRP2's - as I want to get
synchronized samples out of them. I have the clock's locked to my
external 10Mhz, and they sync_to_pps correctly (i.e. the timestamp
resets on the next PPS).
 However, the difference between timestamps from the two USRP2's does
not seem to be a constant at low data rates: they are constant between
subsequent received frames (i.e. USRP2 A vs. USRP2 B) - but each time I
start my application, or even if I send sync_to_pps commands while
streaming, the difference changes. I'm trying to figure out if this is
due to some non-deterministic timing on the USRP2, or some other source.
 At higher data rates (e.g. decimation <= 16), the difference between
timestamps from the two USRP2's gets more erratic, and tends to
fluctuate (quite wildly down at -d 4).
 My plan has been to setup buffers to align samples based on timestamp -
 but with such variations it looks to me like it could be quite
difficult to implement. Or at the very least, I'd need very large
buffers, and could end up needing/wanting to change their size often.
 Any suggestions on how to best deal with this? Should I be looking into
the USRP2 firmware code to try to get some more predictable behavior out
of it?
 Thanks,
  Doug

- --
Doug Geiger
Research Assistant
Communications and Signal Processing Lab
Oklahoma State University
http://cspl.okstate.edu
address@hidden
address@hidden
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