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.

Updated state diagram

%%{init: {'theme':'dark'}}%%
stateDiagram-v2
	[*] --> Base : reset
	Base --> WaitForDroplet: droplet_acquisition_enable
	state WaitForDroplet {
		state if_state_1 <<choice>>
		[*] --> ReadADC_1
		ReadADC_1 --> if_state_1
		if_state_1 --> ReadADC_1 : if ADC < min_intensity
		if_state_1 --> Reset_droplet_width_counter: if value >= min_intensity
		Reset_droplet_width_counter --> Update_droplet_intensity_max_1 
		Update_droplet_intensity_max_1 --> [*]
	}

	WaitForDroplet --> AcquiringDroplet : if ADC >= min_intensity
	state AcquiringDroplet {
		state if_state_2_1 <<choice>>
		state if_state_2_2 <<choice>>
		[*] --> ReadADC_2
		ReadADC_2 --> Increment_droplet_width_counter
		Increment_droplet_width_counter --> if_state_2_1
		if_state_2_1 --> if_state_2_2: if ADC <= droplet_intensity_max
		if_state_2_1 --> Update_droplet_intensity_max: if ADC > droplet_intensity_max
		Update_droplet_intensity_max --> if_state_2_2
		
		if_state_2_2 --> [*]: if ADC <= min_intensity
		if_state_2_2 --> ReadADC_2: if ADC > min_intensity
	}

	AcquiringDroplet --> EvaluateDroplet : if ADC < min_intensity
	state EvaluateDroplet {
		[*] --> IncrementCounters
		IncrementCounters --> Set_droplet_classification
		Set_droplet_classification --> [*]
	}

	state if_state_sorting <<choice>>
	EvaluateDroplet --> if_state_sorting
	if_state_sorting --> Base : if not sorting_enabled
	if_state_sorting --> SortingDelay : if sorting_enabled

	state SortingDelay {
		state if_state_4 <<choice>>
		[*] --> Update_sort_delay_counter
		note right of Update_sort_delay_counter
			Reset sort_delay_counter to 1 if entering SortingDelay state
			Otherwise increment sort_delay_counter
		end note
		Update_sort_delay_counter --> if_state_4 
		if_state_4 --> Update_sort_delay_counter : if sort_delay_counter < sort_delay
		if_state_4 --> [*] : if sort_delay_counter >= sort_delay
	}

	SortingDelay --> Sorting
	state Sorting {
		state if_state_5 <<choice>>
		[*] --> Enable_sort_trig
		Enable_sort_trig --> Update_sort_counter
		note right of Update_sort_counter
			Reset sort_counter to 1 if entering Sorting state
			Otherwise increment sort_counter
		end note
		Update_sort_counter --> if_state_5
		if_state_5 --> Update_sort_counter : if sort_counter < sort_duration
		if_state_5 --> Disable_sort_trig : if sort_counter >= sort_duration
		Disable_sort_trig --> [*]
	}
	
	Sorting --> Base	

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