Music is not playing

I want my line follower to play music while it’s following the line. I have the following code:

/*
 * 3pi-linefollower-pid - demo code for the Pololu 3pi Robot
 * 
 * This code will follow a black line on a white background, using a
 * PID-based algorithm.
 *
 * https://www.pololu.com/docs/0J21
 * https://www.pololu.com
 * https://forum.pololu.com
 *
 */

// The 3pi include file must be at the beginning of any program that
// uses the Pololu AVR library and 3pi.
#include <pololu/3pi.h>

// This include file allows data to be stored in program space.  The
// ATmega168 has 16k of program space compared to 1k of RAM, so large
// pieces of static data should be stored in program space.
#include <avr/pgmspace.h>

// Introductory messages.  The "PROGMEM" identifier causes the data to
// go into program space.
const char welcome_line1[] PROGMEM = " Pololu";
const char welcome_line2[] PROGMEM = "3\xf7 Robot";
const char demo_name_line1[] PROGMEM = "PID Line";
const char demo_name_line2[] PROGMEM = "follower";

// A couple of simple tunes, stored in program space.
const char welcome[] PROGMEM = ">g32>>c32";
const char go[] PROGMEM = "L16 cdegreg4";

// Data for generating the characters used in load_custom_characters
// and display_readings.  By reading levels[] starting at various
// offsets, we can generate all of the 7 extra characters needed for a
// bargraph.  This is also stored in program space.
const char levels[] PROGMEM = {
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b00000,
	0b11111,
	0b11111,
	0b11111,
	0b11111,
	0b11111,
	0b11111,
	0b11111
};

// This function loads custom characters into the LCD.  Up to 8
// characters can be loaded; we use them for 7 levels of a bar graph.
void load_custom_characters()
{
	lcd_load_custom_character(levels+0,0); // no offset, e.g. one bar
	lcd_load_custom_character(levels+1,1); // two bars
	lcd_load_custom_character(levels+2,2); // etc...
	lcd_load_custom_character(levels+3,3);
	lcd_load_custom_character(levels+4,4);
	lcd_load_custom_character(levels+5,5);
	lcd_load_custom_character(levels+6,6);
	clear(); // the LCD must be cleared for the characters to take effect
}

// This function displays the sensor readings using a bar graph.
void display_readings(const unsigned int *calibrated_values)
{
	unsigned char i;

	for(i=0;i<5;i++) {
		// Initialize the array of characters that we will use for the
		// graph.  Using the space, an extra copy of the one-bar
		// character, and character 255 (a full black box), we get 10
		// characters in the array.
		const char display_characters[10] = {' ',0,0,1,2,3,4,5,6,255};

		// The variable c will have values from 0 to 9, since
		// calibrated values are in the range of 0 to 1000, and
		// 1000/101 is 9 with integer math.
		char c = display_characters[calibrated_values[i]/101];

		// Display the bar graph character.
		print_character(c);
	}
}

// Initializes the 3pi, displays a welcome message, calibrates, and
// plays the initial music.
void initialize()
{
	unsigned int counter; // used as a simple timer
	unsigned int sensors[5]; // an array to hold sensor values

	// This must be called at the beginning of 3pi code, to set up the
	// sensors.  We use a value of 2000 for the timeout, which
	// corresponds to 2000*0.4 us = 0.8 ms on our 20 MHz processor.
	pololu_3pi_init(2000);
	load_custom_characters(); // load the custom characters
	
	// Play welcome music and display a message
	print_from_program_space(welcome_line1);
	lcd_goto_xy(0,1);
	print_from_program_space(welcome_line2);
	play_from_program_space(welcome);
	delay_ms(1000);

	clear();
	print_from_program_space(demo_name_line1);
	lcd_goto_xy(0,1);
	print_from_program_space(demo_name_line2);
	delay_ms(1000);

	// Display battery voltage and wait for button press
	while(!button_is_pressed(BUTTON_B))
	{
		int bat = read_battery_millivolts();

		clear();
		print_long(bat);
		print("mV");
		lcd_goto_xy(0,1);
		print("Press B");

		delay_ms(100);
	}

	// Always wait for the button to be released so that 3pi doesn't
	// start moving until your hand is away from it.
	wait_for_button_release(BUTTON_B);
	delay_ms(1000);

	// Auto-calibration: turn right and left while calibrating the
	// sensors.
	for(counter=0;counter<80;counter++)
	{
		if(counter < 20 || counter >= 60)
			set_motors(40,-40);
		else
			set_motors(-40,40);

		// This function records a set of sensor readings and keeps
		// track of the minimum and maximum values encountered.  The
		// IR_EMITTERS_ON argument means that the IR LEDs will be
		// turned on during the reading, which is usually what you
		// want.
		calibrate_line_sensors(IR_EMITTERS_ON);

		// Since our counter runs to 80, the total delay will be
		// 80*20 = 1600 ms.
		delay_ms(20);
	}
	set_motors(0,0);

