[Discuss-gnuradio] High CPU load when sending waveform from file to USRP2

[Jakob Meineke]

Hi all,

 

I use USRP2 to generate some RF signal around 60 MHz using a script that is a slight modification of usrp2_siggen.py. I first create the signal on the host, write it into a file sink and when the calculation is done I use the same file as a signal source and send it to the USRP2. At this point I do not understand why this process uses between 80% and 100% of one CPU. Whenever the CPU load gets too close to 100% I observe the otherwise nice peak at say 60MHz becomes very broad and noisy which renders it useless for my application. The load gets close to 100% reliably when the CPU is switched, but also on its own. The steps in the quality of the signal are discrete, it is either very nice or very bad. The computer is a fairly new one (HP Compaq de7800p), Intel Core Duo 3.16 GHz, 2 GB RAM running Ubuntu 8.10. I upgraded today to the latest gnuradio version from the trunk and recompiled the firmware. The USRP2 is hooked to the onboard Gigabit Ethernet.

When I do not enable realtime scheduling in the script the CPU load seems to increase even more and the signal is never nice. The sampling rate is 10e8/4, where 4 is the interpolation set in siggen.py. Using an interpolation of 8 seems to alleviate the problem but I need the bandwidth. I installed the realtime kernel which did not change a thing.

I would very much appreciate any hints on how to understand this or on what I am missing. I do not understand why the CPU load is so high when the calculation is already done and only the file has to be read. Cheers,

 

JJM