Synchronised transmission on each channel of 2 USRPs (2952R)

[SteCla]

Hi!

I want to generate a signal on 4 antennas using 2 usrp 2952Rs.

One should output its reference frequency and pps to the other one using tha connectors on the backend.

I started from the example "niUSRP EX Rx Multiple Synchronized Inputs (PPS Trig)" which is limited to two channels. When I try to expand it to 4 I get the error:

Error -1074118627 occurred at niUSRP Export Signal.vi

Possible reason(s):
A runtime or configuration error occurred.
Code: 312
Details: EnvironmentError: IOError: Radio ctrl (A) no response packet - AssertionError: bool(buff)
  in unsigned __int64 __thiscall radio_ctrl_core_3000_impl::wait_for_ack(const bool)
  at ..\..\lib\usrp\cores\radio_ctrl_core_3000.cpp:198

To be specific, when I modify "Enabled channels" to 0,1 or 0,2 or 1,2 or ... it works, when I put 0,1,2 or 0,2,3 or... it fails. The 'master' exports the 2 signals (ref.Freq and pps) using "niUSRP Export Signal.vi" and that is where the error occurs. Btw, the error occured for the first time where the IQ Rate is read, I removed that property which didn't help.

Then I started thinking about channels and I read:

http://forums.ni.com/t5/USRP-Software-Radio/Sessions-Devices-and-Channels/m-p/2874970/highlight/true...

I read:

http://forums.ni.com/t5/USRP-Software-Radio/how-to-synchronize-multiple-usrp-rio-294x-devices/td-p/3...

But he uses a Octoclock and how I modified the example to a 4-channel version is not clear.

This community-example gave me hope:

https://decibel.ni.com/content/docs/DOC-43878

But it only supports 2 channels.

What I basically need is access to the 4 transmitters, controlling their gain and send a specific signal with each of them. Hence, a transmitter of a 4x1MISO built with two USRP 2952R's.

One of the articles I mentioned says:

4) Similar rules apply to reading attribute values back, but you can get into trouble.  If you read an attribute with a wide scope (e.g. read Gain with a "" Active Channel) it will return a valid value ONLY if all of the channels in the session have the same value for that property.  Otherwise, you get an error.

I am expecting that this may cause problems... However the channel combination '0,1' AND '0,2' work... .

Any ideas?

[SteCla]

correction: only Enabled channels = (0,1) OR Enabled channels = (2,3) works.