SN76489 Sample playing

#include <string.h>

#include "SDL.h"
#include "sms.h"
#include "sound.h"
#include "sn76489.h"
#include "freq.h"
#include "gaw.sn76489.h"

static const int NTSC_LINES_PER_FRAME = 262;
static const int PSG_DIVISOR = 16;
static const int NTSC_FPS = 60;
static const float NTSC_Z80_CLOCK = 3579545.0f;
static const float NTSC_CLOCKS_PER_SAMPLE = 5.073051303855f;

int sms_psg_enabled = 1, sms_ym2413_enabled = 0;

// 60 fps
int delay = 30;
sn76489_t psg;
uint32 psg_samples[313];

Uint32 emu_delay() {
    static Uint32 nextTime = 0;
    Uint32 now = SDL_GetTicks();

    if(nextTime <= now) {
        nextTime = now + delay;
        return 0;
    }

    return(nextTime - now);
}

int main(int argc, char *argv[]) {
    int i;
    float tmp = NTSC_Z80_CLOCK / PSG_DIVISOR / NTSC_FPS / NTSC_LINES_PER_FRAME /
    NTSC_CLOCKS_PER_SAMPLE;
    SDL_Event event;

    if(SDL_Init(SDL_INIT_VIDEO) < 0) {
        return 0;
    }
    atexit(SDL_Quit);

    SDL_Window *window = SDL_CreateWindow("sms-synth", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 320, 200, 0);

    if(window == 0) {
        return 0;
    }

    /* from sms_init */
    for(i = 0; i < NTSC_LINES_PER_FRAME; ++i) {
        psg_samples[i] = (uint32) (tmp * (i + 1)) - (uint32) (tmp * i);
    }

    /* We end up generating 734 samples per frame @ 44100 Hz, 60fps, but we
     need 735. */
    psg_samples[261] += 1;

    sn76489_init(&psg, NTSC_Z80_CLOCK, 44100.0f, SN76489_NOISE_BITS_SMS, SN76489_NOISE_TAPPED_SMS);
    sound_init(2, SMS_VIDEO_NTSC);
    /* end sms_init */

    int done = 0,  gaw_sample = 0, gaw_size = sizeof(gaw);

    while(!done) {
        int16 buf[882 << 1];
        int  line, samples = 0;

        /* Write one sample per loop */
        if(0x80&gaw[gaw_sample]) {
            sn76489_write(&psg, gaw[gaw_sample++]);
            sn76489_write(&psg, gaw[gaw_sample++]);
        } else {
            sn76489_write(&psg, gaw[gaw_sample++]);
        }
        /* Only play ¼ of the sample for now */
        if(gaw_sample > gaw_size/4) {
            done = 1;
        }

        /* From sms_frame */
        for(line = 0; line < NTSC_LINES_PER_FRAME; line++) {
            if(sms_psg_enabled) {
                sn76489_execute_samples(&psg, buf + samples, psg_samples[line]);
            }

            while(SDL_PollEvent(&event)) {
                switch(event.type) {
                    case SDL_KEYDOWN: {
                        SDL_Keycode k = event.key.keysym.sym;
                        if(k == SDLK_ESCAPE) {
                            done = 1;
                        }
                    }
                    break;
                    case SDL_QUIT:
                        done = 1;
                        break;
                }
            }

            samples += psg_samples[line] << 1;
        }

        if(sms_psg_enabled) {
            sound_update_buffer(buf, samples << 1);
            sound_wait();
        }
        SDL_Delay(emu_delay());
    }

    sound_pause();
    sound_shutdown();
    return 0;
}