Shamusworld >> Repos - virtualjaguar/blob - src/dac.cpp

   1 //
   2 // DAC (really, Synchronous Serial Interface) Handler
   3 //
   4 // by cal2
   5 // GCC/SDL port by Niels Wagenaar (Linux/WIN32) and Caz (BeOS)
   6 // Rewritten by James L. Hammons
   7 //
   8
   9 #include <SDL.h>
  10 #include "jaguar.h"
  11 #include "dac.h"
  12 #include "settings.h"
  13
  14 //#define DEBUG_DAC
  15
  16 #define BUFFER_SIZE             0x8000                                          // Make the DAC buffers 32K x 16 bits
  17
  18 // Jaguar memory locations
  19
  20 #define LTXD                    0xF1A148
  21 #define RTXD                    0xF1A14C
  22 #define SCLK                    0xF1A150
  23 #define SMODE                   0xF1A154
  24
  25 // Local variables
  26
  27 uint32 LeftFIFOHeadPtr, LeftFIFOTailPtr, RightFIFOHeadPtr, RightFIFOTailPtr;
  28 SDL_AudioSpec desired;
  29
  30 // We can get away with using native endian here because we can tell SDL to use the native
  31 // endian when looking at the sample buffer, i.e., no need to worry about it.
  32
  33 uint16 * DACBuffer;
  34 uint8 SCLKFrequencyDivider = 19;                                                // Default is roughly 22 KHz (20774 Hz in NTSC mode)
  35 uint16 serialMode = 0;
  36
  37 // Private function prototypes
  38
  39 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length);
  40 int GetCalculatedFrequency(void);
  41
  42 //
  43 // Initialize the SDL sound system (?) (!)
  44 //
  45 void DACInit(void)
  46 {
  47         memory_malloc_secure((void **)&DACBuffer, BUFFER_SIZE * sizeof(uint16), "DAC buffer");
  48
  49         desired.freq = GetCalculatedFrequency();                // SDL will do conversion on the fly, if it can't get the exact rate. Nice!
  50         desired.format = AUDIO_S16SYS;                                  // This uses the native endian (for portability)...
  51         desired.channels = 2;
  52         desired.samples = 4096;                                                 // Let's try a 4K buffer (can always go lower)
  53         desired.callback = SDLSoundCallback;
  54
  55         if (SDL_OpenAudio(&desired, NULL) < 0)                  // NULL means SDL guarantees what we want
  56         {
  57                 WriteLog("DAC: Failed to initialize SDL sound. Shutting down!\n");
  58                 log_done();
  59                 exit(1);
  60         }
  61
  62         DACReset();
  63         SDL_PauseAudio(false);                                                  // Start playback!
  64         WriteLog("DAC: Successfully initialized.\n");
  65 }
  66
  67 //
  68 // Reset the sound buffer FIFOs
  69 //
  70 void DACReset(void)
  71 {
  72         LeftFIFOHeadPtr = LeftFIFOTailPtr = 0, RightFIFOHeadPtr = RightFIFOTailPtr = 1;
  73 }
  74
  75 //
  76 // Close down the SDL sound subsystem (?) (!)
  77 //
  78 void DACDone(void)
  79 {
  80         SDL_PauseAudio(true);
  81         SDL_CloseAudio();
  82         WriteLog("DAC: Done.\n");
  83 }
  84
  85 //
  86 // SDL callback routine to fill audio buffer
  87 //
  88 // Note: The samples are packed in the buffer in 16 bit left/16 bit right pairs.
  89 //
  90 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length)
  91 {
  92         // Clear the buffer to silence, in case the DAC buffer is empty (or short)
  93         memset(buffer, desired.silence, length);
  94 //WriteLog("DAC: Inside callback...\n");
  95         if (LeftFIFOHeadPtr != LeftFIFOTailPtr)
  96         {
  97 //WriteLog("DAC: About to write some data!\n");
  98                 int numLeftSamplesReady
  99                         = (LeftFIFOTailPtr + (LeftFIFOTailPtr < LeftFIFOHeadPtr ? BUFFER_SIZE : 0))
 100                                 - LeftFIFOHeadPtr;
 101                 int numRightSamplesReady
 102                         = (RightFIFOTailPtr + (RightFIFOTailPtr < RightFIFOHeadPtr ? BUFFER_SIZE : 0))
 103                                 - RightFIFOHeadPtr;
 104                 int numSamplesReady
 105                         = (numLeftSamplesReady < numRightSamplesReady
 106                                 ? numLeftSamplesReady : numRightSamplesReady);//Hmm. * 2;
 107
 108 //The numbers look good--it's just that the DSP can't get enough samples in the DAC buffer!
