Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?

[Josh Blum]

On 01/16/2013 03:37 PM, LD Zhang wrote:
> Hi Folks,
> 
> Sorry for trying to resurrect this topic thought to be settled at one time.
> My earlier impression was somehow incorrect. Let me summarize the
> situation: basically one wants to gather data at approximately the same
> time for 2 USRPs. Using the 2 host computers sync'd to NTP, this appears to
> be feasible in principle. If they differ by 1 or 2 ms, I don't care and
> it's within tolerance of the particular application.
> 
> So the quickest thing to do was to modify the top_block.py generated from
> GRC as follows:
> 
> 
> self.uhd_usrp_source_0.set_time_now(uhd.time_spec_t(time.time()))
> 
> self.uhd_usrp_source_0.set_start_time(uhd.time_spec_t(time.time() + 0.5))
> 

How are you communicating the same start time to each device in your
setup? Suppose there were two devices, would it not be more like this:

self.uhd_usrp_source_0.set_time_now(uhd.time_spec_t(time.time()))
self.uhd_usrp_source_1.set_time_now(uhd.time_spec_t(time.time()))

#start stream time common for all N devices
start_time = uhd.time_spec_t(time.time() + 0.5)

self.uhd_usrp_source_0.set_start_time(start_time)
self.uhd_usrp_source_1.set_start_time(start_time)

-josh