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robmcmullen-apple2/src/ay8910.cpp

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/***************************************************************************
ay8910.cpp
Emulation of the AY-3-8910 / YM2149 sound chip.
Based on various code snippets by Ville Hallik, Michael Cuddy,
Tatsuyuki Satoh, Fabrice Frances, Nicola Salmoria.
***************************************************************************/
//
// From mame.txt (http://www.mame.net/readme.html)
//
// VI. Reuse of Source Code
// --------------------------
// This chapter might not apply to specific portions of MAME (e.g. CPU
// emulators) which bear different copyright notices.
// The source code cannot be used in a commercial product without the written
// authorization of the authors. Use in non-commercial products is allowed, and
// indeed encouraged. If you use portions of the MAME source code in your
// program, however, you must make the full source code freely available as
// well.
// Usage of the _information_ contained in the source code is free for any use.
// However, given the amount of time and energy it took to collect this
// information, if you find new information we would appreciate if you made it
// freely available as well.
//
// JLH: Commented out MAME specific crap
#include "ay8910.h"
#include <string.h> // for memset()
#define MAX_OUTPUT 0x7FFF
// See AY8910_set_clock() for definition of STEP
#define STEP 0x8000
struct AY8910
{
int Channel;
int SampleRate;
// mem_read_handler PortAread;
// mem_read_handler PortBread;
// mem_write_handler PortAwrite;
// mem_write_handler PortBwrite;
int register_latch;
unsigned char Regs[16];
int lastEnable;
unsigned int UpdateStep;
int PeriodA, PeriodB, PeriodC, PeriodN, PeriodE;
int CountA, CountB, CountC, CountN, CountE;
unsigned int VolA, VolB, VolC, VolE;
unsigned char EnvelopeA, EnvelopeB, EnvelopeC;
unsigned char OutputA, OutputB, OutputC, OutputN;
signed char CountEnv;
unsigned char Hold, Alternate, Attack, Holding;
int RNG;
unsigned int VolTable[32];
};
/* register id's */
#define AY_AFINE (0)
#define AY_ACOARSE (1)
#define AY_BFINE (2)
#define AY_BCOARSE (3)
#define AY_CFINE (4)
#define AY_CCOARSE (5)
#define AY_NOISEPER (6)
#define AY_ENABLE (7)
#define AY_AVOL (8)
#define AY_BVOL (9)
#define AY_CVOL (10)
#define AY_EFINE (11)
#define AY_ECOARSE (12)
#define AY_ESHAPE (13)
#define AY_PORTA (14)
#define AY_PORTB (15)
static struct AY8910 AYPSG[MAX_8910]; /* array of PSG's */
void _AYWriteReg(int n, int r, int v)
{
struct AY8910 *PSG = &AYPSG[n];
int old;
PSG->Regs[r] = v;
/* A note about the period of tones, noise and envelope: for speed reasons, *
* we count down from the period to 0, but careful studies of the chip *
* output prove that it instead counts up from 0 until the counter becomes *
* greater or equal to the period. This is an important difference when the *
* program is rapidly changing the period to modulate the sound. *
* To compensate for the difference, when the period is changed we adjust *
* our internal counter. *
* Also, note that period = 0 is the same as period = 1. This is mentioned *
