Re: [Discuss-gnuradio] rx_timed_samples.cc doesn't stop streaming of samples

[Josh Blum]

> Couple more questions if you don't mind:
> 1) Where does the number of items per packet (which is 365 in my case) comes
> from? Or is it the format USRP2 always uses to send the data to the host?

Its probably the MTU (1500 bytes) minus the ip/udp/ethernet headers 
sizes minus the size of the vrt headers. Basically, the maximum number 
of samples per frame.

> 2) After specifying -N as 1000 I got the following output:
>
> Got packet: 1267693414 secs, 35564266 ticks
> Got packet: 1267693414 secs, 35570106 ticks
> Got packet: 1267693414 secs, 35575946 ticks
>
> So the number of ticks between the packets is 5840, dividing by 365 we get
> 16-the number of ticks per sample, and the decimation is 16 which is
> consistent. My question is: if I want to extract the timestamps for each
> sample individually I would need to take the timestamp of the packet and
> subtract the required number of 16*N (e.g. for the sample number 300 in the
> first packet the timestamp is 35564266-65*16=35563226) or is there a
> different way the get hold of timestamps for individual samples?

That's correct:
The Nth sample will be N*usrp2_clock_rate/samp_rate ticks offset from 
the timestamp or in this case N*16 ticks offset. Each sample has a 
temporal ambiguity equal to the width of 16 clock ticks.

-Josh