Hi Eric,
this mail kind of fell through the cracks. Have you found a solution to
this, yet?
It's not overly clear from the documentation, but the finite_acquisition
method really bypasses parts of what you configure as behaviour for the
USRP_source. So, ok, that won't work.
The second one might be slightly off, syntaxwise. You'll need to create
a stream_cmd_t (of the right type), not use one of the type constant
fields of stream_cmd_t (just as you do in the next approach).
The third might work, but really breaks GNU Radio idea of processing
streams of samples; so, I'm not 100% sure what is appropriate for you :(
Best regards,
Marcus
On 04/24/2017 09:30 PM, Eric Martin wrote:
> I'm using the GNURadio python interface to UHD, and I'm trying to set
> a specific time to start collecting samples and either collect a
> specific number of samples or stop the collection of samples at a
> specific time. Essentially, creating a timed snapshot of samples. This
> is something similar to the C++ Ettus UHD example 'rx_timed_sample'.
>
> I can get a flowgraph to start at a specific time, but I can't seem to
> get it to stop at a specific time (at least without causing
> overflows). I've also tried doing a finite aquisition, which works,
> but I can't get it to start at a specific time. So I'm kind of lost at
> what to do next.
>
> Here is my try at the finite acquisition (seems to just ignore the
> start time and collects 0 samples):
>
> num_samples = 1000
>
> usrp = uhd.usrp_source(
> ",".join(("", "")),
> uhd.stream_args(
> cpu_format="fc32",
> channels=range(1),
> ),
> )
>
> ...
>
> usrp.set_start_time(absolute_start_time)
> samples = usrp.finite_acquisition(num_samples)
>
>
> I've also tried some combinations of following without success
> (TypeError: in method 'usrp_source_sptr_issue_stream_cmd', argument 2
> of type '::uhd::stream_cmd_t const &'):
>
> usrp.set_command_time(absolute_start_time)
> usrp.issue_stream_cmd(uhd.stream_cmd.STREAM_MODE_NUM_SAMPS_AND_DONE)
> I also tried the following in a flowgraph:
>
> ...
> usrp = flowgrah.uhd_usrp_source_0
> absolute_start_time = uhd.uhd_swig.time_spec_t(start_time)
> usrp.set_start_time(absolute_start_time)
>
> flowgrah.start()
>
> stop_cmd = uhd.stream_cmd(uhd.stream_cmd.STREAM_MODE_STOP_CONTINUOUS)
> absolute_stop_time = absolute_start_time +
> uhd.uhd_swig.time_spec_t(collection_time)
>
> usrp.set_command_time(absolute_stop_time)
> usrp.issue_stream_cmd(stop_cmd)
>
> For whatever reason the flowgraph one generated overflows consistently
> for anything greater than a .02s collection time.
>
> I posted this question on stack overflow without any success:
> http://stackoverflow.com/questions/43420300/how-to-receive-a-finite-number-of-samples-at-a-future-time-using-uhd-gnuradio
>
> Any help would be greatly appreciated!!
>
> Thanks.
>
>
>
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