Re: [Discuss-gnuradio] Viewing timestamps using USRP2

MarcW wrote:
> Thanks for your help Doug. I thought I knew which bits to monitor which
> contained the timestamp but now im not sure! The packets received seem very
> large. I have included a screenprint of one below. Please could you tell me
> which bits are the timestamp in this packet?
> The data appears to start from line 0020 but every other 32 bits are either
> ff or 00.
> Do we add the sync_every_pps() to txrc.c immediately before the while loop?
>
>
Which version of gnuradio are you running? If you're using the
usrp2-vrt git branch, the frame format has changed dramatically. If
you're using the released code (or the master branch from git) the frame
structure is (IIRC) defined in
usrp2/firmware/include/usrp2_eth_packet.h. There's the standard ethernet
header (dst, src, ethertype), a short 'transport' header (some flags,
sequence number, etc.), and the 'fixed' header which has some more
flags, and the 32-bit timestamp. The VRT format has a much longer
header, and includes a seconds count and a fractional seconds count.
You don't need to call sync_every_pps() in the firmware (do you really
want to reset the clock every PPS?). The host can send the command to
sync_*_pps() when setting up the connection to the USRP2. For example,
in rx_streaming_samples, call u2->sync_to_pps() (or sync_every_pps() if
you really want that) before calling u2->start_rx_streaming. Then you
can have the copy handler print out the timestamp from each frame
received by the USRP2. In the VRT branch I believe there is already an
example application that prints out the timestamp from received frames.
Doug

--
Douglas Geiger
Code 5545
U.S. Naval Research Laboratory
Washington, DC 20375
(202) 767-9048
douglas.geiger@nrl.navy.mil

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