State Machine

The FADS State Machine

To implement the droplet sorting functionality a so called state machine was used. The concept relies on states that perform actions and specific conditions that determine when a transition from one state into another should happen.

The FADS state machine has the following six states depicted in the UML diagram.

Note that the states also correspond to the equally numbered LED on the RedPitaya, where the state can be notified visually in real-time.

State 0 - Base State

• On fads_reset
  • regardless of the current state, fads_reset will always land here.
  • resets all counters to 0
• Waits for droplet_acquisition_enable

State 1 - Waiting for Droplet

• Waits until intensity rises over min_intensity_threshold
• Starts droplet acquisition once intensity is reached

State 2 - Droplet Acquisition

• Updates droplet_intensity_max with new maximum intensity values for this droplet
• Continually increments droplet_width_counter for this droplet
• Until intensity falls again below min_intensity_threshold

State 3 - Droplet Evaluation

• increments the respective counters for positive/negative, long/short and high/low intensity droplets
• updates the output registers with droplet_id, cur_droplet_intensity and cur_droplet_width
  • keep logging caveats in mind!
• starts sorting delay

State 4 - Sorting Delay

• Variable delay (sort_delay) until droplet reaches sorting junction

State 5 - Sorting

• Activates sort_trig for a variable duration (sort_duration)

The sort_trig signal can be used by the asgs widget as a trigger source called fads to turn on the signal generator for the duration.