No packet reception when using uhd_tune_request

Hi All,

I have a couple of questions this time.

  1. I have a setup in which I transmit gmsk packets from a tx node which
    are then received successfuly at an rx node (both nodes are USRP N200
    radios and are being operated by GRC). However, when I turn off the
    cordic at two nodes by putting this line in uhd usrp sink at tx node and
    in uhd usrp source at rx node, I do not receive any packets at all at rx
    node.
    uhd.tune_request(915e6,
    dsp_freq=0,dsp_freq_policy=uhd.tune_request.POLICY_MANUAL)
    I have verified (by means of get_center_frequency() method) that the two
    nodes in this case are set to the same center frequency which is 914.285
    MHz, so, there is no center freq mismatch between tx and rx nodes. In
    this case, I see some underflows at tx node and if I put a scope at rx
    node to see the raw received samples, then I see that the samples are
    not being received continuously (i.e., I see received gmsk samples for a
    few seconds, then noise samples for next few seconds and so on) even
    though the tx node is sending packets back-to-back.

  2. Previously, the frequency of DUC/DDC cordic, target frequency, actual
    frequency used to be printed out while running any flow-graph involving
    usrp sink/source but it is not the case anymore. What is the easiest way
    to print all this info while within GRC?

Thanks,
Yu.

On 10/31/2012 01:10 PM, Zing Yu wrote:

dsp_freq=0,dsp_freq_policy=uhd.tune_request.POLICY_MANUAL) I have
verified (by means of get_center_frequency() method) that the two
nodes in this case are set to the same center frequency which is
914.285 MHz, so, there is no center freq mismatch between tx and rx
nodes. In this case, I see some underflows at tx node and if I put a
scope at rx node to see the raw received samples, then I see that the
samples are not being received continuously (i.e., I see received
gmsk samples for a few seconds, then noise samples for next few
seconds and so on) even though the tx node is sending packets
back-to-back.

Every thing you are doing sounds correct.

Am am a bit confused about underflows. Are you saying that the transmit
underflows, but only with the special tune request? Normally it does
not?

I suggest that you check that daguhterboard LO is locked after the tune.
print usrp_source.get_rx_sensor(“lo_locked”).to_bool()

What daughterboard are you using?

  1. Previously, the frequency of DUC/DDC cordic, target frequency,
    actual frequency used to be printed out while running any flow-graph
    involving usrp sink/source but it is not the case anymore. What is
    the easiest way to print all this info while within GRC?

You can print the result of the set_center_frequency(), it returns a
tune_request struct with RF and DSP frequency fields.

-josh

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