[USRP-users] X310 transmit underflow when sampling rate is low

Hood, Christopher L. Christopher.Hood at gtri.gatech.edu
Fri Jul 7 15:49:09 EDT 2017

Sorry for the late reply,

The MTU is set to 9000.

The time spec was varied from a few dozen ms up to several seconds in the future with
no change in behavior.


From: Jonathon Pendlum [mailto:jonathon.pendlum at ettus.com]
Sent: Tuesday, June 27, 2017 12:18 PM
To: Hood, Christopher L. <Christopher.Hood at gtri.gatech.edu>
Cc: usrp-users at lists.ettus.com
Subject: Re: [USRP-users] X310 transmit underflow when sampling rate is low

Hi Chris,

What is your MTU size set to? How far into the future do you set the timespec?


On Thu, Jun 22, 2017 at 2:12 PM, Hood, Christopher L. via USRP-users <usrp-users at lists.ettus.com<mailto:usrp-users at lists.ettus.com>> wrote:
I’m running a simple one pulse loopback transmit/receive and am running into transmit underflows when the sampling rate is LOW. Specifically, for my short 30 us pulse, the underflow occurs when the sampling rate is 5 MHz or lower. I ran the test at 10, 20, 25, 33.3, 50, 100, and 200 MHz with no issues at all. The X310 is connected to the host over 10 gig Ethernet, and the tx stream send command is set with metadata so start of burst=1, end of burst=1, has time=1, and with the time spec well into the future wrt the device. The send command returns without incident, and when the time spec elapses, the async message is received, which indicates an underflow. Looking at the receive samples, the underflow appears to occur at the beginning of the intended transmission, because much of the intended waveform is being received.

Any direction into fixing this issue would be appreciated.


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