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

[Harry Zhang]

Dear Miklos,
    Yes, I do never stop receive program. I'm using USRP N210, WBX, 
Ubuntu12.04 and UHD3.5.3. I'm writing a document in detail, which will 
be sent to you later today.

Best,
Harry

 2013/11/3 22:47, Miklos Maroti wrote:
> Hi Harry,
>
> You never stop the receiver on node B and C, right? You should not
> observe anything like that if you do not have dropped packets. Are you
> using USRP2's?
>
> Miklos
>
> On Sat, Nov 2, 2013 at 3:05 AM, Harry Zhang <address@hidden> wrote:
> > Tom,
> >      Thanks for your reply.
> >      I got a weird problem when using rx_time tags. I have three nodes, node
> > A sends 10 packets within 0.2 sec ,stops for 1sec sends 10 packets ,
> > stops..., sends....,stops....  . Node B and C receive it and record the
> > receive time using (rx_time+ sample_count*sample_rate).  Considerating the
> > clock offset between B and C, the difference of B and C's receive time must
> > remain stable. But every time after A stops for 1sec, the receive time's
> > difference varies several hundreds of microsecond. I'm stumped by this
> > problem.
> >      Could you give me some advice. Thank you in advance.
> >
> > Harry
> >
> > 2013/11/1 22:26, Tom Rondeau wrote:
> > > 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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