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

[Josh Blum]

On 01/07/2013 04:46 PM, LD Zhang wrote:
> Thanks to Josh and Marcus for their comments. The set_time_now command
> works! After I put it in, the earlier observed 0.5 sec offset between the 2
> USRP became ~0.1 second. So there is still work to do. I guess my options
> are:
> 
> 1. Make the set_start_time command to work. My question is how I can make it
> work in python. I hand edited the set_time_now command to embed in the
> initialization part of the top_block.py code generated from GRC (which has
> worked). Do I just hand edit the set_start_time just following that command?
> Now the problem is that after set_time_now, the USRP time is sync'd to the
> system time. But what is the argument I should give to set_start_time?
> 

Just a time in the near future that you can reasonably schedule in
advance of starting the flow graph. Like:
uhd.time_spec(time.time() + 0.5))

> 2. The other option is to get the metadata out for the samples collected.
> From what I read, it looks like one cannot do it in GRC, but have to edit
> the cpp source code. Is there an example somewhere of how this is done?
> 

you can write a custom block in c++ or python to deal with tags

The most complete guide is here, but it requires installing grextras. I
think you can do this w/ more recent native gnuradio, but there isnt a
guide yet

https://github.com/guruofquality/grextras/wiki/Blocks-Coding-Guide#wiki-stream-tags

-josh

> Thanks very much,
> 
> LD
> 
> -----Original Message-----
> From: LD Zhang [mailto:address@hidden 
> Sent: Friday, January 04, 2013 5:38 PM
> To: 'Marcus D. Leech'; 'address@hidden'
> Subject: RE: [Discuss-gnuradio] How do I capture of the time of USRP N210
> samples with host computer system time?
> 
> Great! Thanks. I tried to import time and it works. Now I just have to see
> if this is sufficient for my sample gather timing or I still have to get the
> timestamp of the first sample using metadata and such.
> 
> LD
> 
> -----Original Message-----
> From: Marcus D. Leech [mailto:address@hidden
> Sent: Friday, January 04, 2013 4:15 PM
> To: LD Zhang; address@hidden
> Subject: Re: [Discuss-gnuradio] How do I capture of the time of USRP N210
> samples with host computer system time?
> 
> On 01/04/2013 07:03 PM, LD Zhang wrote:
>> Hello,
>>
>> I tried the following command in python:
>>
>>> python:
>>> usrp_source.set_time_now(uhd.time_spec_t(time.time())
>>>
>> It doesn't seem to work. Looks like the "time.time()" is wrong? Looked 
>> up an earlier example:
>>
>> set_time_now(uhd::time_spec_t(0.0), 0)
>>
>> The syntax looks different. But this may be doing something different 
>> from my intention which is to sync the USRP time to the host system 
>> time. I am still searching for the right syntax for this command. Any 
>> help is appreciated.
>>
>> LD
>>
>>
>>
>> _______________________________________________
>> Discuss-gnuradio mailing list
>> address@hidden
>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>
>>
> You'll have to put an:
> 
> import time
> 
> In your python
> 
> 
> 
> --
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortium
> http://www.sbrac.org
> 
> 
> 
> 
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