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.

chris

From: Jonathon Pendlum [mailto:jonathon.pend...@ettus.com]
Sent: Tuesday, June 27, 2017 12:18 PM
To: Hood, Christopher L. <christopher.h...@gtri.gatech.edu>
Cc: usrp-users@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?

Jonathon

On Thu, Jun 22, 2017 at 2:12 PM, Hood, Christopher L. via USRP-users 
<usrp-users@lists.ettus.com<mailto:usrp-users@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.

Thanks,
chris



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