/*****************************************************************************/
/*                                                                           */
/* Module:  TIA Chip Sound Simulator, V1.0                                   */
/* Purpose: To emulate the sound generation hardware of the Atari TIA chip.  */
/* Author:  Ron Fries                                                        */
/* Date:    September 10, 1996                                               */
/*                                                                           */
/*****************************************************************************/
/*                                                                           */
/*                 License Information and Copyright Notice                  */
/*                 ========================================                  */
/*                                                                           */
/* TiaSound is Copyright(c) 1996 by Ron Fries                                */
/*                                                                           */
/* This library is free software; you can redistribute it and/or modify it   */
/* under the terms of version 2 of the GNU Library General Public License    */
/* as published by the Free Software Foundation.                             */
/*                                                                           */
/* This library is distributed in the hope that it will be useful, but       */
/* WITHOUT ANY WARRANTY; without even the implied warranty of                */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library */
/* General Public License for more details.                                  */
/* To obtain a copy of the GNU Library General Public License, write to the  */
/* Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.   */
/*                                                                           */
/* Any permitted reproduction of these routines, in whole or in part, must   */
/* bear this legend.                                                         */
/*                                                                           */
/*****************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <time.h>


/* define some data types to keep it platform independent */
#define int8  char
#define int16 short
#define int32 int

#define uint8  unsigned int8 
#define uint16 unsigned int16
#define uint32 unsigned int32


/* CONSTANT DEFINITIONS */

/* definitions for AUDCx (15, 16) */
#define SET_TO_1     0x00      /* 0000 */
#define POLY4        0x01      /* 0001 */
#define DIV31_POLY4  0x02      /* 0010 */
#define POLY5_POLY4  0x03      /* 0011 */
#define PURE         0x04      /* 0100 */
#define PURE2        0x05      /* 0101 */
#define DIV31_PURE   0x06      /* 0110 */
#define POLY5_2      0x07      /* 0111 */
#define POLY9        0x08      /* 1000 */
#define POLY5        0x09      /* 1001 */
#define DIV31_POLY5  0x0a      /* 1010 */
#define POLY5_POLY5  0x0b      /* 1011 */
#define DIV3_PURE    0x0c      /* 1100 */
#define DIV3_PURE2   0x0d      /* 1101 */
#define DIV93_PURE   0x0e      /* 1110 */
#define DIV3_POLY5   0x0f      /* 1111 */
                 
#define DIV3_MASK    0x0c                 
                 
#define AUDC0        0x15
#define AUDC1        0x16
#define AUDF0        0x17
#define AUDF1        0x18
#define AUDV0        0x19
#define AUDV1        0x1a

/* the size (in entries) of the 4 polynomial tables */
#define POLY4_SIZE  0x000f
#define POLY5_SIZE  0x001f
#define POLY9_SIZE  0x01ff

/* channel definitions */
#define CHAN1       0
#define CHAN2       1

#define FALSE       0
#define TRUE        1


/* LOCAL GLOBAL VARIABLE DEFINITIONS */

/* structures to hold the 6 tia sound control bytes */
static uint8 AUDC[2];    /* AUDCx (15, 16) */
static uint8 AUDF[2];    /* AUDFx (17, 18) */
static uint8 AUDV[2];    /* AUDVx (19, 1A) */

static uint8 Outvol[2];  /* last output volume for each channel */


/* Initialze the bit patterns for the polynomials. */

/* The 4bit and 5bit patterns are the identical ones used in the tia chip. */
/* Though the patterns could be packed with 8 bits per byte, using only a */
/* single bit per byte keeps the math simple, which is important for */
/* efficient processing. */

static uint8 Bit4[POLY4_SIZE] =
      { 1,1,0,1,1,1,0,0,0,0,1,0,1,0,0 };

static uint8 Bit5[POLY5_SIZE] =
      { 0,0,1,0,1,1,0,0,1,1,1,1,1,0,0,0,1,1,0,1,1,1,0,1,0,1,0,0,0,0,1 };

/* I've treated the 'Div by 31' counter as another polynomial because of */
/* the way it operates.  It does not have a 50% duty cycle, but instead */
/* has a 13:18 ratio (of course, 13+18 = 31).  This could also be */
/* implemented by using counters. */

static uint8 Div31[POLY5_SIZE] =
      { 0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0 };

/* Rather than have a table with 511 entries, I use a random number */
/* generator. */

static uint8 Bit9[POLY9_SIZE];

static uint8  P4[2]; /* Position pointer for the 4-bit POLY array */
static uint8  P5[2]; /* Position pointer for the 5-bit POLY array */
static uint16 P9[2]; /* Position pointer for the 9-bit POLY array */

static uint8 Div_n_cnt[2];  /* Divide by n counter. one for each channel */
static uint8 Div_n_max[2];  /* Divide by n maximum, one for each channel */


