[USRP-users] timeout in tx_timed_samples

Marcus D. Leech mleech at ripnet.com
Wed Nov 8 13:02:58 EST 2017


On 11/08/2017 09:48 AM, Hojoon Yang via USRP-users wrote:
>
> Hi all,
>
> In the example tx_timed_samples.cpp
>
> there is tx_stream->send(... , ... , ..., timeout)
>
> How the timeout works?
>
> when I set the value of timeout zero or 0.00001, I expect that the 
> terminal show the "Send timeout..."
>
> because it will not have enough time to send all samples during 
> timeout 0.(I expect that it will send 0 samples)
>
> it will timeout before entire transmission of samples..
>
> But seems that it works perfectly.. it prints out Sent packet : 2044 
> which is the maximum value of samples..
>
> How the timeout works!?!?
>
> Thanks in advance!!
>
>      size_t num_acc_samps = 0; //number of accumulated samples
>      while(num_acc_samps < total_num_samps){
>          size_t samps_to_send = std::min(total_num_samps - 
> num_acc_samps, buff.size());
>
>          //send a single packet
>          size_t num_tx_samps = tx_stream->send(
>              &buff.front(), samps_to_send, md, timeout
>          );
>
>          //do not use time spec for subsequent packets
>          md.has_time_spec = false;
>
>          if (num_tx_samps < samps_to_send) std::cerr << "Send 
> timeout..." << std::endl;
>          if(verbose) std::cout << boost::format("Sent packet: %u 
> samples") % num_tx_samps << std::endl;
>
>          num_acc_samps += num_tx_samps;
>      }
>
>      //send a mini EOB packet
>      md.end_of_burst   = true;
>      tx_stream->send("", 0, md);
>
>
The timeout is, as far as I know, applied to the underlying socket call, 
or libusb write call.   I many situations, that kernel-call won't block, 
because the
   kernel-side buffering is large enough that it will almost never need 
to block.


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