Re: [Discuss-gnuradio] Can not get rx time tags

[Josh Blum]

On 09/06/2013 08:08 PM, Gong Zhang wrote:
> Dear Josh,
>   Thanks for your reply.
>   I move the code "get_tags_in_range" in
> digital_correlate_access_code, so it will be executed when
> digital_correlate_access_code runs.
>   I start the sender first and then the receiver. But I still get no tag.
>   Does "the beginning of stream" mean the point just the receive program runs?

Well, when the USRP source block begins streaming, the very first sample
should have a time tag.

What blocks are in between USRP source and digital correlate access
code? The reason I ask, is that some block in the middle may not be
propagating tags. Which would explain the missing tags :-)

-josh

> 
> 2013/9/5 Josh Blum <address@hidden>:
>>
>>
>> On 09/03/2013 12:41 AM, Harry Zhang wrote:
>>> Hi,
>>> I'm trying to get rx time tags in narrowband Benchmark_tx/rx with a
>>> modified digital_correlate_access_code.cc. But the
>>> "get_tags_in_range(rx_time_tags,0,this->nitems_read(0)+i,this->nitems_read(0)+i+1,pmt::pmt_string_to_symbol("rx_time"))"
>>>
>>> method gets no tag in rx_time_tags while the communication between two
>>> USRP N210s running benchmark_rx/tx is OK.
>>> I'm using GNU Radio 3.6.5.1, Ubuntu12.04, boost 1.48 and UHD 3.5.3.
>>> Thanks in advance.
>>>
>>
>> The time tag is sent once at the beginning of streaming and after
>> overflows. Its not necessary to send more time tags because the absolute
>> sample count and sample rate can be used to interpolate the time to any
>> sample.
>>
>> So I think are you seeing a time tag, just only once at init time. When
>> the block sees the time, try to save the timestamp and the count it was
>> found at.
>>
>> I hope that helps!
>> -josh
>>
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