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日期:2020-09-19 10:10

1 | ANU College of Engineering and Computer Science September 2020
Gliding in Space
Assignment for all students of Systems, Networks and Concurrency 2020
This is a carefully evaluated and marked assignment. Thus extra care is expected on all levels.
Overview
Coordinating behaviours and resources in a concurrent and distributed way is at the heart of
this course. The background this year is a swarm of physical vehicles in 3-d space.
The code framework which will model and simulate a swarm of vehicles showing default behaviours
which keep them in motion, together as well as collision-free is provided to you. All vehicles
have a local “charge” to keep them “alive”. For physical reasons yet unknown, the vehicles
replenish their charge to full by passing “energy globes” in close proximity. Vehicles which run
out of charge mysteriously disappear. Vehicles constantly consume a little bit of energy to keep
their on-board systems running, and consume more substantial amounts of energy when accelerating
or decelerating.
Sensors, Actuators &
Communication
Each vehicles is operated by a dedicated
task which has access to local sensors, communication
interfaces and actuators.
The sensors include position, velocity and
acceleration as well as current charge. If the
vehicle is close enough to one or multiple energy
globes to utilize them, the sensors also
display the position and current velocity of all close energy globes.
The actuator system consists of setting an absolute destination position and throttle value. The
underlying cruise control systems automatically handles the steering and acceleration. Once
the destination point has been reached the throttle automatically switches back to idle which
means that default swarming behaviour takes over. The vehicles do not slow down when approaching
the destination point and rather pass through the destination point. This helps to
keep the controls fluent and the vehicles in motion. Collision avoidance reflexes are always active
and prevent vehicles from crashing into each other. Note that destinations might become
unreachable, if multiple vehicles are bound for the same destination.
The vehicles are also equipped with a message passing system which allows to broadcast a
message which will be received by all vehicles in close proximity. This is asynchronous and
there is no feedback whether any message has been received by any vehicle – unless another
vehicle actively sends a message in response of course.
Finally there is also a function which allows direct access to the underlying, secret clock of the
world. Wait_For_Next_Physics_Update will put the task to sleep until anything actually happened
(which includes communication). This relieves the vehicles from busy waiting on the
world to change.
All the above controls are found in Sources/Vehicle_Interface/vehicle_interface.ads.
2 | ANU College of Engineering and Computer Science September 2020
The Animation
The provided graphical animation of the swarm offers third person views as well as the view
from one of the vehicles while it is passing through the swarm. The communication range can
be visualized by drawing connecting lines between all vehicles which are currently in communication
range. The colours represent their charging state as well as the control state. Turquoise
vehicles are currently following their swarming instincts are not explicitly controlled by the associated
task. The colour saturation reflects the level of charge. Once vehicles go into manual
control (throttle and destination is set) they turn to a more red colour schema. The energy
globe(s) are dark ruby coloured spheres.
Design Constraints
The final solution which is requested from you should be deployable on actual vehicles. Hence
only the provided interfaces to physical sensors and forms of communications are allowed.
“Looking underneath the hood” is still encouraged of course if you want to see how such a
simulation can be implemented on a computer system. Bypassing the provided interfaces and
using information from inside the simulator is obviously counterproductive for any future physical
deployment and hence not allowed. Nevertheless the first stage of the assignment will allow
you to introduce additional means of communication which can not necessarily be physically
implemented.
Timing Constraints
All calculations inside the vehicle tasks have an implicit deadline given by the update from the
underlying physics engine. This deadline is not hard as seen by the local tasks, yet many tasks
overrunning this deadline concurrently will slow down the simulator. Simulated time is not affected
by this – only the update time intervals will become larger.
Design Goals
The overall design goal is to keep as many vehicles alive as possible for as long as possible. As
energy globes can only be discovered locally, communication is required, as well as coordination
between the vehicles as all swarm members heading for the some destination at the same
time will not lead to many of them making it there.
3 | ANU College of Engineering and Computer Science September 2020
The task can be solved in four stages:
a. Allowing a central coordinator.
b. Fully distributed.
c. Multiple energy globes.
d. Find harmony.
Stage a still allows for a central coordinator
to be introduced and all tasks
are allowed to communicate with
this entity (or multiple thereof). The
implementation of those central instances
can employ shared memory
based as well as message based forms of communication. Some are obviously questionable to
impossible in a physical deployment of your system, yet this stage might help you to develop
ideas which can then be considered for the second stage.
