USRP transmitting timestamp


I want to transmit a frame from a USRP to another USRP.

I think that is a packed based transmitting.

is there any method to get the transmitting timestamp of USRP sink?

I check the

there is the “_metadata.time_spec”, it will update by the num_sent and
the samp_rate.

but if my flow is not continuous…

so that the time is invalid… due to the time not keep updating.

or is there any method about making the frame along with a continuous

to make the stream continuous and i can get the valid timestamp.

Thank you so much!!