gr-soapy: Add timestamp tag to source output

[NZSmartie]

Feature Description

SoapySDR will provide the hardware timestamp of the received buffer in the form of nanoseconds. gr-soapy's source block discards this timetamp time_ns when outputting items.

gnuradio/gr-soapy/lib/source_impl.cc

Lines 51 to 97 in 6c34c6b

	int source_impl::general_work(int noutput_items,
	[[maybe_unused]] gr_vector_int& ninput_items,
	[[maybe_unused]] gr_vector_const_void_star& input_items,
	gr_vector_void_star& output_items)
	{
	long long int time_ns = 0;
	int flags = 0;
	const long timeout_us = 500000; // 0.5 sec
	int nout = 0;
	for (;;) {
	// No command handlers while reading
	int result;
	{
	std::lock_guard<std::mutex> l(d_device_mutex);
	result = d_device->readStream(
	d_stream, output_items.data(), noutput_items, flags, time_ns, timeout_us);
	}
	if (result >= 0) {
	nout = result;
	break;
	}
	switch (result) {
	// Retry on overflow. Data has been lost.
	case SOAPY_SDR_OVERFLOW:
	std::cerr << "sO" << std::flush;
	continue;
	// Yield back to scheduler on timeout.
	case SOAPY_SDR_TIMEOUT:
	break;
	// Report and yield back to scheduler on other errors.
	default:
	d_logger->warn("Soapy source error: {:s}", SoapySDR::errToStr(result));
	break;
	}
	break;
	};
	return nout;
	}

Can we add a time tag to the output much like gr-uhd does (and possible the frequency and rate as well?)

gnuradio/gr-uhd/lib/usrp_source_impl.cc

Lines 623 to 630 in 1dcf874

	this->add_item_tag(i, nitems_written(0), TIME_KEY, val, _id);
	this->add_item_tag(
	i, nitems_written(0), RATE_KEY, pmt::from_double(_samp_rate), _id);
	this->add_item_tag(i,
	nitems_written(0),
	FREQ_KEY,
	pmt::from_double(this->get_center_freq(i)),
	_id);

Feature Urgency

medium (would be nice to have in the near future)

More Information

No response

[willcode]

Since hardware timestamps are not provided by all hardware, there would need to be a switch for this.

[NZSmartie]

AFAIK there's no easy way to detect if a Soapy driver's Stream API supports timestamps, it just gets filled out if supported. untouched otherwise.
the drivers that support timestamps are:

• HackRF - https://github.com/pothosware/SoapyHackRF/blob/79077f0425f732954c1d74dbbacd788b0ac7d733/HackRF_Streaming.cpp#L623
• BladeRF - https://github.com/pothosware/SoapyBladeRF/blob/85f6dc554ed4c618304d99395b19c4e1523675b0/bladeRF_Streaming.cpp#L385
• RTLSDR - https://github.com/pothosware/SoapyRTLSDR/blob/40d0708b009cac1a77f9a7c4052b2f3951b08f60/Streaming.cpp#L509
• LimeSDR - https://github.com/myriadrf/LimeSuite/blob/f81c496176ca7e861d0b0f9a8dcb4cea62b1176d/SoapyLMS7/Streaming.cpp#L447

These Soapy drivers don't populate the timestanp:

• PlutoSDR - https://github.com/pothosware/SoapyPlutoSDR/blob/a07c37230369653818b3a5c448c00cee1ac9f8e5/PlutoSDR_Streaming.cpp#L239
• AirSpyHF - https://github.com/pothosware/SoapyAirspyHF/blob/d6825331a6bfc3578dc6fe5091fce3d550b6af3c/Streaming.cpp#L282

Since each driver supported is defined as a seperate source and sink block in gr-soapy. it might be worth while adding a argument to the other_settings parameter.

Alternatively, since each driver that doesn't support hardware timestamps, does not alter its value. Setting it to -1 prior to calling readStream() and checking for any positive value be a requirement for adding the tag.