How to use enable_rx_timestamps()?

[tomwts]

I want Tx radio begins transmitting about 1/4 sec after Rx radio starts streaming samples to DDC and dmaFIFO to simulate a RF path delay. After enable_rx_timestamps() is added to my app, the Tx radio block no longer sends data. Instead, I got a bunch of "L" errors printed on the console. I thought by setting a 1/4 sec delay in the issue_stream_cmd(), it would be sufficient to cause the received samples saved in the FIFO until Tx radio is unblocked, but it didn't work.

Some of the UHD 4.7 release example app like rfnoc_radio_loopback has rx-timestamps command line option, but enabling it resulted in getting numerous "L" errors and the Tx radio block couldn't send any data.

How enable_rx_timestamps() works and how to use it properly?

Thanks,