So what does all that stuff do?
It reads the switches, shows the values on the display, updates the Left and Right volume registers in the volume chip and finally goes to sleep when nothing happens for ~20 seconds. Nothing in the way of button presses that is.
If you want to wake the system up, you press the right hand button.
The system has 3 operating modes. You can adjust the left, right or both volumes simultaneously. Righthand button is up, lefthand button...