[USRP-users] Time of arrival of first sample in a 2 Rx setup

Marcus Müller marcus.mueller at ettus.com
Thu Apr 23 08:55:10 EDT 2015


Hey Siva,

I assume this means you have two B210s?
Sorry, I don't really have a picture of your setup in mind, would you
mind making a sketch?

Best regards,
Marcus

On 04/23/2015 02:53 PM, siva sankar wrote:
>
> Hey Marcus,
>
> Thanks for the reply.
> The receivers here are at different distances from the transmitter and
> we are looking for the time difference of arrival of the samples at
> the receive buffers.
>
> How do we proceed with this ?
>
> Regards
> Siva
>
> Hello Siva,
> recv() will do an aligned reception, i.e. the first samples of both
> streams were received at the same time.
>
> Often, you don't want to /know/ /afterwards/ the time of reception,
> you want to /define/ it beforehand. You can do that by using a
> stream_cmd with a stream_now = false and a timespec to allow you to
> define when the reception is going to take place.
>
> Greetings,
> Marcus
>
>
> On 04/23/2015 12:28 PM, siva sankar via USRP-users wrote:
>> Hello List,
>>
>> I am using USRP B210 and the UHD version is 003.008.000. We are
>> transmitting on one channel and receiving simultaneously on both the
>> channels and what we want is the time of arrival of the first sample
>> in both the receive buffers. 
>>
>> We have used the "time_spec_t" to get the time of the first sample
>> but we don't know if the time that we are getting is for both the
>> channels or for one of the receiver buffers.
>>
>> We have tried using two "recv" commands one for each buffer hoping we
>> could calculate the time from each metadata parameter passed to the
>> "recv" command in one thread  but it throws "multi channel alignment"
>> error and stops running.
>>
>> We also tried to create individual threads for both the rx channels
>> and pass different metadata parameters and hence know the time of
>> first sample for each buffer. However, this throws segmentation fault. 
>>
>> Any help on how to calculate the time of first sample for each
>> receive buffer will be appreciated.
>>
>> Thanks
>> Siva.
>>
>>
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>
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