 109 //WriteLog("DAC: Left/RightFIFOHeadPtr: %u/%u, Left/RightFIFOTailPtr: %u/%u\n", LeftFIFOHeadPtr, RightFIFOHeadPtr, LeftFIFOTailPtr, RightFIFOTailPtr);
 110 //WriteLog("     numLeft/RightSamplesReady: %i/%i, numSamplesReady: %i, length of buffer: %i\n", numLeftSamplesReady, numRightSamplesReady, numSamplesReady, length);
 111
 112 /*              if (numSamplesReady > length)
 113                         numSamplesReady = length;//*/
 114                 if (numSamplesReady > length / 2)       // length / 2 because we're comparing 16-bit lengths
 115                         numSamplesReady = length / 2;
 116 //else
 117 //      WriteLog("     Not enough samples to fill the buffer (short by %u L/R samples)...\n", (length / 2) - numSamplesReady);
 118 //WriteLog("DAC: %u samples ready.\n", numSamplesReady);
 119
 120                 // Actually, it's a bit more involved than this, but this is the general idea:
 121 //              memcpy(buffer, DACBuffer, length);
 122                 for(int i=0; i<numSamplesReady; i++)
 123                         // Could also use (as long as BUFFER_SIZE is a multiple of 2):
 124                         ((uint16 *)buffer)[i] = DACBuffer[(LeftFIFOHeadPtr + i) % BUFFER_SIZE];
 125 //                      buffer[i] = DACBuffer[(LeftFIFOHeadPtr + i) & (BUFFER_SIZE - 1)];
 126
 127                 LeftFIFOHeadPtr = (LeftFIFOHeadPtr + numSamplesReady) % BUFFER_SIZE;
 128                 RightFIFOHeadPtr = (RightFIFOHeadPtr + numSamplesReady) % BUFFER_SIZE;
 129                 // Could also use (as long as BUFFER_SIZE is a multiple of 2):
 130 //              LeftFIFOHeadPtr = (LeftFIFOHeadPtr + (numSamplesReady)) & (BUFFER_SIZE - 1);
 131 //              RightFIFOHeadPtr = (RightFIFOHeadPtr + (numSamplesReady)) & (BUFFER_SIZE - 1);
 132 //WriteLog("  -> Left/RightFIFOHeadPtr: %u/%u, Left/RightFIFOTailPtr: %u/%u\n", LeftFIFOHeadPtr, RightFIFOHeadPtr, LeftFIFOTailPtr, RightFIFOTailPtr);
 133         }
 134 //Hmm. Seems that the SDL buffer isn't being starved by the DAC buffer...
 135 //      else
 136 //              WriteLog("DAC: Silence...!\n");
 137 }
 138
 139 //
 140 // Calculate the frequency of SCLK * 32 using the divider
 141 //
 142 int GetCalculatedFrequency(void)
 143 {
 144 //      extern bool hardwareTypeNTSC;
 145         int systemClockFrequency = (vjs.hardwareTypeNTSC ? RISC_CLOCK_RATE_NTSC : RISC_CLOCK_RATE_PAL);
 146
 147         // We divide by 32 here in order to find the frequency of 32 SCLKs in a row (transferring
 148         // 16 bits of left data + 16 bits of right data = 32 bits, 1 SCLK = 1 bit transferred).
 149         return systemClockFrequency / (32 * (2 * (SCLKFrequencyDivider + 1)));
 150 }
 151
 152 //
 153 // LTXD/RTXD/SCLK/SMODE ($F1A148/4C/50/54)
 154 //
 155 void DACWriteByte(uint32 offset, uint8 data)
 156 {
 157         WriteLog("DAC: Writing %02X at %08X\n", data, offset);
 158         if (offset == SCLK + 3)
 159                 DACWriteWord(offset - 3, (uint16)data);
 160 }
 161
 162 void DACWriteWord(uint32 offset, uint16 data)
 163 {
 164         if (offset == LTXD + 2)
 165         {
 166                 if (LeftFIFOTailPtr + 2 != LeftFIFOHeadPtr)
 167                 {
 168                         SDL_LockAudio();                                                // Is it necessary to do this? Mebbe.
