ref: 88b781094d31f244b52a420330ec8049d7ca7b36
dir: /src/pt2_paula.c/
/* Simple Paula emulator by 8bitbubsy (with BLEP synthesis by aciddose).
** Limitation: The audio output frequency can't be below 31389Hz ( ceil(PAULA_PAL_CLK / 113.0) )
**
** WARNING: These functions must not be called while paulaGenerateSamples() is running!
** If so, lock the audio first so that you're sure it's not running.
*/
#include <stdint.h>
#include <stdbool.h>
#include "pt2_paula.h"
#include "pt2_blep.h"
#include "pt2_rcfilter.h"
#include "pt2_ledfilter.h"
#include "pt2_math.h"
typedef struct voice_t
{
volatile bool DMA_active;
// internal registers
bool DMATriggerFlag, nextSampleStage;
int8_t AUD_DAT[2]; // DMA data buffer
const int8_t *location; // current location
uint16_t lengthCounter; // current length
int32_t sampleCounter; // how many bytes left in AUD_DAT
double dSample; // currently held sample point (multiplied by volume)
double dDelta, dPhase;
// for BLEP synthesis
double dLastDelta, dLastPhase, dLastDeltaMul, dBlepOffset, dDeltaMul;
// registers modified by Paula functions
const int8_t *AUD_LC; // location (data pointer)
uint16_t AUD_LEN;
double AUD_PER_delta, AUD_PER_deltamul;
double AUD_VOL;
} paulaVoice_t;
static bool useLEDFilter, useLowpassFilter, useHighpassFilter;
static int8_t nullSample[0xFFFF*2]; // buffer for NULL data pointer
static double dPaulaOutputFreq, dPeriodToDeltaDiv;
static blep_t blep[PAULA_VOICES];
static rcFilter_t filterLo, filterHi;
static ledFilter_t filterLED;
static paulaVoice_t paula[PAULA_VOICES];
void paulaSetup(double dOutputFreq, uint32_t amigaModel)
{
if (dOutputFreq <= 0.0)
dOutputFreq = 44100.0;
dPaulaOutputFreq = dOutputFreq;
dPeriodToDeltaDiv = PAULA_PAL_CLK / dPaulaOutputFreq;
useLowpassFilter = useHighpassFilter = true;
clearRCFilterState(&filterLo);
clearRCFilterState(&filterHi);
clearLEDFilterState(&filterLED);
/* Amiga 500/1200 filter emulation
**
** aciddose:
** First comes a static low-pass 6dB formed by the supply current
** from the Paula's mixture of channels A+B / C+D into the opamp with
** 0.1uF capacitor and 360 ohm resistor feedback in inverting mode biased by
** dac vRef (used to center the output).
**
** R = 360 ohm
** C = 0.1uF
** Low Hz = 4420.97~ = 1 / (2pi * 360 * 0.0000001)
**
** Under spice simulation the circuit yields -3dB = 4400Hz.
**
** Next comes a bog-standard Sallen-Key filter ("LED") with:
** R1 = 10K ohm
** R2 = 10K ohm
** C1 = 6800pF
** C2 = 3900pF
** Q = 0.660 (8bitbubsy: edited with correct nominal)
**
** This filter is optionally bypassed by an MPF-102 JFET chip when
** the LED filter is turned off.
**
** Under spice simulation the circuit yields -3dB = 2800Hz.
** 90 degrees phase = 3000Hz (so, should oscillate at 3kHz!)
**
** The buffered output of the Sallen-Key passes into an RC high-pass with:
** R = 1.39K ohm (1K ohm + 390 ohm)
** C = 22uF (also C = 330nF, for improved high-frequency)
**
** High Hz = 5.2~ = 1 / (2pi * 1390 * 0.000022)
** Under spice simulation the circuit yields -3dB = 5.2Hz.
**
** 8bitbubsy:
** Keep in mind that many of the Amiga schematics that are floating around on
** the internet have wrong RC values! They were most likely very early schematics
** that didn't change before production (or changes that never reached production).
** This has been confirmed by measuring the components on several Amiga motherboards.
**
** Correct values for A500, >rev3 (?) (A500_R6.pdf):
** - 1-pole RC 6dB/oct low-pass: R=360 ohm, C=0.1uF
** - Sallen-key low-pass ("LED"): R1/R2=10k ohm, C1=6800pF, C2=3900pF
** - 1-pole RC 6dB/oct high-pass: R=1390 ohm (1000+390), C=22.33uF (22+0.33)
**
** Correct values for A1200, all revs (A1200_R2.pdf):
** - 1-pole RC 6dB/oct low-pass: R=680 ohm, C=6800pF
** - Sallen-key low-pass ("LED"): R1/R2=10k ohm, C1=6800pF, C2=3900pF (same as A500)
** - 1-pole RC 6dB/oct high-pass: R=1360 ohm (1000+360), C=22uF
*/
double R, C, R1, R2, C1, C2, cutoff, qfactor;
if (amigaModel == MODEL_A500)
{
// A500 1-pole (6db/oct) static RC low-pass filter:
R = 360.0; // R321 (360 ohm)
C = 1e-7; // C321 (0.1uF)
cutoff = 1.0 / (PT2_TWO_PI * R * C); // ~4420.971Hz
calcRCFilterCoeffs(dPaulaOutputFreq, cutoff, &filterLo);
// A500 1-pole (6dB/oct) static RC high-pass filter:
R = 1390.0; // R324 (1K ohm) + R325 (390 ohm)
C = 2.233e-5; // C334 (22uF) + C335 (0.33uF)
cutoff = 1.0 / (PT2_TWO_PI * R * C); // ~5.128Hz
calcRCFilterCoeffs(dPaulaOutputFreq, cutoff, &filterHi);
