USRP Software Radio

cancel
Showing results for 
Search instead for 
Did you mean: 

Muliple USRP RIO 2943R, synchronization and phase lock problem

Solved!
Go to solution

BTW, for the internal signal of OctClock, i think I need GPS antenna and GPS signal to drive the GPSDO inside. As most of my experiments will take place in building, it will be tricky. 

 I will use on spare USRP to output 10M ref and PPS for others. 

 

Cheers, Bo

0 Kudos
Message 21 of 25
(1,990 Views)

@True_Boombo wrote:

BTW, for the internal signal of OctClock, i think I need GPS antenna and GPS signal to drive the GPSDO inside. As most of my experiments will take place in building, it will be tricky. 

 I will use on spare USRP to output 10M ref and PPS for others. 

 


  • You do not need a GPS antenna. The OctoClock (or, at least the OctoClock-G) will generate a 10 MHz clock and a PPS. You do not need GPS for this. Having a GPS antenna will discipline the OctoClock, but will not change the fact that the OctoClock will generate a 10 MHz clock and PPS.
  • Yes, you can use a spare USRP to output its 10 MHz reference clock and its PPS to drive the OctoClock.

 

0 Kudos
Message 22 of 25
(1,986 Views)

Hi Brooks,

I made some more test during the weekend. The results are not optimistic. Here is some quick summary.

 

First of all, I test the time based example project:

1. Start with 1 Tx USRP, 1Rx USRP, each USRP has two channels. Result: phased and time synced when sampling rate is under 40 MS/s, 40~60 is a grey area, phase locked, but the trigger time will change with seconds interval, the trigger time will become totally unstable with sampling rate over 60MMs/s

 

2. You mentioned that it may be the problem of the PXI bus. I guess may be it is potential risk part. Though, I have two CPS 8910, but I think the speed of the PXIe slot also matters. I am using PXIe 1082, had 2GB (16G bits) per slot. I feel like it should be enough to support 1Tx and 1Rx situation, but actually not. Anyway, in order to test it, I made some modification in "Rx Code.vi" in the FPGA VI to drop some data in FPGA, to reduce the pressure on PXI FIFO. I have totally make the new FPGA VI running, I created a new topic in this forum about the drop data. Ir always report me "Error -50400 occurred at Invoke Method: FIFO.Read" when I run the host VI, There must be something wrong on the FIFO write logic  

    

Cheers,

 

Bo

 

0 Kudos
Message 23 of 25
(1,965 Views)
Solution
Accepted by True_Boombo

Hi Brooks,

 

Just a quick update about the problem we discussed last week. 

 

Inspired by the point you mentioned that PXIe bus may be the bottle neck. I made some simple modification of the FPGA VI (Not the sample dropping idea metioned in the other forum discussion). Actually, I am not sure whether the PXIe bus is a bottleneck or not, but I suspect that there must timing problem on the FPGA FIFO -> PXI Bux -> Host FIFO chain. So, I change the Rx FIFO depth and TX FIFO depth from 1024 (default value) to 8192 (current setting) in FPGA.

 

Now, the 4 Tx channels and 4 Rx Channels, the system works will in 120MS/s with good phase locking and time alignment. I ganna testing the 8X8 configuration later.

 

Thanks a lot for the discussion. It is really inspiring. 

 

Cheers,

 

Bo

0 Kudos
Message 24 of 25
(1,954 Views)
Solution
Accepted by True_Boombo

Glad to hear your applicaiton is working! One more point:

 

@True_Boombo wrote:

 

 

I made some simple modification of the FPGA VI (Not the sample dropping idea metioned in the other forum discussion). So, I change the Rx FIFO depth and TX FIFO depth from 1024 (default value) to 8192 (current setting) in FPGA.


Increasing the FPGA FIFO sizes can help mitigate overflows/underflows, yes. One thing to note is that if you set the 'number of samples' on the host to a value larger than the FPGA FIFOs, you'll always run the risk of overflow/underflow. If 8192 samples is sufficient, then you're all good. You can also use the default FPGA FIFO sizes and reduce the 'number of samples' on the host to ~1000.

Message 25 of 25
(1,952 Views)