USRP Software Radio

[mki]

Hello,

I am now attempting to recieve signals from 4 boards synchronously. Using the attached VI, if I set two boards to operate from an external reference and two others to use MIMO, I receive an error at the Initiate vi that ~The reference clock PLL did not lock within the alloted time. However, if I only use MIMO on one board and operate the other three boards off an external reference the VI works fine. Am I missing something?

[ErikL]

The basic harware theory of operation is:
1. The MIMO cable allows one USRP to act as master and the other as slave. (You will need to set the second USRP to use the MIMO cable for two properties: 10 MHz Reference Frequency Source and Timebase Clock Source.)
2. The 10MHz referece clock is then shared direclty over the cable, while timestamps are shared over the cable to sync time between devices.
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The basic software theory of operation:
1. Use the Configure Trigger VI to specify at what time you want to acqusition to start
2. Synchronize the times across USRP using the Set Time (specify that this should happen on "Next Timebase Edge")
3. Commit the changes
4. Run a Fetch or Write... it will wait until the time base reaches the 'Trigger' time to start
 
Refer the following shipping example for help:
niUSRP EX Rx Multiple Synchronized Inputs.vi
 
(Note: If you're not using the MIMO cable, but rather the external Ref In and PPS inputs then you need to remove the "0" wired in to the top channel list input of the niUSRP Set Time.vi)
 
Best Regards,
Erik
 

[mki]

Hi Erik,

I realized I forgot to save the values I was using as defaults, so it probably was not very clear how I set up the boards.

ch0 was connected to ch1 with a MIMO cable, ch3 was connected to ch2 with another MIMO cable.

External references for RefIn and PpsIn was connected to ch1 and ch2.

When I run the VI, I get the error I mentioned before about the pll not locking. However, I am certain that there are no problems with the external reference as the VI works fine if I connect all four boards to the external reference without using the MIMO cable. Also, the VI can synchronously receive from two boards without any errors using a MIMO cable. As such, I was wondering whether there was anything I need to be aware of in the case when there are more than one master each with its own slave.

[ErikL]

You configuration sounds fine. I have setup the same config before. The master devices should be configured for external ports and the MIMO for getting their signals from the MIMO cable.

The important thing to note is that you only need to reset time to 0 on channels with external triggered devices. Set the 1,2 in the pink string input on the top of the set time VI. Also use next rising edge.