clock is drifting with timed commands

[alexeyzhuchkov]

I have observed drift in the fpga clock. I am using tags in GNU Radio to transmit a packet on every PPS. But when I see the PPS and packet on an Oscilloscope I see that the packet is continuously moving away from PPS. Sometimes it moves away faster some time slower. What could cause this? The PPS is coming from GPSDO firefly1-A.

We are using "tx_time" tags, used in GNU Radio, for controlled transmission. Tags are working but the clock is drifting. The packet is continuously moving away from the PPS.