At the very benign 20 MS/s, I'd really say your first option is the way
to go. The rest probably won't work very well du to turn on/off
behaviour requiring you to zero pad a bit to flush your TX data chains.
You can of course also write an RFNoC block to store and generate data
in-FPGA, but really: at 20MS/s just continously stream. Even a bog-
normal Gigabit Ethernet card has plenty enough bandwidth to do that. I
doubt sending a sequence from RAM will occupy much CPU on your host PC.
Best regards,
Marcus
On Thu, 2019-07-18 at 22:58 +0200, Cédric Hannotier via USRP-users
wrote:
> Dear all,
>
> I would like to periodically send a frame with an USRP X310 (frame
> length: 320 samples, rate: 20 MS/s, period: 1-500 ms). However, I
> struggle to find the best way to implement it. What I have tried so
> far:
>
> 1. Append zeros to the frame to reach the expected period.
> However,
> this consumes too much bandwidth due to the zeros.
>
> 2. Use tx_streamer->send() with a tx_metadata_t.time_spec and
> tx_streamer->recv_async_msg(). Using that, only the frame is sent,
> saving most of the bandwidth. However, with small periods, it tends
> to
> print some 'L'.
>
> 3. Buffer a batch of send request on the USRP, then wait a
> specific
> time (using eg. recv_async_msg() until the returned metadata
> contains
> the penultimate time_spec (I expect that the time_spec returned is
> the
> one specified in the send metadata)) and redo. The issue is that I
> was
> not able to find the buffer size (is it related to the
> tx_streamer->get_max_num_samps()?). I would like to fill the buffer
> without overflow.
>
> I was hoping that I could save the frame in an USRP's memory, and
> then
> ask it to periodically send the frame with a specific period. Is it
> possible?
>
> Here is an example of (2):
>
> template <typename samp_type>
> void send_from_file(const uhd::usrp::multi_usrp::sptr &usrp,
> uhd::tx_streamer::sptr tx_stream, const
> std::string&
> file,
> const double period)
> {
> size_t data_size = get_file_size<samp_type>(file);
> std::ifstream infile(file, std::ifstream::binary);
> std::vector<samp_type> buff(data_size);
> infile.read(reinterpret_cast<char*>(buff.data()),
> (std::streamsize)(buff.size()*sizeof(samp_type)));
> infile.close();
> size_t num_tx_samps = buff.size();
> std::cout << file << " " << buff[0] << " " << num_tx_samps <<
> std::endl;
>
> uhd::tx_metadata_t md;
> md.start_of_burst = true;
> md.end_of_burst = true;
> md.has_time_spec = true;
> md.time_spec = usrp->get_time_last_pps()+5.;
> double timeout = md.time_spec.get_real_secs();
> uhd::async_metadata_t md_status;
>
> while (not stop_signal_called) {
> tx_stream->send(&buff.front(), num_tx_samps, md);
> if (tx_stream->recv_async_msg(md_status, timeout)) {
> if (md_status.event_code !=
> uhd::async_metadata_t::event_code_t::EVENT_CODE_BURST_ACK) {
> std::cerr << "Error: " << md_status.event_code
> << std::endl;
> exit(EXIT_FAILURE);
> }
> } else {
> std::cerr << "timeout before sent" << std::endl;
> exit(EXIT_FAILURE);
> }
>
> timeout = 0.1;
> md.time_spec += period;
> }
> }
>
>
>
> Best Regards,
> Cédric
>
> _______________________________________________
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> USRP-users@lists.ettus.com
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