Hello
I apologize for the delayed answer, I suggest you use the function USART_TransferSendNonBlocking, This function sends data using an interrupt method. This is a non-blocking function, which returns directly without waiting for all data to be written to the TX register. When all data is written to the TX register in the IRQ handler, the USART driver calls the callback function and passes the ref kStatus_USART_TxIdle as status parameter.
Let me know if this is helpful, if you have more questions do not hesitate to ask me.
Best regards,
Omar