Page 196 - The Unofficial Guide to Lego Mindstorms Robots

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task. However, if you do this, the robot "jiggles" badly. The prob lem is that arbitrate changes the value of
motorCommand several times each tim e it loops. As the value changes, motorControl responds by changing the
motors' directions.

We're really inter ested only in the value of motorCommand at the end of each loop in arbitrate. Therefore,
motorContr ol is implemented as a subroutine and is called once each time at the end of the arbitrate loop.

The RoboTag Program

On ce you get through the details of implementing subsumption architecture, the rest of the programming is pretty simple. The
Ro boTag program uses its main task to start up all the behavior tasks and, of course, arbitrate. It also uses the light
sensor initialization code from M inerva (see Chapter 5, Minerva, a Robot with an Arm) to calculate a baseline value for the
light sensor. When the light sensor reads lower than the average, the RoboTag robot can assume it's reached th e edge of the
arena.

Here is the entire code for RoboTag. You should download this program to both of the robots that will be playing.

// Mot or commands.
#de fin e COMMAND_NONE -1
# de fine COMMAND_FORWARD 1
#define COMMAND_REVERS E 2
#define COMMAND_LEFT 3
#define COMMAND_RIGHT 4
#define COMMAND_STOP 5
#define COMMAND_FLOAT 6

// IR messages.
#define MESSAGE_TAG 33
#define MESSAGE_ACKNOWLEDGE 6

#define BUMP_SENSOR SE NSOR_1
#define LIGHT_SENSOR SENSOR_2

int score;
int averageLight;

int cruiseCommand;

task cruise() {
cruiseCommand = COMMAND_FORWARD;
while (true) Wait( 100);
}

int tagCommand;

task tag() {