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

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 <zhangnow@gmail.com> 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 <zhangnow@gmail.com> 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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