Modes of operation:

BOARD_RUN
The motors are set to move automatically based on the physics algorithm. LEDs reflect battery status. Enabled interrupts are only:
	IMU (timer) interrupt
	PWM interrupt
	Hall sensor interrupt
	(in emergency) watchdog interrupt
Main loop handles stopping (BOARD_RUN->BOARD_STOP, on stopping after certain velocity attained, or on high sideways tilt at low speed) and safety

BOARD_STOP
Default condition on startup. The motors are isolated from the power supply. LEDs reflect battery status. Enabled interrupts are only:
	IMU (timer) interrupt -> calculate tilt angle as usual
	Hall sensor interrupt -> update e_theta only (updating the speed variables requires a rotating motor!)
	(in emergency) watchdog interrupt
Main loop handles starting (BOARD_STOP->BOARD_RUN, on observed tilt angle around zero (flat) for a few seconds) and setup (BOARD_STOP->BOARD_SET, on button press/no prox) and safety

BOARD_SET
This allows selection of particular setup routines using buttons. The motors are isolated. Enabled interrupts are only:
	(emergency) watchdog interrupt
Main loop handles button inputs to select menu 1-4 and item 1-4, LEDs reflect the selection.
Menus/items
	1. Safe modes
		1. No limiting (full power)
		2. Torque (current) limit to 20%
		3. Velocity (voltage) limit to 20%
		4. Velocity and torque limit to 20%
	2. Data logging
		1. Log IMU data
		2. Log currents and battery voltage
		3. Log temperature
	3. Calibration
		1. Hall sensor offset calibration (-> BOARD_HALL_CAL)
		2. Current sensor calibration
		3. IMU calibration

BOARD_HALL_CAL
Hall sensor calibration. This spins each motor at a known slow speed (assuming no load) and uses special hall sensor interrupt to average and store e_theta at each reading change.
Enabled interrupts:
	Hall sensor calibration interrupt - averages and stores readings
	PWM calibration interrupt - makes PWM cycles given a particular e_theta and voltage (rather than current -> runs open loop)
	(in emergency) watchdog interrupt
LEDs reflect status of calibration. On exit goes to BOARD_STOP.

BOARD_CUR_CAL
Current sensor calibration. This sets a given PWM cycle on each of the measured phases, so a current can be measured across a resistor to V-. Buttons determine the PWM cycle and are used to set the cycle which gives a particular current reading (such as 1A, 2A, 5A, etc).
Enabled interrupts:
	PWM calibration interrupt 2 - makes a PWM cycle given a particular duty cycle and phase - open loop and not for motor control
	(in emergency) watchdog interrupt
LEDs reflect status of calibration. Buttons control current. On exit goes to BOARD_STOP.

BOARD_IMU_CAL
IMU Calibration. This reads the IMU when it is still and sets the required offset parameters.
Interrupts:
	IMU calibration interrupt
	(in emergency) watchdog interrupt
LEDs reflect status of calibration. On exit goes to BOARD_STOP.