* in the YM2203 data sheets. However, this does NOT apply to the Envelope *
* period. In that case, period = 0 is half as period = 1. */
switch (r)
{
case AY_AFINE:
case AY_ACOARSE:
PSG->Regs[AY_ACOARSE] &= 0x0F;
old = PSG->PeriodA;
PSG->PeriodA = (PSG->Regs[AY_AFINE] + 256 * PSG->Regs[AY_ACOARSE]) * PSG->UpdateStep;
if (PSG->PeriodA == 0)
PSG->PeriodA = PSG->UpdateStep;
PSG->CountA += PSG->PeriodA - old;
if (PSG->CountA <= 0)
PSG->CountA = 1;
break;
case AY_BFINE:
case AY_BCOARSE:
PSG->Regs[AY_BCOARSE] &= 0x0F;
old = PSG->PeriodB;
PSG->PeriodB = (PSG->Regs[AY_BFINE] + 256 * PSG->Regs[AY_BCOARSE]) * PSG->UpdateStep;
if (PSG->PeriodB == 0)
PSG->PeriodB = PSG->UpdateStep;
PSG->CountB += PSG->PeriodB - old;
if (PSG->CountB <= 0)
PSG->CountB = 1;
break;
case AY_CFINE:
case AY_CCOARSE:
PSG->Regs[AY_CCOARSE] &= 0x0F;
old = PSG->PeriodC;
PSG->PeriodC = (PSG->Regs[AY_CFINE] + 256 * PSG->Regs[AY_CCOARSE]) * PSG->UpdateStep;
if (PSG->PeriodC == 0)
PSG->PeriodC = PSG->UpdateStep;
PSG->CountC += PSG->PeriodC - old;
if (PSG->CountC <= 0)
PSG->CountC = 1;
break;
case AY_NOISEPER:
PSG->Regs[AY_NOISEPER] &= 0x1F;
old = PSG->PeriodN;
PSG->PeriodN = PSG->Regs[AY_NOISEPER] * PSG->UpdateStep;
if (PSG->PeriodN == 0)
PSG->PeriodN = PSG->UpdateStep;
PSG->CountN += PSG->PeriodN - old;
if (PSG->CountN <= 0)
PSG->CountN = 1;
break;
case AY_ENABLE:
if ((PSG->lastEnable == -1) ||
((PSG->lastEnable & 0x40) != (PSG->Regs[AY_ENABLE] & 0x40)))
{
/* write out 0xff if port set to input */
// if (PSG->PortAwrite)
// (*PSG->PortAwrite)(0, (UINT8) ((PSG->Regs[AY_ENABLE] & 0x40) ? PSG->Regs[AY_PORTA] : 0xff)); // [TC: UINT8 cast]
}
if ((PSG->lastEnable == -1) ||
((PSG->lastEnable & 0x80) != (PSG->Regs[AY_ENABLE] & 0x80)))
{
/* write out 0xff if port set to input */
// if (PSG->PortBwrite)
// (*PSG->PortBwrite)(0, (UINT8) ((PSG->Regs[AY_ENABLE] & 0x80) ? PSG->Regs[AY_PORTB] : 0xff)); // [TC: UINT8 cast]
}
PSG->lastEnable = PSG->Regs[AY_ENABLE];
break;
case AY_AVOL:
PSG->Regs[AY_AVOL] &= 0x1F;
PSG->EnvelopeA = PSG->Regs[AY_AVOL] & 0x10;
PSG->VolA = PSG->EnvelopeA ? PSG->VolE : PSG->VolTable[PSG->Regs[AY_AVOL] ? PSG->Regs[AY_AVOL]*2+1 : 0];
break;
case AY_BVOL:
PSG->Regs[AY_BVOL] &= 0x1F;
PSG->EnvelopeB = PSG->Regs[AY_BVOL] & 0x10;
PSG->VolB = PSG->EnvelopeB ? PSG->VolE : PSG->VolTable[PSG->Regs[AY_BVOL] ? PSG->Regs[AY_BVOL]*2+1 : 0];
break;
case AY_CVOL:
PSG->Regs[AY_CVOL] &= 0x1F;
PSG->EnvelopeC = PSG->Regs[AY_CVOL] & 0x10;
PSG->VolC = PSG->EnvelopeC ? PSG->VolE : PSG->VolTable[PSG->Regs[AY_CVOL] ? PSG->Regs[AY_CVOL]*2+1 : 0];
break;
case AY_EFINE:
case AY_ECOARSE:
old = PSG->PeriodE;
PSG->PeriodE = ((PSG->Regs[AY_EFINE] + 256 * PSG->Regs[AY_ECOARSE])) * PSG->UpdateStep;
if (PSG->PeriodE == 0)
PSG->PeriodE = PSG->UpdateStep / 2;
PSG->CountE += PSG->PeriodE - old;
if (PSG->CountE <= 0)
PSG->CountE = 1;
break;
case AY_ESHAPE:
/* envelope shapes:
C AtAlH
0 0 x x \___
0 1 x x /___
1 0 0 0 \\\\
1 0 0 1 \___
1 0 1 0 \/\/
___
1 0 1 1 \
1 1 0 0 ////
___
1 1 0 1 /
1 1 1 0 /\/\
1 1 1 1 /___
The envelope counter on the AY-3-8910 has 16 steps. On the YM2149 it
has twice the steps, happening twice as fast. Since the end result is
just a smoother curve, we always use the YM2149 behaviour.
