On the ATmega128RFA1, SNAP uses Timer 2 and Timer 4 internally.
Timer 2 is used for timed sleep and can be reused by the user if the node will not be using timed sleep. Timer 4 provides the 1 millisecond “heartbeat.”
Do not peek()/poke() these timers!
The remaining timers are available for use by your scripts (for example, PWM).