 169                         // We use a circular buffer 'cause it's easy. Note that the callback function
 170                         // takes care of dumping audio to the soundcard...! Also note that we're writing
 171                         // the samples in the buffer in an interleaved L/R format.
 172                         LeftFIFOTailPtr = (LeftFIFOTailPtr + 2) % BUFFER_SIZE;
 173                         DACBuffer[LeftFIFOTailPtr] = data;
 174 // Aaron's code does this, but I don't know why...
 175 //Flipping this bit makes the audio MUCH louder. Need to look at the amplitude of the
 176 //waveform to see if any massaging is needed here...
 177 //Looks like a cheap & dirty way to convert signed samples to unsigned...
 178 //                      DACBuffer[LeftFIFOTailPtr] = data ^ 0x8000;
 179                         SDL_UnlockAudio();
 180                 }
 181 #ifdef DEBUG_DAC
 182                 else
 183                         WriteLog("DAC: Ran into FIFO's left tail pointer!\n");
 184 #endif
 185         }
 186         else if (offset == RTXD + 2)
 187         {
 188                 if (RightFIFOTailPtr + 2 != RightFIFOHeadPtr)
 189                 {
 190                         SDL_LockAudio();
 191                         RightFIFOTailPtr = (RightFIFOTailPtr + 2) % BUFFER_SIZE;
 192                         DACBuffer[RightFIFOTailPtr] = data;
 193 // Aaron's code does this, but I don't know why...
 194 //                      DACBuffer[RightFIFOTailPtr] = data ^ 0x8000;
 195                         SDL_UnlockAudio();
 196                 }
 197 #ifdef DEBUG_DAC
 198                 else
 199                         WriteLog("DAC: Ran into FIFO's right tail pointer!\n");
 200 #endif
 201         }
 202         else if (offset == SCLK + 2)                                    // Sample rate
 203         {
 204                 WriteLog("DAC: Writing %u to SCLK...\n", data);
 205                 if ((uint8)data != SCLKFrequencyDivider)
 206                 {
 207                         SCLKFrequencyDivider = (uint8)data;
 208 //Of course a better way would be to query the hardware to find the upper limit...
 209                         if (data > 7)   // Anything less than 8 is too high!
 210                         {
 211                                 SDL_CloseAudio();
 212                                 desired.freq = GetCalculatedFrequency();// SDL will do conversion on the fly, if it can't get the exact rate. Nice!
 213                                 WriteLog("DAC: Changing sample rate to %u Hz!\n", desired.freq);
 214
 215                                 if (SDL_OpenAudio(&desired, NULL) < 0)  // NULL means SDL guarantees what we want
 216                                 {
 217                                         WriteLog("DAC: Failed to initialize SDL sound: %s.\nDesired freq: %u\nShutting down!\n", SDL_GetError(), desired.freq);
 218                                         log_done();
 219                                         exit(1);
 220                                 }
 221
 222                                 DACReset();
 223                                 SDL_PauseAudio(false);                          // Start playback!
 224                         }
 225                 }
 226         }
 227         else if (offset == SMODE + 2)
 228         {
 229                 serialMode = data;
 230                 WriteLog("DAC: Writing to SMODE. Bits: %s%s%s%s%s%s\n",
 231                         (data & 0x01 ? "INTERNAL " : ""), (data & 0x02 ? "MODE " : ""),
 232                         (data & 0x04 ? "WSEN " : ""), (data & 0x08 ? "RISING " : ""),
 233                         (data & 0x10 ? "FALLING " : ""), (data & 0x20 ? "EVERYWORD" : ""));
 234         }
 235 }
 236
 237 //
 238 // LRXD/RRXD/SSTAT ($F1A148/4C/50)
 239 //
 240 uint8 DACReadByte(uint32 offset)
 241 {
 242 //      WriteLog("DAC: Reading byte from %08X\n", offset);
 243         return 0xFF;
 244 }
 245
 246 uint16 DACReadWord(uint32 offset)
 247 {
 248 //      WriteLog("DAC: Reading word from %08X\n", offset);
 249         return 0xFFFF;
 250 }