[Discuss-gnuradio] Using "send_now=0" on USRP2

[Per Zetterberg]

Dear All,

I am trying to issue 50000 calls to tx_16sc (of 371 samples each i.e.,
one ETH packet per call) to the USRP2. I transmit a simple sinuswave. If
I set "send_now=1" in the metadata it works as expected and I can see
the signal on a spectrum analyzer. If I set send_now=0 I can only
occasionally see the signal pass and then for only very short time. Here
are some more details: I first receive a few frames to get the
time-stamp from the received frames, this timestamp is stored in the
variable last_time_stamp. Then I transmit using the code below (the
interpolation factor is set to 10). Is there anything I have
misunderstood ? 

metadata.send_now=0;
metadata.start_of_burst=1;
metadata.end_of_burst=1;

int i1;   
for (i1=0;i1<NO_ITER-1;i1++) {

    metadata.timestamp=last_time_stamp+10e6+i1*NO_SAMPLES*10;
      
    if (!u2->tx_16sc(0,
        buffer,
        NO_SAMPLES,
        &metadata)) {
         printf("Transmit data failed!\n");
            };
           metadata.start_of_burst=1;
     };

    metadata.end_of_burst=1;
    u2->tx_16sc(0,
                 buffer,
                 NO_SAMPLES,
                &metadata);

};


BR/
Per