Re: [Discuss-gnuradio] Issues with syncing two USRPs!

[Martin Braun]

On 10.06.2014 22:09, khalid.el-darymli wrote:
> I am a new user of USRP/GNU Radio. I am  experimenting with a system
> comprised of one transmitter and multiple receivers. For now, I have two
> USRP N200. On the first USRP, I got one LFTX and one LFRX daughter
> boards. On the other, I got one LFRX daughter board.
>
> In my application, it is important that the transmit and receive
> channels are synchronized (i.e., both device  time and channel phase).
> For this, I am using my own GPS and PPS signals.

What's the source of these signals? Have you made sure they are 
generating the right thing (i.e. 10 MHz ref)?

Out of curiousity, do you have a MIMO cable and are willing to test that?

> For the sake of testing, I am feeding the output of LFTX to all the
> inputs in LFRX (i.e., four receive channels). The output/input type is
> Complexfloat32. In GRC, when I use a separate USRP source block  for
> each motherboard (i.e., without synchronization), the system is working
> and I can receive four unsynchronised replicas of my transmitted signal.

You're saying you get 2 channels per LFRX, correct? Also, are you 
attenuating the signal?

> However, when I a use a single USRP source with two-motherboard and
> four-channel options, I get the following error message:
>
>
> linux; GNU C++ version 4.8.2; Boost_105400; UHD_003.007.001-68-gc4b1f810
>
> -- Opening a USRP2/N-Series device...
> -- Current recv frame size: 1472 bytes
> -- Current send frame size: 1472 bytes
> -- Opening a USRP2/N-Series device...
> -- Current recv frame size: 1472 bytes
> -- Current send frame size: 1472 bytes
> --     1) catch time transition at pps edge
> --     2) set times next pps (synchronously)
> Using Volk machine: sse4_a_64_orc
> *thread[thread-per-block[4]: <block gr uhd usrp source (1)>]:
> RuntimeError: fifo ctrl timed out looking for acks*
>  >>> Done
>
> My sample rate is 100e6/128 Hz. In the USRP source I set  synch to:
> UnknownPPS, Mb0/1 clock source and Mb0/1 time source to EXTERNAL.  Mb0/1
> subdev spec: A:A A:B. I tried to change the WireFormat from AUTOMATIC to
> ComplexInt16 without any difference.

Just to confirm: You're setting *both* clock and time sources to external?

M

> I checked ./test_pps_input and I got a 'success'. I think the issue has
> to do with the settings for syncing.  Any ideas on what causes this problem?
>
> BTW, I am also aware of this link
> (http://files.ettus.com/uhd_docs/manual/html/sync.html), but I am not
> sure where the commands of synchronizing the device time and channel
> phase  should be applied?
>
>
> Thank you.
>
> Best regards,
> Khalid
>
>
>
>
>
>
>
> On Tue, Jun 10, 2014 at 1:31 PM, <address@hidden
> <mailto:address@hidden>> wrote:
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