add the timer function for timestamping purpose

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Capture the timestamp in ms

Print to UART for debugging purpose, especially to study the Matlab
execution between one transmit to another.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>