Genesis-Plus-GX/source/gx/gx_audio.c

/****************************************************************************
 *  gx_audio.c
 *
 *  Genesis Plus GX audio support
 *
 *  Softdev (2006)
 *  Eke-Eke (2007,2008,2009)
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 ***************************************************************************/

#include "shared.h"

/* DMA soundbuffers (required to be 32-bytes aligned)
   Length is dimensionned for one frame of emulation (800/808 samples @60hz, 960 samples@50Hz)
   To prevent audio clashes, we use double buffering technique:
    one buffer is the active DMA buffer
    the other one is the current work buffer (updated during frame emulation)
   We do not need more since frame emulation and DMA operation are synchronized
*/
u8 soundbuffer[2][3840] ATTRIBUTE_ALIGN(32);

/* Current work soundbuffer */
u8 mixbuffer;

/* audio DMA status */
static u8 audioStarted = 0;

/* Background music */
static u8 *Bg_music_ogg = NULL;
static u32 Bg_music_ogg_size = 0;

/***************************************************************************************/
/*   Audio engine                                                                      */
/***************************************************************************************/

/* Audio DMA callback */
static void ai_callback(void)
{
  frameticker++;
}

/* AUDIO engine initialization */
void gx_audio_Init(void)
{
  /* Initialize AUDIO hardware */
  /* Default samplerate is 48kHZ */
  /* Default DMA callback is programmed */
  ASND_Init();

  /* Load background music from FAT device */
  char fname[MAXPATHLEN];
  sprintf(fname,"%s/Bg_music.ogg",DEFAULT_PATH);
  FILE *f = fopen(fname,"rb");
  if (f)
  {
    struct stat filestat;
    stat(fname, &filestat);
    Bg_music_ogg_size = filestat.st_size;
    Bg_music_ogg = memalign(32,Bg_music_ogg_size);
    if (Bg_music_ogg) fread(Bg_music_ogg,1,Bg_music_ogg_size,f);
    fclose(f);
  }
}

/* AUDIO engine shutdown */
void gx_audio_Shutdown(void)
{
  PauseOgg(1);
  StopOgg();
  ASND_Pause(1);
  ASND_End();
  if (Bg_music_ogg) free(Bg_music_ogg);
}

/*** 
      gx_audio_Update

     This function retrieves samples for the frame then set the next DMA parameters 
     Parameters will be taken in account only when current DMA operation is over
 ***/
void gx_audio_Update(int size)
{
  /* set next DMA soundbuffer */
  s16 *sb = (s16 *)(soundbuffer[mixbuffer]);
  mixbuffer ^= 1;
  DCFlushRange((void *)sb, size);
  AUDIO_InitDMA((u32) sb, size);

  /* Start Audio DMA */
  /* this is only called once, DMA being automatically restarted when previous one is over */
  /* If DMA settings are not updated at that time, the same soundbuffer will be played again */
  if (!audioStarted)
  {
    audioStarted = 1;
    AUDIO_StartDMA();
    if (frameticker > 1)
      frameticker = 1;
  }
}

/*** 
      gx_audio_Start

     This function restart the audio engine
     This is called when coming back from Main Menu
 ***/
void gx_audio_Start(void)
{
  /* shutdown menu audio */
  PauseOgg(1);
  StopOgg();
  ASND_Pause(1);
  ASND_End();
  audioStarted = 0;
  mixbuffer = 0;

  /* reset sound buffers */
  memset(soundbuffer, 0, 2 * 3840);

  /* By default, use audio DMA to synchronize frame emulation */
  if (gc_pal | vdp_pal)
    AUDIO_RegisterDMACallback(ai_callback);
}

/***
      gx_audio_Stop

     This function stops current Audio DMA process
     This is called when going back to Main Menu
     DMA need to be restarted when going back to the game (see above)
 ***/
void gx_audio_Stop(void)
{
  /* restart menu audio (this will automatically stops current audio DMA) */
  ASND_Init();
  ASND_Pause(0);
  if (Bg_music_ogg && !Shutdown)
  {
    PauseOgg(0);
    PlayOgg((char *)Bg_music_ogg, Bg_music_ogg_size, 0, OGG_INFINITE_TIME);
    SetVolumeOgg(((int)config.bgm_volume * 255) / 100);
  }
}