Testbench 2

1
Testbench 2

• Lecture 30

2
Example

• Traffic light controller
• Input clock, reset and pedx
• Output car_light, ped_light
• State car_light
• Feature 1 If reset is high, car_light is red
• Set to state green, then reset
• Set to state yellow, then reset
• Set to state red, then reset
• Repeat for pedx low and high
• Repeat for a few clock cycles

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Feature 2

• If both reset and pedx are low, repeat green 100,
  yellow 10 and red 20
• Set to state red, then run for 500 cycles
• Set to state yellow, then repeat above ?
• Set to state red, then repeat above ?
• Try different clock rate
• Try race condition between reset low and clock

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Feature 3

• If reset is low and pedx is high
• If state is green, go to yellow
• Set to state green, then pedx
• Set pedx high at various time, duration
• If state is yellow, normal flow
• Set to state yellow, then pedx
• Set pedx high at various time, duration and
  multiple pedx
• If state is red, stay on red for 20 cycles
• Set to state red, then pedx
• Set pedx high at various time, duration and
  multiple pedx

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Verifying Output

• Automatic

traffic_light_controller c1 (clock, reset,
pedx, car_light, car_light) always begin
clock0 10 clock1 10 end initial begin
reset 1 pedx 0 1 if (car_light !
RED) display(error) end
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Exhaustive or Random

• Exhaust all input combinations
• Complete
• Time consuming
• Suitable for small modules
• Random input
• random(seed)

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Numerical Variables

• All boundaries
• if (x gt y)
• Try xy, xy1 and xy-1
• Also try max x and min x, max y and min y

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Explicit FSM

• Set to each state
• Using input to reach each state takes too long
• Use force-release
• Try each input combination
• Verify next state and output

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Algorithmic State Machines

• Walk though all paths of the algorithm
• Force each state and provide input
• Verify next state and output for each edge of the
  ASM
• Example (up_down_counter)

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Handshaking

• Verify each state machine independently
• Verify each edge of handshaking