*/
PSG->Regs[AY_ESHAPE] &= 0x0F;
PSG->Attack = (PSG->Regs[AY_ESHAPE] & 0x04) ? 0x1F : 0x00;
if ((PSG->Regs[AY_ESHAPE] & 0x08) == 0)
{
/* if Continue = 0, map the shape to the equivalent one which has Continue = 1 */
PSG->Hold = 1;
PSG->Alternate = PSG->Attack;
}
else
{
PSG->Hold = PSG->Regs[AY_ESHAPE] & 0x01;
PSG->Alternate = PSG->Regs[AY_ESHAPE] & 0x02;
}
PSG->CountE = PSG->PeriodE;
PSG->CountEnv = 0x1F;
PSG->Holding = 0;
PSG->VolE = PSG->VolTable[PSG->CountEnv ^ PSG->Attack];
if (PSG->EnvelopeA)
PSG->VolA = PSG->VolE;
if (PSG->EnvelopeB)
PSG->VolB = PSG->VolE;
if (PSG->EnvelopeC)
PSG->VolC = PSG->VolE;
break;
case AY_PORTA:
if (PSG->Regs[AY_ENABLE] & 0x40)
{
// if (PSG->PortAwrite)
// (*PSG->PortAwrite)(0, PSG->Regs[AY_PORTA]);
// else
// logerror("PC %04x: warning - write %02x to 8910 #%d Port A\n",activecpu_get_pc(),PSG->Regs[AY_PORTA],n);
}
else
{
// logerror("warning: write to 8910 #%d Port A set as input - ignored\n",n);
}
break;
case AY_PORTB:
if (PSG->Regs[AY_ENABLE] & 0x80)
{
// if (PSG->PortBwrite)
// (*PSG->PortBwrite)(0, PSG->Regs[AY_PORTB]);
// else
// logerror("PC %04x: warning - write %02x to 8910 #%d Port B\n",activecpu_get_pc(),PSG->Regs[AY_PORTB],n);
}
else
{
// logerror("warning: write to 8910 #%d Port B set as input - ignored\n",n);
}
break;
}
}
// /length/ is the number of samples we require
// NB. This should be called at twice the 6522 IRQ rate or (eg) 60Hz if no IRQ.
void AY8910Update(int chip, int16_t ** buffer, int length) // [TC: Removed static]
{
struct AY8910 * PSG = &AYPSG[chip];
int16_t * buf1, * buf2, * buf3;
int outn;
buf1 = buffer[0];
buf2 = buffer[1];
buf3 = buffer[2];
/* The 8910 has three outputs, each output is the mix of one of the three *
* tone generators and of the (single) noise generator. The two are mixed *
* BEFORE going into the DAC. The formula to mix each channel is: *
* (ToneOn | ToneDisable) & (NoiseOn | NoiseDisable). *
* Note that this means that if both tone and noise are disabled, the output *
* is 1, not 0, and can be modulated changing the volume. *
* *
* If the channels are disabled, set their output to 1, and increase the *
* counter, if necessary, so they will not be inverted during this update. *
* Setting the output to 1 is necessary because a disabled channel is locked *
* into the ON state (see above); and it has no effect if the volume is 0. *
* If the volume is 0, increase the counter, but don't touch the output. */
if (PSG->Regs[AY_ENABLE] & 0x01)
{
if (PSG->CountA <= length * STEP)
PSG->CountA += length * STEP;
PSG->OutputA = 1;
}
else if (PSG->Regs[AY_AVOL] == 0)
{
/* note that I do count += length, NOT count = length + 1. You might think *
* it's the same since the volume is 0, but doing the latter could cause *
* interferencies when the program is rapidly modulating the volume. */
if (PSG->CountA <= length * STEP)
PSG->CountA += length * STEP;
}
if (PSG->Regs[AY_ENABLE] & 0x02)
{
if (PSG->CountB <= length * STEP)
PSG->CountB += length * STEP;
PSG->OutputB = 1;
}
else if (PSG->Regs[AY_BVOL] == 0)
{
if (PSG->CountB <= length * STEP)
PSG->CountB += length * STEP;
}
if (PSG->Regs[AY_ENABLE] & 0x04)
{
if (PSG->CountC <= length * STEP)
PSG->CountC += length * STEP;
PSG->OutputC = 1;
}
else if (PSG->Regs[AY_CVOL] == 0)
{
if (PSG->CountC <= length * STEP)
PSG->CountC += length * STEP;
}
/* for the noise channel we must not touch OutputN - it's also not necessary *
* since we use outn. */
if ((PSG->Regs[AY_ENABLE] & 0x38) == 0x38) /* all off */
if (PSG->CountN <= length * STEP)
PSG->CountN += length * STEP;
outn = (PSG->OutputN | PSG->Regs[AY_ENABLE]);
/* buffering loop */
while (length)
{
int vola, volb, volc;
int left;
/* vola, volb and volc keep track of how long each square wave stays *
* in the 1 position during the sample period. */
vola = volb = volc = 0;
left = STEP;
do
{
int nextevent;