	// Display calibrated values as a bar graph.
	while(!button_is_pressed(BUTTON_B))
	{
		// Read the sensor values and get the position measurement.
		unsigned int position = read_line(sensors,IR_EMITTERS_ON);

		// Display the position measurement, which will go from 0
		// (when the leftmost sensor is over the line) to 4000 (when
		// the rightmost sensor is over the line) on the 3pi, along
		// with a bar graph of the sensor readings.  This allows you
		// to make sure the robot is ready to go.
		clear();
		print_long(position);
		lcd_goto_xy(0,1);
		display_readings(sensors);

		delay_ms(100);
	}
	wait_for_button_release(BUTTON_B);

	clear();

	print("Go!");		

	// Play music and wait for it to finish before we start driving.
	play_from_program_space(go);
	while(is_playing());
}

// This is the main function, where the code starts.  All C programs
// must have a main() function defined somewhere.
int main()
{
	const char fugue[] PROGMEM = 
    "! T120O5L16agafaea dac+adaea fa<aa<bac#a dac#adaea f"
    "O6dcd<b-d<ad<g d<f+d<gd<ad<b- d<dd<ed<f+d<g d<f+d<gd<ad"
    "L8MS<b-d<b-d MLe-<ge-<g MSc<ac<a MLd<fd<f O5MSb-gb-g"
    "ML>c#e>c#e MS afaf ML gc#gc# MS fdfd ML e<b-e<b-"
    "O6L16ragafaea dac#adaea fa<aa<bac#a dac#adaea faeadaca"
    "<b-acadg<b-g egdgcg<b-g <ag<b-gcf<af dfcf<b-f<af"
    "<gf<af<b-e<ge c#e<b-e<ae<ge <fe<ge<ad<fd"
    "O5e>ee>ef>df>d b->c#b->c#a>df>d e>ee>ef>df>d"
    "e>d>c#>db>d>c#b >c#agaegfe fO6dc#dfdc#<b c#4";
	
	play_mode(PLAY_AUTOMATIC);
	
	unsigned int sensors[5]; // an array to hold sensor values
	unsigned int last_proportional=0;
	long integral=0;

	// set up the 3pi
	initialize();

	// This is the "main loop" - it will run forever.
	while(1)
	{
		if(!is_playing()) play_from_program_space(fugue);
		
		// Get the position of the line.  Note that we *must* provide
		// the "sensors" argument to read_line() here, even though we
		// are not interested in the individual sensor readings.
		unsigned int position = read_line_white(sensors,IR_EMITTERS_ON);

		// The "proportional" term should be 0 when we are on the line.
		int proportional = ((int)position) - 2000;

		// Compute the derivative (change) and integral (sum) of the
		// position.
		int derivative = proportional - last_proportional;
		integral += proportional;

		// Remember the last position.
		last_proportional = proportional;

		// Compute the difference between the two motor power settings,
		// m1 - m2.  If this is a positive number the robot will turn
		// to the right.  If it is a negative number, the robot will
		// turn to the left, and the magnitude of the number determines
		// the sharpness of the turn.
		int power_difference = proportional/6 + integral/15000 + derivative*8;

		// Compute the actual motor settings.  We never set either motor
		// to a negative value.
		const int max = 255;
		if(power_difference > max)
			power_difference = max;
		if(power_difference < -max)
			power_difference = -max;

		if(power_difference < 0)
			set_motors(max+power_difference, max);
		else
			set_motors(max, max-power_difference);
			
		if(proportional >= 500)
		{
            green_led(1);
		}
		if(proportional <= -500)
		{
		    red_led(1);
		}	
		else if(proportional >= -499 && proportional <= 499)
		{
			green_led(0);
			red_led(0);
		}				  
	}

	// This part of the code is never reached.  A robot should
	// never reach the end of its program, or unpredictable behavior
	// will result as random code starts getting executed.  If you
	// really want to stop all actions at some point, set your motors
	// to 0,0 and run the following command to loop forever:
	//
	// while(1);
}

// Local Variables: **
// mode: C **
// c-basic-offset: 4 **
// tab-width: 4 **
// indent-tabs-mode: t **
// end: **

It’s a modified version of the sample PID code. It follows the line great, but the music doesn’t get played, and I don’t know why. Please help? :mrgreen:

EDIT: oops, posted the wrong code. fixed.

Hello,

I am sorry that you are having trouble with your code. But if you want to get help, you should simplify your code to the simplest thing possible that demonstrates the problem, and tell us exactly what it does wrong. With a little experimentation, you should be able to give us a 3- or 4-line program that does not work the way it should, and that will make it much easier to see the problem.

Alternatively, if you started with an example project, you could start over and see if you can find out exactly which change causes the problem. If you can tell us that making a single small change causes something to break, it should be easy to figure out.

By the way, did your 3pi play music with an unmodified demo program?
-Paul

Hmm. I figured it out. The problem was that I didn’t make the melody a global variable. It was local to the main task. Thanks anyway.