On 04/08/2013 04:45 PM, Jordan Otomo wrote:
Hi,
I have a packet-based application where it would be useful to know exactly when
each packet has been successfully radiated by the USRP (N200). It seems that
UHD and gr-uhd already provide similar functionality for receiving asynchronous
messages when a burst has been successfully transmitted (EVENT_CODE_BURST_ACK).
However, in my application, I'm transmitting continuously and don't use
end_of_burst tags. Would it be possible for the USRP to post messages to the
event queue when it has transmitted a sample with a generic tag attached? If
not, will I experience an interruption of my signal or any latency if I insert
end_of_burst tags into my continuous stream of samples? Your advice is greatly
appreciated.
I'm a bit confused by what you mean when you say you're transmitting
continuously in a packet-based application. Are the packets back-to-back
in your sample stream? Or are you stuffing a bunch of zero samples in
between packets? That isn't the cleanest way to do it. It would be
better to use start-of-burst ("tx_sob") and end-of-burst ("tx_eob") tags
if you're using gnuradio.
Gnuradio end-of-burst tags will signal UHD firmware to bring down the TX
chain. The tag gets converted into a flag in a metadata struct. This
struct is sent with an 1-sample buffer of samples when send(...) is
called in gr_uhd_usrp_sink. (See line 376 and thereabouts here:
http://gnuradio.org/cgit/gnuradio.git/tree/gr-uhd/lib/gr_uhd_usrp_sink.cc).
Thanks!
Jordan
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Hope this helps!
--sean
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