USB latency & fx3 firmware loopback
Posted: Sun Feb 24, 2019 3:03 pm
Hi,
I am trying to measure USB30 latency in my PC. To do so I created grc flow to calculate cross-correlation on a stream that splits and goes through the FX3 firmare loopback - the idea follows the http://www.philipzucker.com/gnuradio-delay-correlation/ and in general it works, but I don't get any reasonable results.
No matter what I do I see no delay between osmocom-Sink and osmocom-Source in firmware loopback mode - at least no delay in single us range. Even when I connect dual input GUI Time Sink to Sink input and Source output the streams are identical. At 8Msps that would mean that round trip of the signal thgough fx3 is below 0.5 sample (I guess) - so like tens of nanoseconds. Kind of hard to believe.
Changing loopback to "bb" makes some difference, but I wanted to avoid scaling & filtering needed when signals go thought ADC. I feel like I am missing some major information here either on how GRC works or how samples flow in firmware loopback mode. Could someone let me know if the firmware loopback mode is really in FX3 on the bladeRF board?
thanks
b.r.
I am trying to measure USB30 latency in my PC. To do so I created grc flow to calculate cross-correlation on a stream that splits and goes through the FX3 firmare loopback - the idea follows the http://www.philipzucker.com/gnuradio-delay-correlation/ and in general it works, but I don't get any reasonable results.
No matter what I do I see no delay between osmocom-Sink and osmocom-Source in firmware loopback mode - at least no delay in single us range. Even when I connect dual input GUI Time Sink to Sink input and Source output the streams are identical. At 8Msps that would mean that round trip of the signal thgough fx3 is below 0.5 sample (I guess) - so like tens of nanoseconds. Kind of hard to believe.
Changing loopback to "bb" makes some difference, but I wanted to avoid scaling & filtering needed when signals go thought ADC. I feel like I am missing some major information here either on how GRC works or how samples flow in firmware loopback mode. Could someone let me know if the firmware loopback mode is really in FX3 on the bladeRF board?
thanks
b.r.