Additional to the UDP messages, and OSC messages, the Start, Stop and Resume action can also be given with buttons.
The mapping is as following:
GPIO2 -> Start action [Button <START>]
GPIO3 -> Stop action [Button <STOP>]
GPIO6 -> Resume action [Button <RESUME>]
The GPIO pins are active low (connecting the other side of the button to ground). See also here.
The mapping for the buttons is as following:
GPA2 -> Button <SELECT>
GPA3 -> Button <BACKWARD>
GPA4 -> Button <FORWARD>
GPA5 -> Button alt_function=0 <START/RESET>, alt_function=1 <START/RESUME>
GPA6 -> Button <STOP>
GPA7 -> Button alt_function=0 <RESUME>, alt_function=1 <RESET> --> confirmation with <SELECT>
The GPA pins are active low (connecting the other side of the button to ground).