Integration planning

Example 1 Ordering tasks and finding the critical path

tasks = {   # task: (hours, predecessors)
    "power distribution": (3, []),
    "flight controller": (2, ["power distribution"]),
    "RC receiver": (1, ["flight controller"]),
    "GNSS + compass": (2, ["flight controller"]),
    "telemetry radio": (1, ["flight controller"]),
    "ESCs + motors": (3, ["power distribution", "flight controller"]),
    "companion computer": (3, ["power distribution", "flight controller"]),
    "camera trigger": (2, ["companion computer", "flight controller"]),
}

indeg = {t: len(p) for t, (_, p) in tasks.items()}
order, ready = [], [t for t, d in indeg.items() if d == 0]
while ready:
    t = ready.pop(0)
    order.append(t)
    for u, (_, pred) in tasks.items():
        if t in pred:
            indeg[u] -= 1
            if indeg[u] == 0:
                ready.append(u)
assert len(order) == len(tasks), "dependency cycle"

finish, prev = {}, {}
for t in order:
    d, pred = tasks[t]
    start = max((finish[p] for p in pred), default=0)
    prev[t] = max(pred, key=lambda p: finish[p]) if pred else None
    finish[t] = start + d
end = max(finish, key=finish.get)
path, t = [], end
while t:
    path.append(t)
    t = prev[t]
print("order:", " -> ".join(order))
print(f"total effort {sum(d for d, _ in tasks.values())} h, earliest finish with parallel work {finish[end]} h")
print("critical path:", " -> ".join(reversed(path)))

order: power distribution -> flight controller -> RC receiver -> GNSS + compass -> telemetry radio -> ESCs + motors -> companion computer -> camera trigger
total effort 17 h, earliest finish with parallel work 10 h
critical path: power distribution -> flight controller -> companion computer -> camera trigger

One person needs the full total effort, but with two or three people the tasks on the critical path are the ones to watch; the others can slip without delaying the whole job. The program also reports immediately if the graph contains a cycle, which means the written order contradicts itself.

Example 2 Checking port and I2C allocation

PORTS = {"SERIAL1": {"name": "TELEM1", "flow": True}, "SERIAL2": {"name": "TELEM2", "flow": True},
         "SERIAL3": {"name": "GPS1", "flow": False}, "SERIAL5": {"name": "TELEM3", "flow": True}}
PROTO = {2: "MAVLink2", 5: "GPS"}
plan = [   # device, port, SERIALn_PROTOCOL, SERIALn_BAUD, needs flow control
    ("telemetry radio", "SERIAL1", 2, 57, False),
    ("companion computer", "SERIAL3", 2, 921, True),
    ("GNSS", "SERIAL3", 5, 115, False),
    ("ground display radio", "SERIAL5", 2, 57, False),
]
i2c = {"external bus": [("GNSS module compass", 0x0E), ("add-on compass", 0x0E), ("barometer", 0x77)]}

used, issues = {}, []
for dev, port, proto, baud, need_flow in plan:
    if port in used:
        issues.append(f"{port} used by both {used[port]} and {dev}")
    used[port] = dev
    if need_flow and not PORTS[port]["flow"]:
        issues.append(f"{dev} needs flow control but {port} ({PORTS[port]['name']}) has none")
    print(f"{port:<8}{PORTS[port]['name']:<7} {dev:<21} {PROTO[proto]:<9} baud code {baud}")
for bus, devs in i2c.items():
    seen = {}
    for dev, addr in devs:
        if addr in seen:
            issues.append(f"I2C {bus}: {dev} and {seen[addr]} both at 0x{addr:02X}")
        seen[addr] = dev
print("issues:", *issues, sep="\n  ")
free = [p for p in PORTS if p not in used]
print("free ports:", free)

SERIAL1 TELEM1  telemetry radio       MAVLink2  baud code 57
SERIAL3 GPS1    companion computer    MAVLink2  baud code 921
SERIAL3 GPS1    GNSS                  GPS       baud code 115
SERIAL5 TELEM3  ground display radio  MAVLink2  baud code 57
issues:
  companion computer needs flow control but SERIAL3 (GPS1) has none
  SERIAL3 used by both companion computer and GNSS
  I2C external bus: add-on compass and GNSS module compass both at 0x0E
free ports: ['SERIAL2']

This plan has three problems that really do happen: the companion computer is on the GPS port, which clashes with the GNSS and has no flow control, and two compasses of the same model sit on one bus. The fix is to move the companion computer to SERIAL2, which is free and has flow control, and to choose an add-on compass whose address can be changed, or put it on another bus.