General Avionics Software Specification

1. Paper by: C. Douglass Locke, David R. Vogel, Lee Lucas, John B. Goodenough Presented by: Jeremy Erickson August 27, 2010 General Avionics Software Specification

2. System Structure - Overview Main focus of paper

3. Head-Up Display • The Head-Up Display (HUD) is imposed on the pilot's view out the cockpit. • “Reticles” are crosshairs for potential targets Image source: Wikipedia

4. Multi-Purpose Display (MPD) • Shows anything else needed • Normally a map of tactical situation, but has other modes as well.

5. Keyset • This is just the set of keys the aircrew uses to interact with the computer for things like target selection.

6. Hands-On Throttle and Stick • These are actual hardware controls used to maneuver the plane, which could function even if the mission computer fails.

7. Stores • Stores are “items fastened to racks underneath the aircraft” • In practice, stores we care about are weapons such as bombs. • We have to keep track of how many are left.

8. Display Processor • This processor does low-level stuff to interact with various display hardware. • It's not the focus of this paper, so we don't really know what its tasks look like.

9. Inertial Navigation System • Sensor system that provides information about position and velocity • Also provides reference data for attitude and heading • May have RT tasks, but they're not talked about in this paper.

10. Air Data Computer (ADC) • Barometric altimeter and dynamic and static pressure data • Again, outside the scope of this paper

11. Stores Management System (SMS) • This computer does all the low-level interaction with the weapons and senses the status. • Once again out of scope of the paper

12. Mission Control Computer (MCC) • Main focus of paper that does “navigation, sensor control, weapons targeting and release, controls and displays management, and fault isolation test.” • More on this later...

13. Radar • The main radar component is used to track targets the plane may attack.

14. Radar Altimeter (RALT) • The radar altimeter indicates height above the ground

15. Radar Warning Receiver (RWR) • This component warns when we are scanned by an enemy radar

16. Communication • All systems communicate over a single serial bus. • Communication with the MCC is done entirely using polling, not interrupts. • Interrupts may exist within the MCC, however.

17. Timing • All tasks are executed periodically. • Aperiodic work can happen, but is executed by a periodic task (we would call this a server or a container). • Some tasks may not always run. • The plane will have different modes of operation based on what it is doing (e.g. takeoff vs. combat), but the paper only considers one mode. • Where do timing requirements come from?

18. Three Types of Timing Requirements • Hardware requirements • e.g. communication with sensors • Algorithmic requirements • e.g. numerical stability for weapon delivery computations • Human factors • e.g. making display updates appear “instantaneous”

19. Specific Tasks • Next the paper gets into a “deep dive” with specific tasks in the MCC. • We don't have time to discuss all the details, but we'll discuss the basic categories of tasks.

20. Navigation • These tasks update aircraft position and motion information based on sensors or aircrew input, and provide steering cues to the aircrew. • This category has two periodic tasks which always run.

21. Radar Control • Radar can can operate in ground map, ground search, or single-target track modes, and radar control behaves appropriately. Different tasks are operative in each mode, and the paper ignores ground map mode since it's not used during attack. • A periodic task for each of tracking and searching, and a user-triggered task for initiating tracking.

22. Targeting • Targeting must be done in several stages: A target must be designated and then confirmed. Later, the target must be tracked and in some cases “sweetened” (improved). • Several tasks take care of these functions. Only tracking is periodic; the others are triggered by the user or by previous task completion.

23. Weapon Control • Weapon control involves several stages. • The aircrew selects which weapon(s) to fire, how many, and at what intervals. These are implemented with user-trigggered tasks. • Weapon trajectory is computed with a periodic task but can be reinitiated with an aperiodic task (not sure on trigger). • The weapons are released by a set of scheduled tasks that could be periodic with varying periods

24. Controls and Displays • Both the HUD and the MPD displays need to be updated. The relevant tasks are typically periodic. • Various components must accept user input. These are generally user-trigged tasks.

25. RWR Control • The Radar Warning Receiver must be programmed with specific frequencies it is supposed to care about. • I'm not clear why the task to accept input would be periodic – I'm suspecting a typo in the page 29 table. • I believe both tasks are user-triggered, with the RWR programming done once the input has been processed by the input task.

26. RWR Threat Response • The MCC must poll the RWR to determine if there are any relevant threats. This is done with a periodic task. • When there is a threat, a one-shot job does the actual response, which is just updating the display.

27. Built-In-Test (BIT) • The Built-In-Test is the functionality of testing the hardware components. • One task periodically performs standard tests. • When a failure happens, a warning must be produced. • The “Initiated BIT” test is when the operator requests a specific, non-standard test.

28. Utilization Exceeds 1 • The total utilization of the system exceeds 1, so the system is not schedulable! • However, there are two reasons this isn't actually a problem: • It isn't actually possible for all the tasks to run at once. • Priorities are given which specify what work can be shed if the utilization ever does exceed 1.