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.

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
• 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.