How to implement the transfer of one byte to uart upon arrival of SOF?

Question

Microcontrollers

I am creating a project in CubeMX for TrueStudio, class usbaudio full speed. The device (stm32f103c8t6) is detected in windows, shows that the sound is being played.
Tell me in which function to insert the @ line of sending a byte to uart @ so that the byte is sent with the arrival of SOF (it should come 1000 times per second)

Answer 1

use the send one byte function.
it must be mandatory, because the function of sending a string of bytes is formed from it.