[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] using general_work when output rate is not fixed

From: Rahman, Muhammad Mahboob Ur
Subject: Re: [Discuss-gnuradio] using general_work when output rate is not fixed
Date: Tue, 25 Sep 2012 16:02:09 +0000

Hi Tom & All,

I am now doing consume_each(noutput_items) but my problem is not solved yet. I 
have also made sure that my code effectively sends one sob tag and one eob tag 
per burst of samples.

Questions about new experiment:
Now, I have created yet another simple experiment whose flow-graph is as 

uhd usrp source --> my custom block --> uhd usrp sink
                                                       --> file sink

The relevant code of my custom block is below:
howto_send_discont::general_work (...) {

  int ninput_items_used_in_this_work_call;
  ninput_items_used_in_this_work_call = 0;

  for (int i = 0; i < noutput_items; i++){

    if (samp_count == 1) { out[i] = gr_complex(0.7,0); 
    else if (samp_count == 2) { out[i] = gr_complex(0.7,0); 
    else if (samp_count == 25000) {
    samp_count = 0; send_tx_pkt = true; pkt_no++; }
    if (send_tx_pkt) {
        /*if (total_samps_outputted_so_far == 7761) {
               pkt_samp_no = 1; samp_count = 1; total_samps_outputted_so_far = 
10000; pkt_no = 0; }
        else if (total_samps_outputted_so_far < 7761){  
               total_samps_outputted_so_far++; }*/
        out[i] = gmsk_pkt_samples_2[pkt_samp_no-1];
        if (pkt_samp_no == 1) {
        else if (pkt_samp_no == 1536) {
            pkt_samp_no = 0;
            send_tx_pkt = false;

  consume_each (noutput_items);

  // Tell runtime system how many output items we produced.
  return ninput_items_used_in_this_work_call;

You can see from the above code that my custom block maintains an internal 
counter samp_count which causes the custom block to output N samples whenever 
internal counter's count equals M (N=1536, M=25000 in my case). I use the same 
counter to initially send a burst of 2 samples to uhd usrp sink after attaching 
sob and eob tags so as to avoid underflow problem at the transmit side. But my 
problems are persistent which are:

- I see many zero-valued samples among the first 7761 output samples of my 
custom block, even when the samples my custom block should output are either 
constant valued samples or pre-recorded GMSK samples (depending upon which line 
is uncommented in my above code). Why it is so? 

- Even though I have avoided the above mentioned problem by noticing that in my 
case, after first 7761 samples, all the subsequent samples are correct. So, I 
use another counter to start all over again (to reset the functionality of my 
block) once my custom block has sent 7761 samples to uhd usrp sink. Now, the 
other issue is, when I send pre-recorded GMSK samples to the uhd usrp sink, I 
still see lot of underruns occuring indefinitely at tx side. Why are the sob 
and eob tags being ineffective? Moreover, when those GMSK packets are received 
at another node, the packet decode rate is too low over there (I guess not all 
of the samples corresponding to many GMSK packets are being transmitted from 
node1, fix me). 

Thanks in anticipation for your help,

reply via email to

[Prev in Thread] Current Thread [Next in Thread]