if (PSG->CountN < left)
nextevent = PSG->CountN;
else
nextevent = left;
if (outn & 0x08)
{
if (PSG->OutputA)
vola += PSG->CountA;
PSG->CountA -= nextevent;
/* PeriodA is the half period of the square wave. Here, in each *
* loop I add PeriodA twice, so that at the end of the loop the *
* square wave is in the same status (0 or 1) it was at the start. *
* vola is also incremented by PeriodA, since the wave has been 1 *
* exactly half of the time, regardless of the initial position. *
* If we exit the loop in the middle, OutputA has to be inverted *
* and vola incremented only if the exit status of the square *
* wave is 1. */
while (PSG->CountA <= 0)
{
PSG->CountA += PSG->PeriodA;
if (PSG->CountA > 0)
{
PSG->OutputA ^= 1;
if (PSG->OutputA)
vola += PSG->PeriodA;
break;
}
PSG->CountA += PSG->PeriodA;
vola += PSG->PeriodA;
}
if (PSG->OutputA)
vola -= PSG->CountA;
}
else
{
PSG->CountA -= nextevent;
while (PSG->CountA <= 0)
{
PSG->CountA += PSG->PeriodA;
if (PSG->CountA > 0)
{
PSG->OutputA ^= 1;
break;
}
PSG->CountA += PSG->PeriodA;
}
}
if (outn & 0x10)
{
if (PSG->OutputB)
volb += PSG->CountB;
PSG->CountB -= nextevent;
while (PSG->CountB <= 0)
{
PSG->CountB += PSG->PeriodB;
if (PSG->CountB > 0)
{
PSG->OutputB ^= 1;
if (PSG->OutputB)
volb += PSG->PeriodB;
break;
}
PSG->CountB += PSG->PeriodB;
volb += PSG->PeriodB;
}
if (PSG->OutputB)
volb -= PSG->CountB;
}
else
{
PSG->CountB -= nextevent;
while (PSG->CountB <= 0)
{
PSG->CountB += PSG->PeriodB;
if (PSG->CountB > 0)
{
PSG->OutputB ^= 1;
break;
}
PSG->CountB += PSG->PeriodB;
}
}
if (outn & 0x20)
{
if (PSG->OutputC)
volc += PSG->CountC;
PSG->CountC -= nextevent;
while (PSG->CountC <= 0)
{
PSG->CountC += PSG->PeriodC;
if (PSG->CountC > 0)
{
PSG->OutputC ^= 1;
if (PSG->OutputC)
volc += PSG->PeriodC;
break;
}
PSG->CountC += PSG->PeriodC;
volc += PSG->PeriodC;
}
if (PSG->OutputC)
volc -= PSG->CountC;
}
else
{
PSG->CountC -= nextevent;
while (PSG->CountC <= 0)
{
PSG->CountC += PSG->PeriodC;
if (PSG->CountC > 0)
{
PSG->OutputC ^= 1;
break;
}
PSG->CountC += PSG->PeriodC;
}
}
PSG->CountN -= nextevent;
if (PSG->CountN <= 0)
{
/* Is noise output going to change? */
if ((PSG->RNG + 1) & 0x00002) /* (bit0^bit1)? */
{
PSG->OutputN = ~PSG->OutputN;
outn = (PSG->OutputN | PSG->Regs[AY_ENABLE]);
}
/* The Random Number Generator of the 8910 is a 17-bit shift *
* register. The input to the shift register is bit0 XOR bit3 *
* (bit0 is the output). This was verified on AY-3-8910 and *
* YM2149 chips. *
* *
* The following is a fast way to compute bit17 = bit0^bit3. *
* Instead of doing all the logic operations, we only check *
* bit0, relying on the fact that after three shifts of the *
* register, what now is bit3 will become bit0, and will *
* invert, if necessary, bit14, which previously was bit17. */
if (PSG->RNG & 0x00001)
PSG->RNG ^= 0x24000; /* This version is called the "Galois configuration". */
PSG->RNG >>= 1;
PSG->CountN += PSG->PeriodN;
}
left -= nextevent;
}
while (left > 0);
/* update envelope */
if (PSG->Holding == 0)
{
PSG->CountE -= STEP;
if (PSG->CountE <= 0)
{
do
{
PSG->CountEnv--;
PSG->CountE += PSG->PeriodE;
}
while (PSG->CountE <= 0);
/* check envelope current position */
if (PSG->CountEnv < 0)
{
if (PSG->Hold)
{
if (PSG->Alternate)
PSG->Attack ^= 0x1F;
PSG->Holding = 1;
PSG->CountEnv = 0;
}
else
{
/* if CountEnv has looped an odd number of times (usually 1), *
* invert the output. */
if (PSG->Alternate && (PSG->CountEnv & 0x20))
PSG->Attack ^= 0x1F;
PSG->CountEnv &= 0x1F;
}
}
PSG->VolE = PSG->VolTable[PSG->CountEnv ^ PSG->Attack];
/* reload volume */
if (PSG->EnvelopeA)
PSG->VolA = PSG->VolE;
if (PSG->EnvelopeB)
PSG->VolB = PSG->VolE;
if (PSG->EnvelopeC)
PSG->VolC = PSG->VolE;
}
}
#if 0
*(buf1++) = (vola * PSG->VolA) / STEP;
*(buf2++) = (volb * PSG->VolB) / STEP;
*(buf3++) = (volc * PSG->VolC) / STEP;
#else // [Tom's code...]
