Re: [Discuss-gnuradio] Time Granularity of USRP N2XX

Dear Marcus,
Thank you for your reply.
I'm confused about two concepts. Referring to the file
time_spec.hpp in UHD, fractional sec is calculated according to the
parameter ticks and tick_rate. So I think the time granularity is
'1/tick_rate' which is 0.1us using 10Mhz clock. But for the timestamp
of sample stream, the granularity is the sample duration. Is it correct?

Best,
Harry
2013/11/26 20:12, Marcus Müller wrote:
> Hi Harry,
>
> as far as I know, the granularity of a time stamp is the sample
> duration at the downsampled side.
> As for the 10MHz: The 10MHz clock is used to derive different other
> clocks, especially the rx ADC and tx DAC clocks, which are an order of
> magnitude higher; bear in mind that when you request e.g. "5MHz samle
> rate" you still get the 100MHz* samples of the ADC, but downsampled by
> a factor of 20.
>
> Please also bear in mind that due to physics, processing etc the
> timestamp of the rx side is delayed to the actual reception of "that
> sample", and that this delay is largely constant when receiving using
> the same settings, but my change based on sampling rate and other
> factors.
>
> Greetings
> Marcus
>
> *for USRP2 arch, if I remember correctly.
> On 26.11.2013 13:04, Harry Zhang wrote:
>> Hi,
>> Since we can get receive time of rx_stream's first sample via rx tags, I
>> have two questions about the time granularity. Given the internal clock
>> is 10Mhz, is the time granularity 0.1us? The fractional second is stored
>> double type. Does it mean the last digits of the fractional sec are
>> invalid?
>>
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