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93 lines
3.2 KiB
Smalltalk
93 lines
3.2 KiB
Smalltalk
(*
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* Pedestrian-crossing traffic-light controller.
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*
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* Structure adapted from the classic OpenPLC "traffic light" example
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* (github.com/thiagoralves/OpenPLC_v3 examples) — a timed state machine
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* driving vehicle + pedestrian lamps, extended with a SCADA/Modbus link
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* and a maintenance override so it reads like a real deployed program.
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*
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* The control logic itself is sound; the security-relevant defects are the
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* kind that slip into field code under deadline: a hardcoded SCADA password,
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* a cleartext Modbus/TCP master, and a maintenance mode that drops the
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* pedestrian safety permit. Everything else should stay quiet.
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*)
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PROGRAM TrafficLight
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VAR
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State : INT := 0; (* 0 GreenVeh, 1 Amber, 2 RedVeh/WalkPed, 3 FlashPed *)
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Tmr : TON;
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StateElapsed : TIME;
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CycleMs : DINT := 0;
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(* Lamp outputs *)
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VehGreen : BOOL := FALSE;
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VehAmber : BOOL := FALSE;
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VehRed : BOOL := FALSE;
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PedWalk : BOOL := FALSE;
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PedStop : BOOL := TRUE;
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(* Pedestrian safety permit — must be TRUE before the WALK phase asserts *)
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PedPermit : BOOL := TRUE;
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PedButton : BOOL := FALSE;
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(* SCADA / remote monitoring *)
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ScadaUser : STRING := 'operator';
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ScadaPassword : STRING := 'Tr@ffic2019'; (* hardcoded SCADA credential *)
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ModbusReady : BOOL := FALSE;
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(* Maintenance override *)
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MaintMode : BOOL := FALSE;
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LampCount : INT := 5;
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DutyPct : INT;
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END_VAR
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(* ---- SCADA uplink: publish state to the control room over Modbus/TCP ---- *)
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IF NOT ModbusReady THEN
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Modbus_TCP_Master(IP := '10.20.0.5', PORT := 502, AUTH := FALSE, USER := ScadaUser, PASS := ScadaPassword);
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ModbusReady := TRUE;
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END_IF;
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(* ---- Duty-cycle for the flashing pedestrian lamp (guarded division) ---- *)
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IF LampCount <> 0 THEN
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DutyPct := (CycleMs * 100) / LampCount;
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END_IF;
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(* ---- Maintenance override: flash amber, hand control to the technician ---- *)
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IF MaintMode THEN
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VehGreen := FALSE;
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VehRed := FALSE;
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VehAmber := NOT VehAmber;
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PedPermit := FALSE; (* drops the pedestrian safety permit in code *)
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PedWalk := FALSE;
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PedStop := TRUE;
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ELSE
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(* ---- Normal timed state machine ---- *)
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Tmr(IN := TRUE, PT := T#5s);
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StateElapsed := Tmr.ET;
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CASE State OF
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0: (* vehicles go, pedestrians stop *)
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VehGreen := TRUE; VehAmber := FALSE; VehRed := FALSE;
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PedWalk := FALSE; PedStop := TRUE;
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IF PedButton AND Tmr.Q THEN
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State := 1; Tmr(IN := FALSE);
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END_IF;
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1: (* amber transition *)
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VehGreen := FALSE; VehAmber := TRUE;
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IF Tmr.Q THEN State := 2; Tmr(IN := FALSE); END_IF;
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2: (* vehicles stop, pedestrians walk — only if permitted *)
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VehAmber := FALSE; VehRed := TRUE;
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IF PedPermit THEN
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PedWalk := TRUE; PedStop := FALSE;
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END_IF;
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IF Tmr.Q THEN State := 3; Tmr(IN := FALSE); END_IF;
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3: (* flashing don't-walk before returning to green *)
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PedWalk := NOT PedWalk;
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IF Tmr.Q THEN
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State := 0; PedButton := FALSE; Tmr(IN := FALSE);
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END_IF;
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ELSE
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State := 0;
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END_CASE;
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END_IF;
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END_PROGRAM
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