Writing exercises¶

An exercise has three parts: its text, its checks and its reference solutions.

1. The text¶

plcyard/data/labs/en/NN-short-name.md, a Markdown file with a header:

---
title: Garage door with a safety photo-eye
simulation: garage
level: 3
symbols:
- %I0.0 Open (PB)
- %I0.2 Stop (NC, PB)
---
# 15. Garage door with a safety photo-eye

**Goal:** …

## Inputs and outputs (Garage door simulation)
| Address | Device |
…

## Requirements
1. …

• simulation is a key of the simulation reference.
• level is 1 to 3.
• symbols name the inputs and wire the switches: (NC) makes a normally closed switch, (PB) a pushbutton that springs back.
• Write the requirements as a numbered list. Each one becomes one check.

2. The checks¶

In plcyard/grader.py, a function per exercise, registered in CHECKS under its number:

def _15(new, out):
    r = new()                       # a fresh PLC running the program, wired to the simulation
    r.ms(100)
    r.sim.open_pressed = True       # act on the machine
    r.ms(100)
    r.sim.open_pressed = False
    r.ms(12000)
    opened = r.sim.position >= 100.0
    out("Open runs the door up and stops at the open limit", opened, f"door at {r.sim.position:.0f} %")

r.ms(n) runs n milliseconds of scans (faster than real time). out(requirement, passed, reason) reports one line; the reason is shown when it fails. Make each check fail for an empty program.

3. The solutions¶

plcyard/data/labs/solutions/NN-short-name.plcy (ladder), .st.plcy and .fbd.plcy. The tests grade all three and expect every check to pass; Compare languages shows them.

Run the tests (see Contributing).