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

   1 //
   2 // Sound Interface v2.0
   3 //
   4 // by James Hammons
   5 // (c) 2006 Underground Software
   6 //
   7 // JLH = James 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
  20 //   sample.
  21 //
  22
  23 // Still need to add volume control...
  24
  25 #include "sound.h"
  26
  27 #include <SDL2/SDL.h>
  28 #include <stdint.h>
  29 #include "log.h"
  30 #include "v6808.h"
  31 #include "timing.h"
  32
  33 //using namespace std;
  34
  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_t 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         desired.freq = AUDIO_SAMPLE_RATE;               // SDL will do conversion on the fly, if it can't get the exact rate. Nice!
  55         desired.format = AUDIO_U8;                              // This uses the native endian (for portability)...
  56         desired.channels = 1;
  57         desired.samples = 2048;                                 // Let's try a 2K buffer (can always go lower)
  58         desired.callback = SDLSoundCallback;
  59
  60         if (SDL_OpenAudio(&desired, NULL) < 0)  // NULL means SDL guarantees what we want
  61         {
  62                 WriteLog("Sound: Failed to initialize SDL sound.\n");
  63                 return;
  64         }
  65
  66         // Setup clock cycles & etc.
  67         cyclesToExecuteWholePart = (uint32_t)CYCLES_TO_EXECUTE;
  68         cyclesToExecuteFractionalPart = CYCLES_TO_EXECUTE - (double)cyclesToExecuteWholePart;
  69
  70         SDL_PauseAudio(false);                                                  // Start playback!
  71         soundInitialized = true;
  72         WriteLog("Sound: Successfully initialized.\n");
  73 }
  74
  75 //
  76 // Close down the SDL sound subsystem
  77 //
  78 void SoundDone(void)
  79 {
  80         if (soundInitialized)
  81         {
  82                 SDL_PauseAudio(true);
  83                 SDL_CloseAudio();
  84                 WriteLog("Sound: Done.\n");
  85         }
  86 }
  87
  88 //
  89 // Sound card callback handler
  90 //
  91 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length)
  92 {
  93         extern V6808REGS soundCPU;
  94         extern uint8_t sram[];
  95         int cnt = 0;
  96
  97         static float overflow = 0.0;
  98         static uint32_t time = cyclesToExecuteWholePart;
  99
 100         while (cnt != length)
 101         {
 102                 Execute6808(&soundCPU, time);
 103                 soundCPU.clock -= time;
 104 //              buffer[cnt++] = sram[0x0400];                           // Fill the buffer with the PIA output value
 105                 // Do some simple volume control...
 106                 buffer[cnt++] = sram[0x0400] / 4;                       // Fill the buffer with the PIA output value
 107                 time = cyclesToExecuteWholePart;
 108                 overflow += cyclesToExecuteFractionalPart;
 109
 110                 if (overflow > 1.0)
 111                 {
 112                         overflow -= 1.0;
 113                         time++;
 114                 }
 115         }
 116 }