[USRP-users] RFNoC TX Channel Alignment

Reggie Wilcox rwilcox at haystack.mit.edu
Thu Nov 9 17:36:40 EST 2017


Hello,

I am trying to use Gnuradio to interface to an X300 running an RFNoC image.
I set up my initial configuration to transmit the same signal to both TX
channels using the GUI, but am having trouble aligning the two channels in
time. Each time I run the code, there is a different time offset between
the two channels. I suspect this is based off of the arrival time of the
packets to start the stream for each channel and that I need to control the
start time for both channels to fix this, but have been unable to find any
documentation or examples on how to set this up.

Briefly, I have a square wave generator going into a 2-port RFNoC: DmaFifo
block. Each output of the fifo drives a RFNoC: DUC then a RFNoC: Radio
block. A screenshot of the setup is attached. I have been attempting to
then set the start of of each radio to the same value, but my approach
doesn't affect the start time of transmission. I tried inserting in the
python code:
self.uhd_rfnoc_streamer_radio_0.set_time_next_pps(uhd.time_spec(0));
self.uhd_rfnoc_streamer_radio_1.set_time_next_pps(uhd.time_spec(0));
self.uhd_rfnoc_streamer_radio_0.set_start_time(uhd.time_spec(15));
self.uhd_rfnoc_streamer_radio_1.set_start_time(uhd.time_spec(15));

However, the transmission starts just after I run the script, instead of
waiting 15s, indicating that my code has no effect.

Any suggestions on how to set configure the X300 so its TX channels are
aligned?

Thanks for your help,

~Reggie
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