I created an hier block that does exactly that: run it once, reload your
blocks, and then use the "QT GUI Record Button" block as a sink in other
flowgraphs.

Thank you Derek for sharing Nate's flowgraph - my block had been using a
selector block, and created a 0-byte file every time a flowgraph using it
was run. Using "if/then" in the file sink like Nate did eliminates that!

Best,
Michael Morrison

On Tue, Aug 16, 2016 at 12:47 PM, Derek Kozel <[email protected]> wrote:

> Hello Mike,
>
> Here is a simple, but clever, flowgraph put together by Nate Temple which
> does exactly what you describe. It isn't an answer to the time errors
> you've seen, but I hope it is useful anyways.
>
> Regards,
> Derek
>
> On Tue, Aug 16, 2016 at 9:08 AM, Marcus Müller <[email protected]>
> wrote:
>
>> Hi Michael,
>>
>> what USRP are you using, and which version of UHD?
>>
>>
>> Best regards,
>>
>> Marcus
>>
>> On 16.08.2016 17:41, Michael Giallorenzo wrote:
>>
>> Hi everyone,
>>
>> I'm currently trying to develop a gui for recording selected samples of
>> data while viewing the spectrum (the user can watch a waterfall display of
>> the readings being taken on an Ettus x310, and press and hold a button to
>> record data when the spectrum looks interesting).
>>
>> The combination of the burst tagger block and the tagged file sink block
>> in GRC seem to be the perfect solution to this, but I'm noticing an error
>> whenever i change the frequency during execution. The timestamps recorded
>> in the resulting filenames rapidly jump ahead in time (easily confirmed by
>> comparing the filenames to the output of the tag debug block or writing the
>> same data to a metadata file and reading its header). When I'm using my
>> GPSDO as a time source, the time starts out in sync with GPS but rapidly
>> gets corrupted as i change the frequency. Likewise when I use relative
>> time, timestamps start at 0 but increase too quickly.
>>
>> As far as I can tell, this is because the tagged file sink block is not
>> seeing the rx_time tags on the data stream and is instead trying to
>> calculate the time based on the sample rate, but is confused when the
>> changing frequency results in extra tags that are effectively being
>> generated faster than expected.
>>
>> I'm fairly new to gnuradio and my background isn't really software but
>> I've been experimenting with OOT modules and have modified a few built in
>> blocks to suit my needs before. In "tagged_file_sink_impl.cc" around line
>> 100, i believe time_tags_outer.size() is returning a value of 0 and that
>> may be the source of my problems. Perhaps this stems from my lack of
>> understanding of how the scheduler calls the work function (ie how is the
>> value of noutput_items determined?), but I'm not really sure how to modify
>> this or really why this is happening.
>>
>> Sorry if my thoughts here are kind of all over the place. Any insight or
>> reading material that anyone could offer would be greatly appreciated.
>>
>> Thanks,
>>
>> Mike G
>>
>>
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