04-20-2012 10:26 AM
I have a VI that, start transmiting samples at a specified trigger time , this worked fine with 1.0 drivers , now with 1.1 driver i get :
"niUSRP Write Tx Data (CDB WDT).vi<ERR>Packet had timestamp that was late (or too early)."
is it somthing i have to change in the setup of the USRP to use the new driver?
(i have uppdated the FW & FPGA)
04-20-2012 03:09 PM
Hi Ole robert,
Unfortunately I no longer have 1.0 installed on my machine, but to get the trigger working incorrectly with 1.1, you need to set the time as well as configure the trigger. Since the trigger is configured based off a given start time, it is important to zero out the time value of the onboard device timer. If you don't do this, there is a possibility that it will not start at zero and the value that you specify for the start trigger time may have already passed. Here is a screen shot of how to set this up:
As I mentioned, I don't currently have a system to check how the trigger was set up before, but using these 2 VIs you should take care of the error. If you are still having issues let me know and I'd be happy to help.
04-24-2012 07:45 AM
I do it slightly different , i set the trigger time first then later in the diagram just before start transmit i set the clock to 0 time.
I have discovered that i have to send less than 1.2 MSamples of data in one call to "niUSRPwrite TX data.vi" to avoid geting buffer underrun
now i manage to run the application at 3.125 MSPS(with flow control on the ethernet adapter disabed) , before(with the 1.0 driver) i run at 12.5MSPS
without doing anything with the ethernet adapter. so somthing have changed?
04-24-2012 05:07 PM
Hi Ole Robert,
As to what changes were made, I cannot give a good answer. However, I do have a work around.
If you look in the NI-USRP Help document, there is section called Data Streaming Performance Tips. To get back to the rates that you saw with the 1.0 driver (and better based on benchmarking tests I have run), you will have to make a change to one of your registry keys, FastSendDatagramThreshold. You will need to change this value to greater than 1500. I set mine to 2048 and had good results. The help document has more details about how to change this registry key.