Please write the VHDL code for incorporating this:
You are asked to implement a timer with the following list of requirements:
1. Implemented on the Basys3 board with VHDL.
2. Responds to input from photodiode sensor pairs to start and stop the timer.
3. Displays time elapsed in decimal values.
4. Continues to display the last time value after the stop input.
5. Reset by a push button on the Basys3 board.
