[USRP-users] RFNoC timing clarification

Jason Matusiak jason at gardettoengineering.com
Wed Jul 12 13:03:50 EDT 2017


Howdy Jonathon!

Is a "packet" determined before or after the RFNoC stage of the chain (I 
assume before since it is in the radio core)?

Is there anyway to modify things if I decide to resample in an RFNoC 
block?  It seems like it would throw off the timing since the sample 
rate into the block != the sample rate leaving the block in this case.

~Jason


On 07/12/2017 12:58 PM, Jonathon Pendlum wrote:
> Hey Jason,
>
> The timestamp of each packet describes the time the first sample in 
> the packet was received. The timestamp is based on a counter in 
> noc_block_radio_core (timekeeper.v.) that increments at the sample 
> rate (i.e. radio_clk). The time is relative to that counter's 
> placement in the processing chain. We do not do anything to back out 
> the delays from elements in front of the counter, such as the delay 
> through the front end filters, ADC, digital I/Q correction, etc.
>
> Jonathon
>
> On Wed, Jul 12, 2017 at 9:20 AM, Jason Matusiak via USRP-users 
> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
>
>     I have a timing question that has me going in circles, I don't
>     understand how the USRP timestamps work when using RFNoC.
>
>     In a normal system, packets have timestamps with them (or at least
>     the first one does) and you can compute the time of any samples
>     based on the timestamp, sample rate, and number of samples since
>     the timestamp, right?
>
>     Now, if I am using RFNoC, the timestamps aren't attached to the
>     samples, right?  Where does that timestamp get associated: 
>     Further down the stream?
>
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