SM Software

ability to reprogram controller over ASYNC serial
2 DMA controllers run the two ADC units at 12 bits, 400 KHz total sample rate
Input capture measures PWM period of magnetic rotary encoder / QEI captures encoder position
DMA controller sends/receives SPI to digital accelerometer
Main code loop runs at 500 Hz
- decimation of analog inputs
- reads ankle position
- reads IMU, estimates orientation
- reads motor controller status (motor current, motor position, status)
- processes external communication interface

deep sleep / sleep / initialization

when entering a sleep state, some parameters may be written to EEPROM. Specifically the SG offsets will be checked against the stored value, and updated if the offset changes "significantly".

(<10uA, <0.25uW) when battery is near death. Disconnect as much of the system as possible from battery.
motor leads are shorted with "zero power"

the motor controller is is very lower power state (only activity is listen on Rx), motor leads shorted

On SM only the accelerometer is active (all other sensors are unpowered)
- the accelerometer is programmed to generate an interrupt on certain acceleration conditions
- the CPU will periodically (10Hz) awake and check the state of the accelerometer and conditionally enter a "mid-power" state to test other sensors.
- if sensors suggest the ankle is active, the initialization state is entered

state entered upon connection of battery is attached or when waking from sleep
all sensors and hardware are powered, but motor leads remain shorted
SM will watch for a transition from ankle on ground (loaded) to ankle in the air.
- shortly after ankle in the air the K3 strap will force the ankle into the zero position. The set point for the virtual spring is zeroed to this location
- A small (1amp) current can be used to further guarantee the ankle is against the K3 strap.
- strain gauges offsets can be zeroed at this point.
- At this point the motor controller is commanded to enter current mode and the SM proceeds to normal operational mode.

ability to reprogram controller over ASYNC serial
low power mode (5mW) where controller responds to ASYNC serial
- PWM off
- hall sensors periodically powered and monitored
- encoder power off,
standby (<<5mW) by where processor sleeps, wakes on serial RX
- all sensors and outputs are off
- motor leads are shorted