On 06/21/2021 07:33 PM, Alex Bouvy via USRP-users wrote:
Hi Marcus,
Got it, makes sense! Thanks for the info.
Regards,
Alex
We should perhaps for a moment consider what it would mean for the
hardware to adorn every single sample with a time-stamp.
Over-the-wire samples occupy 4 bytes (16-bit I 16-bit Q). Timestamps
are (AFAIR) 64 bits or 8 bytes. If every single sample
were adorned with a time-stamp *on the wire*, that would *triple* the
occupied bandwidth of samples flowing over the wire--meaning
less bandwidth would be available for actual samples.
Similarly, if UHD adorned every sample as it arrived, there'd be
considerable ballooning of memory occupancy, and memory-bandwidth
consumption. Putting in all this overhead to avoid a simple
calculation on the part of the application writer would be bad
engineering, IMHO.
-----Original Message-----
From: Marcus Müller <[email protected]>
Sent: Monday, June 21, 2021 5:31 PM
To: [email protected]
Subject: [USRP-users] Re: Adding Timestamps to B210 RX Samples
Hi Alex,
that's the right (and only) approach: Metadata contains the time stamp for the
first sample in a packet; the rest is counting!
Best regards,
Marcus
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On 22.06.21 00:24, Alex Bouvy via USRP-users wrote:
Hello,
In the paper below, the authors say that they have set up their USRP
device to include timestamps for each recorded sample, but do not provide
detail on how this was achieved:
https://ieeexplore.ieee.org/document/6533293
<https://ieeexplore.ieee.org/document/6533293>
I have been looking into what is required to achieve something
similar. Particularly, I have been working with the source code of the
rx_timed_samples.cpp example provided in the UHD files, along with this page in
the Ettus manual:
https://files.ettus.com/manual/page_sync.html
<https://files.ettus.com/manual/page_sync.html>
Looking through the rx_timed_samples code, it appears that the
metadata associated with the recv(..) function contains a time_spec
field which is the timestamp for the first sample in the IO stream,
but it's not immediately clear to me how that might be used to
timestamp all of the samples, which makes me think this may be the wrong
approach. Is there a simpler method to do this that is known?
Tangentially, I've also looked into adding the timestamps through
GNURadio, but there does not appear to be a way to do this as far as I can tell.
Any help is much appreciated.
Thank you,
Alex
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