Convert a Turnstile Protocol into an FSM
Problem
A turnstile starts LOCKED. A coin while LOCKED moves to UNLOCKED and pulses `unlock`. A push while UNLOCKED permits one passage, returns to LOCKED, and pulses `pass`. A push while LOCKED pulses `alarm`; a coin while UNLOCKED pulses `refund`. Coin and push high together are invalid and leave state unchanged while pulsing `alarm`. Design the state-transition diagram and implement the complete synchronous Moore-state/Mealy-pulse controller.
module turnstile(input logic clk,rst_n,coin,push,
output logic locked,unlock,pass,refund,alarm);
// coin/push are synchronous one-cycle events
// pulse outputs are one cycle; reset state is LOCKEDExample input and output
Use this case to check your interpretationCase 1: LOCKED + coin
Case 2: UNLOCKED + push
Case 3: Either state + coin=1,push=1Case 1: UNLOCKED, unlock=1, locked=0 on the updated state, all other pulses 0.
Case 2: LOCKED, pass=1, refund=alarm=unlock=0.
Case 3: state unchanged and alarm=1 only.The shown result follows by applying this rule: The diagram and RTL implement all state/event combinations including simultaneous invalid inputs. The cases also demonstrate this requirement: Default every pulse low each cycle, define no-event as state hold, and include illegal-state recovery to LOCKED with no transaction pulse.
Requirements (4)
- Use exactly two stored states, LOCKED and UNLOCKED; active-low reset enters LOCKED and clears all pulse outputs.
- Implement the four single-event transitions exactly as stated and drive `locked` directly from registered state.
- When coin and push are both high, keep the old state, pulse alarm only, and do not pulse unlock, pass, or refund.
- Default every pulse low each cycle, define no-event as state hold, and include illegal-state recovery to LOCKED with no transaction pulse.