Hi
We have a Setup with single x310 and 2 twinrx
We use Ubuntu 16.04
linux; GNU C++ version 5.4.0 20160609; Boost_105800; UHD_3.11.0.1-0-ga1b5c4ae
We have an Rx application
We sync all channels(ch0-3) to ch0 lo.
We use internal clock 1pps
We are trying to sample 4 channels,
each time for  a defined period of time,
Each time on a different frequency.
We have issues syncing the channels and get strange results calculating phase 
difference

Case 1:
We zero the time on each sample (not what we would ilke to do)
We than get the same phase difference  for a fixed frequency entered using a 
signal genrator

                                                                
gDevice->usrp()->set_time_unknown_pps(uhd::time_spec_t(0.0));
                                                                
uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_NUM_SAMPS_AND_DONE);
                                                                
stream_cmd.num_samps   = streamLength;
                                                                
stream_cmd.stream_now  = false;
                                                                
stream_cmd.time_spec   =  uhd::time_spec_t(0.2);
                                                                
rx_stream->issue_stream_cmd(stream_cmd);
case 2:
                                                                
uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_NUM_SAMPS_AND_DONE);
                                                                
stream_cmd.num_samps   = streamLength;
                                                                
stream_cmd.stream_now  = false;
                                                                
stream_cmd.time_spec   =  gDevice->usrp()->get_time_now() + 
uhd::time_spec_t(0.2);
                                                                
rx_stream->issue_stream_cmd(stream_cmd);

on case 2 we get different phase phase difference  on each recording,
the phase difference is changing each time in +-(90/180/270)

can you explain ?
why does gDevice->usrp()->set_time_unknown_pps(uhd::time_spec_t(0.0))
need to get a fixed offset?

Why if we don't do it we get +-(90/180/270) degrees ?
This happens also if we wait for the next pps.


What we would like to d0
As soon as we get a command - try and sample a define times for all channels
This is done in a loop
Can this be done differently?  We tried continuous start stop with no success 
and also

Thanks
Ilay
Software Team Leader


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