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Re: [Discuss-gnuradio] How to get multipe rx_time tags while receiving c


From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] How to get multipe rx_time tags while receiving continuously
Date: Fri, 1 Nov 2013 10:26:16 -0400

On Thu, Oct 31, 2013 at 3:46 AM, Harry Zhang <address@hidden> wrote:
> Hi,
> As far as I know rx_time tag is associated with the first sample of a
> receive stream. If I wanna get multiple rx_time tags while receiving
> continuous data, should I stop and issue a new stream again and again
> for getting more rx_time tags.
> Thank you.

Harry,

We want to minimize tags through the flowgraph since it adds overhead.
The UHD driver only sends an rx_time tag whenever one is necessary.
That means that if there is a chance that the host has become
unsynchronized, it sends an updated tag. So there's one at the
beginning of the stream to set the initial time. Then, if a dropped
packet or overflow are detected, it sends a new rx_time tag.

Between time tags, you can count samples and you know the sample rate,
so you know the time of every sample based on that initial rx_time tag
(to within the tolerance of the sample clock on the USRP).

Tom



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