[Discuss-gnuradio] delay through dsp pipeline

[Pham, Thanh]

Hello,

In several discussions, I recall it was mentioned that the timestamp reference is at the end of the dsp pipeline. Is the dsp pipeline consisting just of the DDC or anything else? 

It was also mentioned that the delay through the dsp pipeline depending on some factors such as decimation rate. If we have multiple usrps2 using the same decimation rate, center freq, what other factors would contribute to the difference in arrival of the signal at the end of the dsp pipeline? (if two usrps2 are receiving from the same antenna and using a 10MHZ gps reference signal).

Is there a way to figure out the delay from the ADC to end of the dsp pipeline?

I also saw a mention about a patch for the start_rx_stream_at, which tells the usrps2 to start streaming at a specific time. Can someone elaborate on that some more? Whose time does the usrp2 based on to do that, and does that ensure two usrp2 start streaming at the same time?

Thanks for any inputs!

Thanh