radar-task

Repository for University project of the Real-Time Embedded Systems course.
The software is intended to simulate the working of a naval radar, by using randomly moving balls on a flat space. The user can pass a number between 2 and 5 as input parameter, which serves the purpose to dictate the number of samples that the radar has to take before starting to predict the next position of the balls.

Requirements and Installation

The program uses ptask, a Period Real-Time Task interface to pthreads and the Allegro4.4 graphics library.
To install the allegro4.4 library type:

sudo apt-get install liballegro4.4 liballegro4.4-dev on Debian-based systems
sudo yum install allegro allegro‐devel under Red Hat

Build

Go in the program folder and type:

make clean to clean the installation folder
make to build the program

Run

To run the program you must have superuser privileges. You can launch the program using sudo ./radar. Press the i key followed by a number between 2 and 5 and the Enter key to select the number of positions that the radar needs to record before starting to predict the next positions of the balls. Press the Space key to launch balls on the screen and press the ESC key to close the application.

Program Structure

Global Data Structures

The program makes use of global variables and data structures. In particular:

• the status struct type is used to store the information of a single ball (velocity, acceleration, color, ecc...)
• the single m struct is used to store the interceptions made by the radar; it also contains the condition variable ptrt, which is used to synchronize the radar task with the radar tracking task
• the t struct contains the positions computed by the tracking threads

Tasks

The program makes use of the ptask library to create period tasks. In particular, in this program there are three types of periodic tasks:

• radartask is the task used to handle the radar rotation and to intercept the position of the balls when they enter the radar beam
• path_randomizer is a lower priority task that changes the acceleration of the balls at periodic intervals; the balls can either increase their longitudinal acceleration, decrease their longitudinal acceleration or change their transversal acceleration (to simulate a plane turn)
• ball_task is created when the space key is pressed and its purpose is to handle the movement of a single ball, by periodically updating the information stored in the status struct and drawing the ball on the underlying screenbuffer (the balls are shown on the screen only when they are intercepted by the radar beam)

The program also uses conventional posix threads named tracking_thread. Each tracking_thread is assigned to a ball when its position is intercepted by radartaskand it waits to be awakened by the same task when one of these conditions is met:

• case 1: an object is intercepted inside the 'burst' period in which the radar beam intercepts multiple position of the same ball that are then averaged to a single one when the burst is over
• case 2: the burst period is over; the thread is awakened so it can start to compute the mean position of the ball
• case 3: when contact with the ball is lost; the thread then becomes available to track a new ball

To predict the next position of the ball the tracking thread uses only the speed of the ball calculated at the last position if the number of samples given as input(k_samples) is equal to 2. If 3 or more samples are given as input the program can then use the last sample to calculate the acceleration of the ball using the following formula:

given the 4 positions: x3 x2 x1 x0 where x3 is the position to predict, v is the speed and a is the acceleration:

x3 = x2 + (v2 + a*dt)*dt but if v2 = (x2 - x1)/dt and a = (v2 - v1)/dt v1 = (x1 - x0)/dt
x3 = x2 + (2v2 - v1)*dt = x2 + 2(x2 - x1) - (x1 - x0) = 3x2 - 3x1 + x0