I am currently investigating different USRP delays. Some of them I can explain, others not. For example, I see an average delay of 6.2ms while receiving data from the USRP at a sample rate of 8MHz (short real samples, i.e. I am using the usrp.source_s). Here is my setup: - I have a function generator which generates a 1Hz square wave. This signal is fed into a LFRX on the USRP and into CH1 of an oscilloscope. - On the PC side, I modified the null sink to check for a pos/neg signal (with some thresholding). When the signal is high, I output 1 on the parallel port, when it is low, I output 0. The parallel port is also hooked up to the Oscilloscope. This allows me to measure the delay between the two signals. - I usefusb_block_size=512, fusb_nblocks=1
Here are some numbers I got: - decimation 8: mean delay 6.1ms - decimation 32: mean delay 6.4ms - decimation 64: mean delay 4.3ms - decimation 256: mean delay 14.7ms First of all, I don't understand why we have such a high delay. Shouldn't it be more in the hundreds of /mu s instead of in the ms range? Second, why is the delay shorter for decimation 64, and again larger for a decimation of 256? Thomas _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
