Final Exam — sunnypilot Architecture Tour

1. [Module 0] In the pub/sub pattern sunnypilot's processes use, what does a publisher need to know about its subscribers?

Their process IDs, so it can send directly to each one Nothing — it publishes without knowing or caring who is listening How many there are, so it can fan out the right number of copies Their subscription start time, to replay any missed messages

2. [Module 0] What is msgq?

The typed schema language that defines message fields The shared-memory transport that cereal's pub/sub API runs on The on-disk log format used for recorded drives comma's cloud service for uploading drives

3. [Module 1] What actually decides whether a given enabled process should be running right now?

manager.py contains an if-statement per process It's decided once at boot and doesn't change while the device is on That process's own condition function, re-evaluated every manager loop iteration The process decides for itself and reports back to manager.py

4. [Module 1] True or false: if a process has enabled=False on this hardware, its condition function still gets called every loop to double-check.

True False

5. [Module 1] Which environment variable, read once in manager_thread, lets you name specific processes to hold back regardless of their own condition function?

6. [Module 2] In SubMaster, when is sm.updated['carState'] True?

On every sm.update() call, as long as carState has ever arrived once Only on the update() call where a fresh carState message just arrived Only after sm.valid['carState'] becomes True for the first time Only if no other subscriber has already read that message

7. [Module 2] True or false: two separate processes can both subscribe to carState at the same time and both see every message.

True False

8. [Module 2] When you run tools/replay/replay --demo, what is actually producing the modelV2 messages you subscribe to?

The exact bytes modeld wrote during the original recorded drive, replayed at their original timing A live instance of modeld, re-run against the replayed camera frames A synthetic message generated by the replay tool itself comma's cloud servers, streamed live during playback

9. [Module 3] When longitudinalPlan.longitudinalPlanSource reads e2e, what does aTarget actually contain?

A direct copy of modelV2.action.desiredAcceleration, unconditionally The smaller of the model's suggestion and a separately-computed classical MPC solution The classical MPC solver's output, with the model ignored An average of the model's and the MPC's suggestions

10. [Module 3] Which process publishes radarState?

11. [Module 3] Which field tells you whether a lead car is currently being tracked at all?

longitudinalPlan.hasLead radarState.leadOne.status carControl.cruiseControl.override modelV2.leadsV3[0].prob only

12. [Module 4] Which cereal field would you subscribe to for sunnypilot's steering-only MADS paused state?

selfdriveState.state selfdriveStateSP.mads.state carControl.latActive onroadEvents

13. [Module 4] True or false: the engage/disengage state machine can go directly from disabled to overriding on the same cycle, without ever publishing plain enabled in between.

True False

14. [Module 4] What causes a transition from overriding back to enabled?

A fixed timer expiring, regardless of driver input The driver pressing the cruise-main button again Neither OVERRIDE_LATERAL nor OVERRIDE_LONGITUDINAL being present anymore softDisabling's timer reaching zero

15. [Module 5] panda's torque rate-limit check constrains a newly commanded value against which reference?

Whatever value controlsd itself commanded last time, as controlsd reports it The car's own measured torque or the driver's applied torque, read directly off CAN A machine-learned prediction of the correct torque The previous cycle's plannerd output only

16. [Module 5] True or false: panda's safety firmware recomputes what it believes the correct steering torque should be, independent of what controlsd requests.

True False

17. [Module 5] What does mads_heartbeat_engaged_check do after three consecutive mismatches between panda's controls_allowed_lateral and the Linux-side heartbeat?

Nothing; it only logs the mismatch for later diagnostics It requests a full device reboot It forcibly disengages lateral control itself It raises the torque limit as a safety margin

18. [Module 1] Why do some imports in this codebase start with openpilot. while process_config.py's own process entries use bare names like selfdrive.controls.controlsd?

They're two unrelated copies of the same code that must be kept in sync manually An `openpilot/` directory of symlinks makes both names resolve to the exact same file The bare form only works during tests, never at runtime `openpilot.` is deprecated and being phased out

19. [Module 2] What does tools/replay/replay --demo require that a real car or comma account would otherwise provide?

A comma account and a registered dongle ID Nothing — it fetches a fixed, published public route with no account or hardware A connected panda board, for safety-model validation A local GPU, to re-run the driving model live