2 // Sound Interface v2.0
5 // (c) 2006 Underground Software
7 // JLH = James Hammons <jlhamm@acm.org>
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
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
23 // Still need to add volume control...
33 //using namespace std;
35 #define AUDIO_SAMPLE_RATE 48000.0
36 #define CYCLES_TO_EXECUTE (M6808_CLOCK_SPEED_IN_HZ / AUDIO_SAMPLE_RATE)
40 static SDL_AudioSpec desired;
41 static bool soundInitialized = false;
42 static uint32_t cyclesToExecuteWholePart;
43 static double cyclesToExecuteFractionalPart;
45 // Private function prototypes
47 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length);
50 // Initialize the SDL sound system
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)...
57 desired.samples = 2048; // Let's try a 2K buffer (can always go lower)
58 desired.callback = SDLSoundCallback;
60 if (SDL_OpenAudio(&desired, NULL) < 0) // NULL means SDL guarantees what we want
62 WriteLog("Sound: Failed to initialize SDL sound.\n");
66 // Setup clock cycles & etc.
67 cyclesToExecuteWholePart = (uint32_t)CYCLES_TO_EXECUTE;
68 cyclesToExecuteFractionalPart = CYCLES_TO_EXECUTE - (double)cyclesToExecuteWholePart;
70 SDL_PauseAudio(false); // Start playback!
71 soundInitialized = true;
72 WriteLog("Sound: Successfully initialized.\n");
76 // Close down the SDL sound subsystem
84 WriteLog("Sound: Done.\n");
89 // Sound card callback handler
91 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length)
93 extern V6808REGS soundCPU;
94 extern uint8_t sram[];
97 static float overflow = 0.0;
98 static uint32_t time = cyclesToExecuteWholePart;
100 while (cnt != length)
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;