I think I have solved my own question.
The USART Tx data register is double buffered so the DMA will *think* it has finished the transfer but in reality there are still two bytes in the USART Tx data register that still need to be shifted out.
I think I have solved my own question.
The USART Tx data register is double buffered so the DMA will *think* it has finished the transfer but in reality there are still two bytes in the USART Tx data register that still need to be shifted out.