On Wed, Nov 08, 2006 at 02:06:11PM -0800, Thomas Schmid wrote: > Hi all, > > I am currently trying to measure delays on the USRP and found some > interesting things. I wanted to see if others have similar results: > > - First I measured the round trip time of my IEEE 802.15.4 > implementation. I have to computers, one runs a ping application, the > other one a pong. The average delay in this case is 26.8ms. > > - Next, I measured the round trip time of my FSK implementation (also > based on packets). Here, the mean RTT is 14.9ms. > > - Next, I tried to find out the one way delay, i.e., how much time > does it take between generating one sample at the computer, until that > sample gets sent out at the USRP output. For this, I changed the code > of the sig_gen class such that it generates a square wave instead of a > cosine and I added code that toggles the parallel port pins according > to the state of the square wave. Then I used an oscilloscope to > measure the delay between the two signals, i.e., the one generated at > the parallel port and the one from the USRP (LFTX). The signal is at 2 > Hz. > The delays in this case depend a lot on what I choose for the > decimation (while keeping a constant square wave frequency). If I use > decimation=500, then I find an average delay of 65.8ms. When I change > the decimation to something else, I get values ranging from 30ms up > to 150/200ms (I didn't do exact measurements for these yet). > > What I am wondering is, why is there such a huge difference? Is it > because of the GNU Radio scheduler? Or is there some other problems? > > Thomas
Have you tried explicity setting the fast usb buffering? Take a look at the examples in gnuradio-examples/python/digital/*.py You want to pass the fusb_* args to the usrp constructor. Eric _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