/* In my routines, I treat the sample output as another divide by N counter. */
/* For better accuracy, the Samp_n_cnt has a fixed binary decimal point */
/* which has 8 binary digits to the right of the decimal point. */

static uint16 Samp_n_max; /* Sample max, multiplied by 256 */
static uint16 Samp_n_cnt; /* Sample cnt. */



/*****************************************************************************/
/* Module:  Tia_sound_init()                                                 */
/* Purpose: to handle the power-up initialization functions                  */
/*          these functions should only be executed on a cold-restart        */
/*                                                                           */
/* Author:  Ron Fries                                                        */
/* Date:    September 10, 1996                                               */
/*                                                                           */
/* Inputs:  sample_freq - the value for the '30 Khz' Tia audio clock         */
/*          playback_freq - the playback frequency in samples per second     */
/*                                                                           */
/* Outputs: Adjusts local globals - no return value                          */
/*                                                                           */
/*****************************************************************************/

void Tia_sound_init (uint16 sample_freq, uint16 playback_freq)
{
   uint8 chan;
   int16 n;

   /* fill the 9bit polynomial with random bits */
   for (n=0; n<POLY9_SIZE; n++)
   {
      Bit9[n] = rand() & 0x01;       /* fill poly9 with random bits */
   }

   /* calculate the sample 'divide by N' value based on the playback freq. */
   Samp_n_max = (uint16)(((uint32)sample_freq<<8)/playback_freq);
   Samp_n_cnt = 0;  /* initialize all bits of the sample counter */

   /* initialize the local globals */
   for (chan = CHAN1; chan <= CHAN2; chan++)
   {
      Outvol[chan] = 0;
      Div_n_cnt[chan] = 0;
      Div_n_max[chan] = 0;
      AUDC[chan] = 0;
      AUDF[chan] = 0;
      AUDV[chan] = 0;
      P4[chan] = 0;
      P5[chan] = 0;
      P9[chan] = 0;
   }
}


/*****************************************************************************/
/* Module:  Update_tia_sound()                                               */
/* Purpose: To process the latest control values stored in the AUDF, AUDC,   */
/*          and AUDV registers.  It pre-calculates as much information as    */
/*          possible for better performance.  This routine has not been      */
/*          optimized.                                                       */
/*                                                                           */
/* Author:  Ron Fries                                                        */
/* Date:    September 10, 1996                                               */
/*                                                                           */
/* Inputs:  addr - the address of the parameter to be changed                */
/*          val - the new value to be placed in the specified address        */
/*                                                                           */
/* Outputs: Adjusts local globals - no return value                          */
/*                                                                           */
/*****************************************************************************/

void Update_tia_sound (uint16 addr, uint8 val)
{
    uint16 new_val = 0;
    uint8 chan;

    /* determine which address was changed */
    switch (addr)
    {
       case AUDC0:
          AUDC[0] = val & 0x0f;
          chan = 0;
          break;

       case AUDC1:
          AUDC[1] = val & 0x0f;
          chan = 1;
          break;

       case AUDF0:
          AUDF[0] = val & 0x1f;
          chan = 0;
          break;

       case AUDF1:
          AUDF[1] = val & 0x1f;
          chan = 1;
          break;

       case AUDV0:
          AUDV[0] = (val & 0x0f) << 3;
          chan = 0;
          break;

       case AUDV1:
          AUDV[1] = (val & 0x0f) << 3;
          chan = 1;
          break;

       default:
          chan = 255;
          break;
    }

    /* if the output value changed */
    if (chan != 255)
    {
       /* an AUDC value of 0 is a special case */
       if (AUDC[chan] == SET_TO_1)
       {
          /* indicate the clock is zero so no processing will occur */
          new_val = 0;

          /* and set the output to the selected volume */
          Outvol[chan] = AUDV[chan];
       }
       else
       {
          /* otherwise calculate the 'divide by N' value */
          new_val = AUDF[chan] + 1;

          /* if bits 2 & 3 are set, then multiply the 'div by n' count by 3 */
          if ((AUDC[chan] & DIV3_MASK) == DIV3_MASK)
          {
             new_val *= 3;
          }
       }

       /* only reset those channels that have changed */
       if (new_val != Div_n_max[chan])
       {
          /* reset the divide by n counters */
          Div_n_max[chan] = new_val;
          Div_n_cnt[chan] = new_val;

          /* reset the polynomial counters */
          P4[chan] = 0;
          P5[chan] = 0;
          P9[chan] = 0;
       }
    }
}


