Simple sound effect sample GameBoy GBDK

main.c

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

void main(){
    // these registers must be in this specific order!
    NR52_REG = 0x80; // is 1000 0000 in binary and turns on sound
    NR50_REG = 0x77; // sets the volume for both left and right channel just set to max 0x77
    NR51_REG = 0xFF; // is 1111 1111 in binary, select which chanels we want to use in this case all of them. One bit for the L one bit for the R of all four channels


    while(1) {
        UBYTE joypad_state = joypad();
        
        if(joypad_state) {   
            // see https://github.com/bwhitman/pushpin/blob/master/src/gbsound.txt
            // chanel 1 register 0, Frequency sweep settings
            // 7	Unused
            // 6-4	Sweep time(update rate) (if 0, sweeping is off)
            // 3	Sweep Direction (1: decrease, 0: increase)
            // 2-0	Sweep RtShift amount (if 0, sweeping is off)
            // 0001 0110 is 0x16, sweet time 1, sweep direction increase, shift ammount per step 110 (6 decimal)
            NR10_REG = 0x16; 

            // chanel 1 register 1: Wave pattern duty and sound length
            // Channels 1 2 and 4
            // 7-6	Wave pattern duty cycle 0-3 (12.5%, 25%, 50%, 75%), duty cycle is how long a quadrangular  wave is "on" vs "of" so 50% (2) is both equal.
            // 5-0 sound length (higher the number shorter the sound)
            // 01000000 is 0x40, duty cycle 1 (25%), wave length 0 (long)
            NR11_REG = 0x40;

            // chanel 1 register 2: Volume Envelope (Makes the volume get louder or quieter each "tick")
            // On Channels 1 2 and 4
            // 7-4	(Initial) Channel Volume
            // 3	Volume sweep direction (0: down; 1: up)
            // 2-0	Length of each step in sweep (if 0, sweeping is off)
            // NOTE: each step is n/64 seconds long, where n is 1-7	
            // 0111 0011 is 0x73, volume 7, sweep down, step length 3
            NR12_REG = 0x73;  

            // chanel 1 register 3: Frequency LSbs (Least Significant bits) and noise options
            // for Channels 1 2 and 3
            // 7-0	8 Least Significant bits of frequency (3 Most Significant Bits are set in register 4)
            NR13_REG = 0x00;   

            // chanel 1 register 4: Playback and frequency MSbs
            // Channels 1 2 3 and 4
            // 7	Initialize (trigger channel start, AKA channel INIT) (Write only)
            // 6	Consecutive select/length counter enable (Read/Write). When "0", regardless of the length of data on the NR11 register, sound can be produced consecutively.  When "1", sound is generated during the time period set by the length data contained in register NR11.  After the sound is ouput, the Sound 1 ON flag, at bit 0 of register NR52 is reset.
            // 5-3	Unused
            // 2-0	3 Most Significant bits of frequency
            // 1100 0011 is 0xC3, initialize, no consecutive, frequency = MSB + LSB = 011 0000 0000 = 0x300
            NR14_REG = 0xC3;	    

            delay(1000);
        }
    }
}