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

siva sankar sankar.siva730 at gmail.com
Thu Apr 23 08:53:54 EDT 2015

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 ?

  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.


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.


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