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