______                     
                 /      |       ________     
                /       |____  /        \    
               /        |    \/   _      \   
               \       ___       /_\      \  
                \      \_/          .      \ 
                 \          /\_____/       / 
                  \________/      |       /  
                                  |______/   

Lullaby_in.c Part 1

Sooooo… 0xA is still alive I guess… :)

I’m currently working on a small GBA ROM for an upcoming net release compilation that has the lullaby for theme. The idea is to make a small software that will create lullaby-esque sequences using the 4 legacy DMG sound channels of the GBA. That’s a good excuse to get into DevkitARM, although now I’m thinking that it might have been good to learn GBDK to make a GB ROM instead. Ah well, can’t be bothered to restart and maybe I can use the opportunity to add some graphics.

So far the software is tuned for the Hungarian scale in C, which makes a very dramatic lullaby somehow, I’ll tune later on. It was quite straightforward, the most delicate part being the sound registers, but thanks to belogic everything is super well documented. In a nutshell, it’s all about bitmasking and feeding the right registers with 16bit words.

For instance a simple way to control the noise channel can be made like this:

int setSnd4(int cd, int sta, int stp, int ti, int re)
{
    // DMG Channel 4 Noise parameters, reset and loop control
    // See specs: http://belogic.com/gba/registers.shtml#REG_SOUND4CNT_H
    //
    // cd    -- Clock divider frequency (0-7)
    // sta   -- Counter stages (0-1), 15 or 7
    // stp   -- Counter Pre-Stepper frequency (0-15)
    // ti    -- Timed mode (0-1), continuous or timed
    // re    -- Sound reset

    return (re << 15) | (ti << 14) | (stp << 4) | (sta << 3) | cd;
}

int playNote4(int noise)
{  
    REG_SOUND4CNT_L=0xA100;
    REG_SOUND4CNT_H=noise;

    return 0;
}

playNote4(setSnd4(2,1,10,0,1));

That’s just basic copypasta to get the idea. Once it is sequenced and populated with random values, it sounds like this:

Note: this is recorded from an emulator, too lazy to flash it. Yawn. Sleep. Bye.