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LSD account for train arrival-departure protocol

LSD account for a train arrival-departure protocol

/*****************************************************************************
file : train.lsd
date : 12/14/94
author : Simon Yun Pui Yung ('modernised' by wmb)
notes : description of agents for a `railway arrival-departure' system
******************************************************************************/
The stationmaster
agent sm() {

oracle (time) Limit, Time, // knowledge of time to elapse before departure due
(bool) guard_raised_flag, // knowledge of whether the guard has raised his flag
(bool) driver_ready, // knowledge of whether the driver is ready
(bool) around[d], // knowledge of whether there's anybody around doorway
(bool) door_open[d]; // the open/close status of door d (for d = 1 .. number_of_doors)

state (time) tarrive = |time|, // the S-M registers time of arrival
(bool) can_move, // the signal observed by driver for starting engine
(bool) whistle = false, // the whistle is not blowing
(bool) whistled = false, // the whistle has not blown
(bool) sm_flag = false, // S-M lowers flag
(bool) sm_raised_flag = false; // S-M has not raised flag

handle (bool) can_move,
(bool) whistle,
(bool) whistled,
(bool) sm_flag,
(bool) sm_raised_flag;
(bool) door_open[d]; // the open/close status of door d (for d = 1 .. number_of_doors)

derivate
number_of_doors
(bool) ready = /\ (!door_open[d]); // are all doors shut?
d = 1
(bool) timeout = (Time - tarrive) > Limit; // departure due

protocol
door_open[d] ^ !around[d] -> door_open[d] = false; (d = 1 .. number_of_doors)
ready ^ timeout ^ !whistled -> whistle = true; whistled = true; guard(); whistle = false;
ready ^ whistled ^ !sm_raised_flag -> sm_flag = true; sm_raised_flag = true;
sm_flag ^ guard_raised_flag -> sm_flag = false;
ready ^ guard_raised_flag ^ driver_ready ^ engaged ^ !can_move -> can_move = true;

}

The guard
agent guard() {

oracle (bool) whistled, sm_raised_flag, brake;

state (bool) guard_raised_flag = false,
(bool) guard_flag = false,
(bool) brake;

handle (bool) guard_raised_flag, guard_flag;

derivate LIVE = engaging || whistled;

protocol
engaging -> brake = true; running = false;
sm_raised_flag ^ brake -> brake = false; guard_flag = true; guard_raised_flag = true;
guard_flag ^ !sm_flag -> guard_flag = false;

}

The driver
agent driver() {

oracle (bool) can_move, engaged, whistled;
(position) at, from;

handle (position) to, from,
(bool) running,
(bool) driver_ready = false;

state (bool) driver_ready = false,
(position) from;

protocol
whistled ^ !driver_ready -> driver_ready = true;
engaged ^ from <> at -> from = at; to = next_station_after(at);
can_move ^ engaged -> driver_ready = false; running = true;

}

The passenger
agent passenger((int) p, (int) d, (position) _from, (position) _to) {
// passenger p intending to travel from station _from to station _to
// and he will access through door d of the train

oracle (position) at,
(bool) door_open[d];

state (bool) pos[p] = OUT_DOOR, alighting[p], boarding[p], join_queue[p,d];

handle (position) from[p] = _from;
(position) to[p] = _to;
(int) door[p] = d;
(bool) pos[p],
(bool) door_open[d];

derivate
alighting[p] = at == to[p] ^ pos[p] != OUT_DOOR && engaged;
boarding[p] = at == from[p] ^ pos[p] != IN_DOOR && engaged;
join_queue[p,d] = (alighting[p] ^ door_open[d] ^ pos[p] == IN_DOOR) ||
(boarding[p] ^ door_open[d] ^ pos[p] == OUT_DOOR);
LIVE = !(at == to[p] ^ pos[p] == ON_PLATFORM);

protocol
at == to[p] ^ pos[p] == AT_SEAT -> pos[p] = IN_DOOR;
alighting[p] ^ !door_open[d] -> door_open[d] = true;
alighting[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ !queuing[d]
-> pos[p] == OUT_DOOR; door_open[d] = false; pos[p] = ON_PLATFORM;
alighting[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ queuing[d]
-> pos[p] == OUT_DOOR; pos[p] = ON_PLATFORM;
boarding[p] ^ !door_open[d] -> door_open[d] = true;
boarding[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ !queuing[d]
-> pos[p] = IN_DOOR; door_open[d] = false; pos[p] = AT_SEAT;
boarding[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ queuing[d]
-> pos[p] = IN_DOOR; pos[p] = AT_SEAT;

}

The train
agent train() {

state (bool) running = true,
(bool) brake = false,
(bool) door_open[d] = false, (d = 1 .. number_of_doors)
(position) from = station1,
(position) to = station2,
(position) at = some_position,
(bool) engaging, engaged, leaving, alert;

handle (bool) alert;

derivate
(bool) engaging = running ^ to == at,
(bool) leaving = running ^ from == at,
(bool) engaged = !running;

protocol
engaging ^ !alert -> alert = true; guard(); sm();
leaving ^ alert -> alert = false; delete guard(), sm();

}

The door
agent door((int) d) {

oracle (int) pos[p], door[p]; (p = 1 .. number_of_passengers)

state (bool) queuing[d], occupied[d], around[d];

derivate
queuing[d] = there exists p such that join_queue[p,d] == true;
occupied[d] = there exists p such that (pos[p] == AT_DOOR ^ door[p] == d)
around[d] = there exists p such that (door[p] == d ^
(pos[p] == IN_DOOR || pos[p] == AT_DOOR || pos[p] == OUT_DOOR))

protocol queuing[d] ^ !occupied[d] ^ join_queue[p,d] == true
-> pos[p] = AT_DOOR; (p = 1 .. number_of_passengers)
}