/*****************************************************************************/
/* Module:  Tia_process_2()                                                  */
/* Purpose: To fill the output buffer with the sound output based on the     */
/*          tia chip parameters.  This routine has not been optimized.       */
/*          Though it is not used by the program, I've left it for reference.*/
/*                                                                           */
/* Author:  Ron Fries                                                        */
/* Date:    September 10, 1996                                               */
/*                                                                           */
/* Inputs:  *buffer - pointer to the buffer where the audio output will      */
/*                    be placed                                              */
/*          n - size of the playback buffer                                  */
/*                                                                           */
/* Outputs: the buffer will be filled with n bytes of audio - no return val  */
/*                                                                           */
/*****************************************************************************/

void Tia_process_2 (register unsigned char *buffer, register uint16 n)
{
    register uint8 chan;

    /* loop until the buffer is filled */
    while (n)
    {
       /* loop through the channels */
       for (chan = CHAN1; chan <= CHAN2; chan++)
       {
          /* NOTE: this routine intentionally does not count down to zero */
          /* since 0 is used as a special case - no clock */

          /* if the divide by N counter can count down */
          if (Div_n_cnt[chan] > 1)
          {
             /* decrement and loop */
             Div_n_cnt[chan]--;
          }
          /* otherwise if we've reached the bottom */
          else if (Div_n_cnt[chan] == 1)
          {
             /* reset the counter */
             Div_n_cnt[chan] = Div_n_max[chan];

             /* the P5 counter has multiple uses, so we inc it here */
             P5[chan]++;
             if (P5[chan] == POLY5_SIZE)
                P5[chan] = 0;

             /* check clock modifier for clock tick */

             /* if we're using pure tones OR
                   we're using DIV31 and the DIV31 bit is set OR
                   we're using POLY5 and the POLY5 bit is set */
             if  (((AUDC[chan] & 0x02) == 0) ||
                 (((AUDC[chan] & 0x01) == 0) && Div31[P5[chan]]) ||
                 (((AUDC[chan] & 0x01) == 1) &&  Bit5[P5[chan]]))
             {
                if (AUDC[chan] & 0x04)       /* pure modified clock selected */
                {
                   if (Outvol[chan])         /* if the output was set */
                      Outvol[chan] = 0;      /* turn it off */
                   else
                      Outvol[chan] = AUDV[chan];   /* else turn it on */
                }
                else if (AUDC[chan] & 0x08)  /* check for p5/p9 */
                {
                   if (AUDC[chan] == POLY9)  /* check for poly9 */
                   {
                      /* inc the poly9 counter */
                      P9[chan]++;
                      if (P9[chan] == POLY9_SIZE)
                         P9[chan] = 0;

                      if (Bit9[P9[chan]])    /* if poly9 bit is set */
                         Outvol[chan] = AUDV[chan];
                      else
                         Outvol[chan] = 0;
                   }
                   else                      /* must be poly5 */
                   {
                      if (Bit5[P5[chan]])
                         Outvol[chan] = AUDV[chan];
                      else
                         Outvol[chan] = 0;
                   }
                }
                else  /* poly4 is the only remaining option */
                {
                   /* inc the poly4 counter */
                   P4[chan]++;
                   if (P4[chan] == POLY4_SIZE)
                      P4[chan] = 0;

                   if (Bit4[P4[chan]])
                      Outvol[chan] = AUDV[chan];
                   else
                      Outvol[chan] = 0;
                }
             }
          }
       }

       /* decrement the sample counter - value is 256 since the lower
          byte contains the fractional part */
       Samp_n_cnt -= 256;

       /* if the count down has reached zero */
       if (Samp_n_cnt < 256)
       {
          /* adjust the sample counter */
          Samp_n_cnt += Samp_n_max;

          /* calculate the latest output value and place in buffer */
          *(buffer++) = Outvol[0] + Outvol[1];

          /* and indicate one less byte to process */
          n--;
       }
    }
}


/*****************************************************************************/
/* Module:  Tia_process()                                                    */
/* Purpose: To fill the output buffer with the sound output based on the     */
/*          tia chip parameters.  This routine has been optimized.           */
/*                                                                           */
/* Author:  Ron Fries                                                        */
/* Date:    September 10, 1996                                               */
/*                                                                           */
/* Inputs:  *buffer - pointer to the buffer where the audio output will      */
/*                    be placed                                              */
/*          n - size of the playback buffer                                  */
/*                                                                           */
/* Outputs: the buffer will be filled with n bytes of audio - no return val  */
/*                                                                           */
/*****************************************************************************/

void Tia_process (register unsigned char *buffer, register uint16 n)
{
    register uint8 audc0,audv0,audc1,audv1;
    register uint8 div_n_cnt0,div_n_cnt1;
    register uint8 p5_0, p5_1,outvol_0,outvol_1;

    audc0 = AUDC[0];
    audv0 = AUDV[0];
    audc1 = AUDC[1];
    audv1 = AUDV[1];

