[USRP-users] Underflows problem but limited CPU usage

Damien Serant damien.serant at gmail.com
Tue Dec 9 17:59:51 EST 2014

Hi list,

I'm trying to push the USRPN200 to the limit in throughput and I
experienced a quite strange underflow behavior.
Here is my configuration :

   - 2USRPN200 with Mimo cable, 25MHz and 8 bit on each with 2 Ethernet to
   avoid saturation of the link
   - Intel Xeon processor with 6 core (12 Threads)
   - Windows 7 Pro 64 bit

My UHD program is only reading samples without any processing (not even
disk writing). If i do nothing else on the PC, the program work without any
packet loss with a very limited CPU charge of about 5% (about 20% on two
cores) according to the task manager and for at least 30 minutes (the
longest test that i made). As soon as i start soliciting a bit the CPU
(e.g. opening another application, or simply by moving the scroll bar of
the console up and down or shaking the console window) underflows and
packet losses arise. I tried to play with the process priority but the
result is the same.

The underflows are apparently due to an increased CPU charge but with only
5% of CPU usage for my UHD program i should not expect that, no ?
Does anyone already experienced that ?
Is there some tricks in the OS configuration or in UHD configuration to
avoid that ?

Thanks in advance,

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