// Output PCM wave [-32768...32767] instead of MAME's voltage level [0...32767]
// - This allows for better s/w mixing
if (PSG->VolA)
{
if (vola)
*(buf1++) = (vola * PSG->VolA) / STEP;
else
*(buf1++) = -(int)PSG->VolA;
}
else
*(buf1++) = 0;
if (PSG->VolB)
{
if (volb)
*(buf2++) = (volb * PSG->VolB) / STEP;
else
*(buf2++) = -(int)PSG->VolB;
}
else
*(buf2++) = 0;
if (PSG->VolC)
{
if (volc)
*(buf3++) = (volc * PSG->VolC) / STEP;
else
*(buf3++) = -(int)PSG->VolC;
}
else
*(buf3++) = 0;
#endif
length--;
}
}
static void AY8910_set_clock(int chip, int clock)
{
struct AY8910 * PSG = &AYPSG[chip];
/* The step clock for the tone and noise generators is the chip clock *
* divided by 8; for the envelope generator of the AY-3-8910, it is half *
* that much (clock/16), but the envelope of the YM2149 goes twice as *
* fast, therefore again clock/8. *
* Here we calculate the number of steps which happen during one sample *
* at the given sample rate. No. of events = sample rate / (clock/8). *
* STEP is a multiplier used to turn the fraction into a fixed point *
* number. */
PSG->UpdateStep = (unsigned int)(((double)STEP * PSG->SampleRate * 8 + clock / 2) / clock); // [TC: unsigned int cast]
}
static void build_mixer_table(int chip)
{
struct AY8910 * PSG = &AYPSG[chip];
/* calculate the volume->voltage conversion table */
/* The AY-3-8910 has 16 levels, in a logarithmic scale (3dB per step) */
/* The YM2149 still has 16 levels for the tone generators, but 32 for */
/* the envelope generator (1.5dB per step). */
double out = MAX_OUTPUT;
for(int i=31; i>0; i--)
{
PSG->VolTable[i] = (unsigned int)(out + 0.5); /* round to nearest */ // [TC: unsigned int cast]
out /= 1.188502227; /* = 10 ^ (1.5/20) = 1.5dB */
}
PSG->VolTable[0] = 0;
}
void AY8910_reset(int chip)
{
int i;
struct AY8910 * PSG = &AYPSG[chip];
PSG->register_latch = 0;
PSG->RNG = 1;
PSG->OutputA = 0;
PSG->OutputB = 0;
PSG->OutputC = 0;
PSG->OutputN = 0xFF;
PSG->lastEnable = -1; /* force a write */
for(i=0; i<AY_PORTA; i++)
_AYWriteReg(chip, i, 0); /* AYWriteReg() uses the timer system; we cannot */
/* call it at this time because the timer system */
/* has not been initialized. */
}
// This stuff looks like Tom's code, so let's streamline and un-MSHungarianize this shit:
// [DONE]
void AY8910_InitAll(int clock, int sampleRate)
{
for(int chip=0; chip<MAX_8910; chip++)
{
struct AY8910 * PSG = &AYPSG[chip];
memset(PSG, 0, sizeof(struct AY8910));
PSG->SampleRate = sampleRate;
AY8910_set_clock(chip, clock);
build_mixer_table(chip);
}
}
void AY8910_InitClock(int clock)
{
for(int chip=0; chip<MAX_8910; chip++)
AY8910_set_clock(chip, clock);
}
uint8_t * AY8910_GetRegsPtr(uint16_t chipNum)
{
if (chipNum >= MAX_8910)
return NULL;
return &AYPSG[chipNum].Regs[0];
}
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