    /* make temporary local copy */
    p5_0 = P5[0];
    p5_1 = P5[1];
    outvol_0 = Outvol[0];
    outvol_1 = Outvol[1];
    div_n_cnt0 = Div_n_cnt[0];
    div_n_cnt1 = Div_n_cnt[1];

    /* loop until the buffer is filled */
    while (n)
    {
       /* Process channel 0 */
       if (div_n_cnt0 > 1)
       {
          div_n_cnt0--;
       }
       else if (div_n_cnt0 == 1)
       {
          div_n_cnt0 = Div_n_max[0];

          /* the P5 counter has multiple uses, so we inc it here */
          p5_0++;
          if (p5_0 == POLY5_SIZE)
             p5_0 = 0;

          /* check clock modifier for clock tick */
          if  (((audc0 & 0x02) == 0) ||
              (((audc0 & 0x01) == 0) && Div31[p5_0]) ||
              (((audc0 & 0x01) == 1) &&  Bit5[p5_0]))
          {
             if (audc0 & 0x04)       /* pure modified clock selected */
             {
                if (outvol_0)        /* if the output was set */
                   outvol_0 = 0;     /* turn it off */
                else
                   outvol_0 = audv0; /* else turn it on */
             }
             else if (audc0 & 0x08)    /* check for p5/p9 */
             {
                if (audc0 == POLY9)    /* check for poly9 */
                {
                   /* inc the poly9 counter */
                   P9[0]++;
                   if (P9[0] == POLY9_SIZE)
                      P9[0] = 0;

                   if (Bit9[P9[0]])
                      outvol_0 = audv0;
                   else
                      outvol_0 = 0;
                }
                else                        /* must be poly5 */
                {
                   if (Bit5[p5_0])
                      outvol_0 = audv0;
                   else
                      outvol_0 = 0;
                }
             }
             else  /* poly4 is the only remaining option */
             {
                /* inc the poly4 counter */
                P4[0]++;
                if (P4[0] == POLY4_SIZE)
                   P4[0] = 0;

                if (Bit4[P4[0]])
                   outvol_0 = audv0;
                else
                   outvol_0 = 0;
             }
          }
       }


       /* Process channel 1 */
       if (div_n_cnt1 > 1)
       {
          div_n_cnt1--;
       }
       else if (div_n_cnt1 == 1)
       {
          div_n_cnt1 = Div_n_max[1];

          /* the P5 counter has multiple uses, so we inc it here */
          p5_1++;
          if (p5_1 == POLY5_SIZE)
             p5_1 = 0;

          /* check clock modifier for clock tick */
          if  (((audc1 & 0x02) == 0) ||
              (((audc1 & 0x01) == 0) && Div31[p5_1]) ||
              (((audc1 & 0x01) == 1) &&  Bit5[p5_1]))
          {
             if (audc1 & 0x04)       /* pure modified clock selected */
             {
                if (outvol_1)        /* if the output was set */
                   outvol_1 = 0;     /* turn it off */
                else
                   outvol_1 = audv1; /* else turn it on */
             }
             else if (audc1 & 0x08)    /* check for p5/p9 */
             {
                if (audc1 == POLY9)    /* check for poly9 */
                {
                   /* inc the poly9 counter */
                   P9[1]++;
                   if (P9[1] == POLY9_SIZE)
                      P9[1] = 0;

                   if (Bit9[P9[1]])
                      outvol_1 = audv1;
                   else
                      outvol_1 = 0;
                }
                else                        /* must be poly5 */
                {
                   if (Bit5[p5_1])
                      outvol_1 = audv1;
                   else
                      outvol_1 = 0;
                }
             }
             else  /* poly4 is the only remaining option */
             {
                /* inc the poly4 counter */
                P4[1]++;
                if (P4[1] == POLY4_SIZE)
                   P4[1] = 0;

                if (Bit4[P4[1]])
                   outvol_1 = audv1;
                else
                   outvol_1 = 0;
             }
          }
       }

       /* decrement the sample counter - value is 256 since the lower
          byte contains the fractional part */
       Samp_n_cnt -= 256;

       /* if the count down has reached zero */
       if (Samp_n_cnt < 256)
       {
          /* adjust the sample counter */
          Samp_n_cnt += Samp_n_max;

          /* calculate the latest output value and place in buffer */
          *(buffer++) = outvol_0 + outvol_1;

          /* and indicate one less byte to process */
          n--;
       }
    }

    /* save for next round */
    P5[0] = p5_0;
    P5[1] = p5_1;
    Outvol[0] = outvol_0;
    Outvol[1] = outvol_1;
    Div_n_cnt[0] = div_n_cnt0;
    Div_n_cnt[1] = div_n_cnt1;

}