Also, you could do a quick test on DSP side, just write more data to UART port than the baud rate can handle and see what the write() function returns and how much time it takes. Usually the write() function is non-blocking, as it will hand off data to underlying layers to take care of UART writing. But I suspect that if the SDSP UART system runs out of buffers to put your data in, it will probably block until buffer space for writing frees up instead of dropping data. I have not confirmed this, but that's my expectation.