What you learn today
- Two doors, one chamber
- Dangers during the change
- State instead of sequence
Mars morning, the drill outside reports a full ore box. Only a wall lies between you and the outside air. A simple door in it would let base air out every time it opens – and if someone leaves it open, you lose the whole base. That is why you go through an airlock.
Two doors, one chamber
| Part | Job |
|---|---|
| Inner door | separates the base from the chamber |
| Chamber | small room with a gas sensor and an active vent |
| Outer door | separates the chamber from the outside |
Instead of the whole base, only the small chamber changes its pressure. The active vent sucks the chamber air through a pipe into a tank (Vent.Inward, 1) and blows it back in when you come home (Vent.Outward, 0). That way hardly any air is lost.
A trip outside has three steps: inner door shut, pump the chamber empty, outer door open. Coming in is the mirror image: outer door shut, fill the chamber, inner door open.
Dangers during the change
- Both doors open: the base is connected straight to the outside air and vents.
- Opening a door against pressure: if the outer door opens with a full chamber, the chamber air is lost. If the inner door opens with an empty chamber, base air rushes into the chamber and the base pressure drops.
- Vent running with a door open: if it keeps sucking while the outer door is open, it pulls outside air into your air tank.
- Sensor gone: without a reading the chip does not know what is in the chamber. Then no door may open.
State instead of sequence
The first idea is often a sequence with waiting times:
# not like this: sequence with waits
sbn DOOR HASH("Innentuer") Open 0
sleep 5
sbn VENT HASH("Schleuse") On 1
sleep 30
sbn DOOR HASH("Aussentuer") Open 1sleep 30 counts seconds, not kilopascals. If the vent has no power or the tank is full, the chamber is still full after 30 seconds – and the outer door opens anyway. During sleep the chip also reacts to nothing: no sensor failure, no abort.
Better: every tick the chip asks what the situation is right now and derives from it how each device must be set. The lever “Richtung” says where you are going (1 = out), the sensor how full the chamber is:
lbn out LEVER HASH("Richtung") Setting Average
lbn press SENSOR HASH("Schleuse") Pressure Average
slt empty press EMPTY # 1 = chamber empty
and tmp out empty # out AND empty?
sbn DOOR HASH("Aussentuer") Open tmpIf the vent is not running, empty stays 0 and the door stays shut. If the sensor fails, press is NaN, slt returns 0 – and again the door stays shut.
A door can open without your chip wanting it: by hand with a crowbar or through a second chip. Never rely on a door being shut just because you wrote Open 0. When it matters, read Open back.
Diagram
Exercise
Task
For now the airlock is operated by hand; your chip only keeps watch. The doors are named “Innentuer” and “Aussentuer”, plus there is an LED display “Status” and a flashing light “Warnlicht”.
- “Status” shows the state of the doors: inner door open counts 1, outer door open counts 2. Both shut = 0, both open = 3.
- The flashing light is on while both doors are open.
- If a door is missing from the network (NaN), “Status” shows −1 and the flashing light is on.
Hints
Hint 1
State: mul state outer 2, then add state state inner.
Hint 2
Danger: seq danger state 3.
Hint 3
If a door is missing, state is NaN. snan missing state notices it, select then sets −1, and or danger danger missing switches the light on.
Quiz
5 questions. You pass from 60 % – the server does the grading.
Complete the day
- Passed the simulator exercise
- Passed the quiz with at least 60 %
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