Gameboy Development Forum

actually I had done it on an old Yamaha keyboard then transcribed it to 8bit using Audacity, however that's been put out the window. I have coded a tune, the next step for me is working out how to pretty much multithread so that the song plays in the background while your doing other stuff. So for example, how would I press SELECT half way through the song causing the game to stop the song and exit the menu. Here is the code:

    while(looping1 != loops1){
        looping1 = looping1 + 1;
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        //square 1 (NR10-14)
       
        NR10_REG = 0x00;
        NR11_REG = 0x00;
        NR12_REG = 0xAA;
        NR13_REG = 0x00;
        NR14_REG = 0x87;
       
        delay(tempo1);
       
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        NR10_REG = 0x00;
        NR11_REG = 0x10;
        NR12_REG = 0xAA;
        NR13_REG = 0x22;
        NR14_REG = 0x87;

       
        delay(tempo1);
       
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        NR10_REG = 0x00;
        NR11_REG = 0x10;
        NR12_REG = 0xAA;
        NR13_REG = 0x55;
        NR14_REG = 0x87;
       
        delay(tempo1);
       
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        NR10_REG = 0x00;
        NR11_REG = 0x10;
        NR12_REG = 0xAA;
        NR13_REG = 0x33;
        NR14_REG = 0x87;
       
        delay(tempo1);
       
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        NR10_REG = 0x00;
        NR11_REG = 0x10;
        NR12_REG = 0xAA;
        NR13_REG = 0x00;
        NR14_REG = 0x87;

        delay(tempo1);
       
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        NR10_REG = 0x00;
        NR11_REG = 0x10;
        NR12_REG = 0xAA;
        NR13_REG = 0x33;
        NR14_REG = 0x87;
       
        delay(tempo1);
       
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        NR10_REG = 0x00;
        NR11_REG = 0x10;
        NR12_REG = 0xAA;
        NR13_REG = 0x22;
        NR14_REG = 0x87;
       
        delay(tempo1);
       
        NR52_REG = 0x80;
        NR51_REG = 0x11;
        NR50_REG = 0x77;
       
        NR10_REG = 0x00;
        NR11_REG = 0x10;
        NR12_REG = 0xAA;
        NR13_REG = 0x00;
        NR14_REG = 0x87;
       
        delay(tempo1);
       
    }

Last edited by jobalisk (2017-10-04 20:27:59)

To play music, there are two options: Either you use an existing player (like GBTPlayer or Carillon) or you go for the do-it-youself approach. I have no experience with any of the players, so I can't help you with them. But what you're trying to do in your code example is the do-it-youself approach. I'll give you a brief explanation on how that can work and a code example. I'm not saying that it's the only, easiest or smartest way but it's one that works. Proceed as follows:

1. Set up a data array with values that represent the sounds you want to play (MusicData in the example below).

2. Write a function (PlaySound in the example below) that reads one value from your data array, translates it into the respective values for the Game Boy's sound registers and writes the respective values to the sound registers. Make sure that this function only plays one sound at a time depending on the value of a counter variable (SongCounter in the example below). It is not supposed to play the complete song.

3. Write an interrupt service routine that will be triggered by the timer interrupt. Each time the timer interrupt service routine is called, it increases a counter variable (SongInterruptCounter in the example below). If the counter reaches a maximum (SongSpeed in the example below), it resets the SongInterruptCounter to zero, increases the SongCounter by one and calls the PlaySound function. If the SongCounter reaches the end of the song (SongLength in the example), it must also be reset to zero, so the song loops.

4. In your main function you only have to take the following steps:

    a. Initialize the Game Boy's sound unit.

    b. Initialize your variables (SongCounter, SongInterruptCounter, SongSpeed, SongLength).

    c. Set up the timer interrupt.

    d. Enter your main loop. Do, whatever your game needs to do. The music will play in the background.

#include <\gb\gb.h>
#include <stdio.h>

UINT16 SongLength;
UINT8  SongSpeed;
UINT8  SongInterruptCounter;
UINT16 SongCounter;

const UINT8 MusicData[] = {

    // Data array that contains the notes of your song.

};

void PlaySound()
{

    // Read the value at the position of SongCounter from the MusicData array...
    // ...translate it into the respective values for the sound registers...
    // ...and write these values to the registers.
    // Make sure you only play one note at a time.
    // For testing purposes you can ignore the array and always play the same note.

}

void TimerISR()
{

    SongInterruptCounter++;
    
    if (SongInterruptCounter == SongSpeed)
    {
                
        PlaySound();
        SongCounter++;
        if (SongCounter == SongLength) SongCounter = 0;
        SongInterruptCounter = 0;
        
    }
        
}
    
void main()
{

    // Initialize sound unit.
    
    NR52_REG = 0x80;
    NR51_REG = 0xFF;
    NR50_REG = 0x77;
    
    // Dont' forget to initialize the waveform data for channel 3 if you want to use it.
    
    // Initialize variables.
    
    SongInterruptCounter = 0;
    SongCounter          = 0;
    SongSpeed            = 20;  // Higher value results in a slower tempo.
    SongLength           = 327; // Number of notes of your song.
    
    // Set up the timer interrupt.
    
    disable_interrupts();
    add_TIM(TimerISR);
    enable_interrupts();
    TAC_REG = 0x06;
    set_interrupts(TIM_IFLAG);

    // Main loop.
    
    while(!0) {
    
        // Fill in the code for your game here. The music will play in the background.
    
    }
        
}

The above code can be shortened a little if you use a switch statement instead of all those else if statements.
https://www.tutorialspoint.com/cprogram … t_in_c.htm

Last edited by chris (2017-10-07 23:47:35)

jobalisk wrote:

thank you, as you can see by the above post I have worked out a way of doing it myself but this is quite useful. I can't however get more than 1 channel to play at once, not sure why.

I guess the reason is that you change the value of NR51_REG before you play each sound. Try to set NR51_REG only once in the initialization procedure of your game and set it to 0xFF. That will waste a bit of battery life on the real hardware but should enable you to use all channels simultaneously.

Last edited by Jonas (2017-10-08 08:20:05)

8-bit integer notes for chromatic scale from C to B.

C      13,
C#    40,
D      68,
EF     91,
E      114,
F      137,
F#    157,
G      177,
G#    195,
A       214,
BF     231,
B       247