GNU Radio sink question

[address@hidden]

I have just completed gr-rpitx a GNU Radio sink block for emitting
from Raspberry Pi's GPIO output thanks to F5OEO's librpitx 
(https://github.com/jmfriedt/gr-rpitx) and the dataflow is well scheduled 
as shown with the short movie 
https://github.com/jmfriedt/gr-rpitx/tree/main/examples/gr-rpitx_demo.mp4

However in this implementation, GNU Radio Companion complains that I have
not included a Throttle block since it does not know that the sink is clocked
by hardware. How can I tell GNU Radio that the stream data rate will be defined
by this hardware sink ?

Thanks, JM