Stage b does not allow for a central coordinator and all planning and scheduling now needs
to be done on the individual vehicles only using local communication. This is hard. If you are
confident that you are up for stage b straight out then you do not need to implement stage a.
Stage c requires further coordination between vehicles as multiple energy globes are to be
considered. Assume that you do not know how many globes are in existence, yet utilize the
additional redundancy which is detected at runtime to enhance the overall robustness of your
swarm charging method. To test this you will need to go to the package Swarm_Configuration
and change Configuration to Random_Globes_In_Orbits. Globes can appear and vanish at
random, yet there will be a minimum of 2 globes around at all times.
Stage d requires all of the above plus that the swarm shrinks itself to a specific size. This size
is a constant (Target_No_of_Elements) which is known to all vehicles, yet they do not know
(initially) how many vehicles there are in total, or whether they themselves are scheduled for
destruction. This stage will require a fully distributed method to share information and agree on
action (in this case, to purposefully let certain vehicles run out of energy and vanish).
Criteria
The first criterion is to get over the initial phase without anybody dying. This can be a impossible,
if still nobody found an energy globe before the initial charges run out. Don’t worry about
this case – this is just nature and you cannot do anything about it.
Yet once one or multiple globes are found you need to make sure that the information is spread
effectively.
Now comes the real challenge of how to coordinate the vehicles. Find ways to coordinate their
paths. This might be leading to different strategies in stage a and stage b.
The Programming Framework
The provided code has been successfully compiled and tested on the lab computers and:
? Linux: Ubuntu version 10, 14.04, and lab computers. Depending on the Linux version, it
might be necessary to install glutg3 and glutg3-dev (via a package manager, if you are lucky).
? Mac OS: PowerPC and Intel (32 and 64bit), tested on 10.5 to 10.15.
? Windows: tested on XP, Vista, Win7 and Win10. The freeglut library needs to be in the same
directory as the executable (already placed to the right spot in the provided project).
Please note the different project files which refer to different operating systems and select the
one fitting your computer when opening the project.
Parts of the provided framework are based on the Globe_3D project (an OpenGL 3D engine),
which is maintained by Gautier de Montmollin.
4 | ANU College of Engineering and Computer Science September 2020
Deliverables
You need to submit a report (in pdf) as well as your code (only the source files inside the directory
Student_Packages - please do not submit the whole framework or your binary files). The
report is your chance to convince us that your concept is great – even though your code might
not have run according to expectations. Conversely, even though your code might be a strike
of genius, we might not have recognized it without your great report along with it.
Report
? Documentation of your design. Specific emphasis should be given to explain your design
decisions. Give reasons for each of those. Make clear which constraints you employed
as ‘driving concepts’, which have been considered, and which have been purposefully
ignored (for instance to allow for a cleaner, easier maintainable design).
? Provide documentation of your test runs. Give a precise motivation for each of your tests.
The following questions might help you to evaluate and describe your design:
? How does your design scale?
? Do you provide for graceful degradation in case that parts of your system become
unresponsive (a mysterious vehicle disappearance case)?
? Do you consider your design dependable and maintainable and why (or why not)?
If you require help in technical/scientific writing, please do not be too shy to ask for it.
Code
Submit only the manipulated packages (vehicle task & message structure) together with the
packages which you added on top. Your code will evaluated according to common professional
practice. We do not enforce a specific coding schema, but request consistency and a general
high standard on the basic coding level. Make sure all your identifiers have good names, all
scopes and access constraints are set as tight as possibly, and full use has been made of
compile time checks. All your code will be read. We do not have the capacity to provide detailed
comments on all code, but will refine the provided feedback on individual request in the
limits of our time.
General
Use graphical or any other means to express your ideas as precisely as you can. Overall assignment
time is four weeks (which includes two weeks of semester break), so we expect a work of
precision and care. Exact due date and submission procedures will be announced on the website
and forums.
Guidelines for the marking are:
? (30%) Functionality of your program - does it implement stage a, b, c or d?
? (30%) Elegance and strictness of your design.
? (30%) Clarity of the report.
? (10%) Provided documentation about test runs.
Expect to be limited to a credit (CR) range marks if your design only considers stage a solutions
and to find yourself in high-distinction (HD) range if your design is a convincing and compete
submission for stage d. Allow yourself plenty of time to come up with a solid concept first.
Without a clear idea you are bound for chaos in this assignment.
This is only a guide. We will feel free to give you more marks if your code is outstanding or your
report is an outstanding example of technical writing.

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