Shamusworld >> Repos - stargem2/blob - src/sound.cpp

   1 //
   2 // Sound Interface v2.0
   3 //
   4 // by James L. Hammons
   5 // (c) 2006 Underground Software
   6 //
   7 // JLH = James L. Hammons <jlhamm@acm.org>
   8 //
   9 // WHO  WHEN        WHAT
  10 // ---  ----------  ------------------------------------------------------------
  11 // JLH  06/15/2006  Added changelog ;-)
  12 // JLH  06/15/2006  Scrubbed all BYTE, WORD & DWORD references from the code
  13 // JLH  02/10/2009  Fixed sound IRQ callback so that CPU samples are taken at
  14 //                  cycle exact boundaries
  15 // JLH  07/21/2009  Moved numeric constants into macros for sanity's sake
  16 //
  17 // Notes:
  18 //   The sound CPU (6808) runs at 894,750 (3,579,000 / 4) Hz.
  19 //   At 44.1 KHz, this works out to 894750 / 44100 = 20.289115646... cycles per sample.
  20 //
  21
  22 // Still need to add volume control...
  23
  24 #include "sound.h"
  25
  26 #include "SDL.h"
  27 #include "types.h"
  28 #include "log.h"
  29 #include "v6808.h"
  30 #include "timing.h"
  31
  32 //using namespace std;
  33
  34 //#define AUDIO_SAMPLE_RATE                             44100.0
  35 #define AUDIO_SAMPLE_RATE                               48000.0
  36 #define CYCLES_TO_EXECUTE                               (M6808_CLOCK_SPEED_IN_HZ / AUDIO_SAMPLE_RATE)
  37
  38 // Local variables
  39
  40 static SDL_AudioSpec desired;
  41 static bool soundInitialized = false;
  42 static uint32 cyclesToExecuteWholePart;
  43 static double cyclesToExecuteFractionalPart;
  44
  45 // Private function prototypes
  46
  47 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length);
  48
  49 //
  50 // Initialize the SDL sound system
  51 //
  52 void SoundInit(void)
  53 {
  54 //      memory_malloc_secure((void **)&DACBuffer, BUFFER_SIZE * sizeof(uint16), "DAC buffer");
  55
  56         desired.freq = AUDIO_SAMPLE_RATE;                               // SDL will do conversion on the fly, if it can't get the exact rate. Nice!
  57         desired.format = AUDIO_U8;                                              // This uses the native endian (for portability)...
  58         desired.channels = 1;
  59 //      desired.samples = 4096;                                                 // Let's try a 4K buffer (can always go lower)
  60         desired.samples = 2048;                                                 // Let's try a 2K buffer (can always go lower)
  61         desired.callback = SDLSoundCallback;
  62
  63         if (SDL_OpenAudio(&desired, NULL) < 0)                  // NULL means SDL guarantees what we want
  64         {
  65                 WriteLog("Sound: Failed to initialize SDL sound.\n");
  66                 return;
  67         }
  68
  69         // Setup clock cycles & etc.
  70         cyclesToExecuteWholePart = (uint32)CYCLES_TO_EXECUTE;
  71         cyclesToExecuteFractionalPart = CYCLES_TO_EXECUTE - (double)cyclesToExecuteWholePart;
  72 #if 0
  73 printf("Cycles to execute: %lf; cycles W: %u; cycles F: %lf\n", CYCLES_TO_EXECUTE, cyclesToExecuteWholePart, cyclesToExecuteFractionalPart);
  74 #endif
  75
  76         SDL_PauseAudio(false);                                                  // Start playback!
  77         soundInitialized = true;
  78         WriteLog("Sound: Successfully initialized.\n");
  79 }
  80
  81 //
  82 // Close down the SDL sound subsystem
  83 //
  84 void SoundDone(void)
  85 {
  86         if (soundInitialized)
  87         {
  88                 SDL_PauseAudio(true);
  89                 SDL_CloseAudio();
  90                 WriteLog("Sound: Done.\n");
  91         }
  92 }
  93
  94 //
  95 // Sound card callback handler
  96 //
  97 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length)
  98 {
  99         extern V6808REGS soundCPU;
 100         extern uint8 sram[];
 101         int cnt = 0;
 102
 103         static float overflow = 0.0;
 104         static uint32 time = cyclesToExecuteWholePart;
 105
 106         while (cnt != length)
 107         {
 108                 Execute6808(&soundCPU, time);
 109                 soundCPU.clock -= time;
 110                 buffer[cnt++] = sram[0x0400];                           // Fill the buffer with the PIA output value
 111                 time = cyclesToExecuteWholePart;
 112                 overflow += cyclesToExecuteFractionalPart;
 113
 114                 if (overflow > 1.0)
 115                 {
 116                         overflow -= 1.0;
 117                         time++;
 118                 }
 119         }
 120 }