}
else
{
/* Don't use the A1200 low-pass filter since its cutoff
** is well above human hearable range anyway (~34.4kHz).
** We don't do volume PWM, so we have nothing we need to
** filter away.
*/
useLowpassFilter = false;
// A1200 1-pole (6dB/oct) static RC high-pass filter:
R = 1360.0; // R324 (1K ohm resistor) + R325 (360 ohm resistor)
C = 2.2e-5; // C334 (22uF capacitor)
cutoff = 1.0 / (PT2_TWO_PI * R * C); // ~5.319Hz
calcRCFilterCoeffs(dPaulaOutputFreq, cutoff, &filterHi);
}
// Sallen-Key low-pass filter ("LED" filter, same values on A500/A1200):
R1 = 10000.0; // R322 (10K ohm)
R2 = 10000.0; // R323 (10K ohm)
C1 = 6.8e-9; // C322 (6800pF)
C2 = 3.9e-9; // C323 (3900pF)
cutoff = 1.0 / (PT2_TWO_PI * pt2_sqrt(R1 * R2 * C1 * C2)); // ~3090.533Hz
qfactor = pt2_sqrt(R1 * R2 * C1 * C2) / (C2 * (R1 + R2)); // ~0.660225
calcLEDFilterCoeffs(dPaulaOutputFreq, cutoff, qfactor, &filterLED);
}
void paulaDisableFilters(void) // disables low-pass/high-pass filter ("LED" filter is kept)
{
useHighpassFilter = false;
useLowpassFilter = false;
}
int8_t *paulaGetNullSamplePtr(void)
{
return nullSample;
}
static void audxper(int32_t ch, uint16_t period)
{
paulaVoice_t *v = &paula[ch];
int32_t realPeriod = period;
if (realPeriod == 0)
realPeriod = 65536; // On Amiga: period 0 = period 65536 (1+65535)
else if (realPeriod < 113)
realPeriod = 113; // close to what happens on real Amiga (and low-limit needed for BLEP synthesis)
// to be read on next sampling step (or on DMA trigger)
v->AUD_PER_delta = dPeriodToDeltaDiv / realPeriod;
v->AUD_PER_deltamul = 1.0 / v->AUD_PER_delta; // for BLEP synthesis (prevents division in inner mixing loop)
// handle BLEP synthesis edge-cases
if (v->dLastDelta == 0.0)
v->dLastDelta = v->AUD_PER_delta;
if (v->dLastDeltaMul == 0.0)
v->dLastDeltaMul = v->AUD_PER_deltamul;
}
static void audxvol(int32_t ch, uint16_t vol)
{
int32_t realVol = vol & 127;
if (realVol > 64)
realVol = 64;
// multiplying sample point by this also scales the sample from -128..127 -> -1.000 .. ~0.992
paula[ch].AUD_VOL = realVol * (1.0 / (128.0 * 64.0));
}
static void audxlen(int32_t ch, uint16_t len)
{
paula[ch].AUD_LEN = len;
}
static void audxdat(int32_t ch, const int8_t *src)
{
if (src == NULL)
src = nullSample;
paula[ch].AUD_LC = src;
}
static inline void refetchPeriod(paulaVoice_t *v) // Paula stage
{
// set BLEP stuff
v->dLastPhase = v->dPhase;
v->dLastDelta = v->dDelta;
v->dLastDeltaMul = v->dDeltaMul;
v->dBlepOffset = v->dLastPhase * v->dLastDeltaMul;
// Paula only updates period (delta) during period refetching (this stage)
v->dDelta = v->AUD_PER_delta;
v->dDeltaMul = v->AUD_PER_deltamul;
v->nextSampleStage = true;
}
static void startDMA(int32_t ch)
{
paulaVoice_t *v = &paula[ch];
if (v->AUD_LC == NULL)
v->AUD_LC = nullSample;
// immediately update AUD_LC/AUD_LEN
v->location = v->AUD_LC;
v->lengthCounter = v->AUD_LEN;
// make Paula fetch new samples immediately
v->sampleCounter = 0;
v->DMATriggerFlag = true;
refetchPeriod(v);
v->dPhase = 0.0; // kludge: must be cleared *after* refetchPeriod()
v->DMA_active = true;
}
static void stopDMA(int32_t ch)
{
paula[ch].DMA_active = false;
}
void paulaWriteByte(uint32_t address, uint16_t data8)
{
if (address == 0)
return;
switch (address)
{
// CIA-A ("LED" filter control only)
case 0xBFE001:
{
const bool oldLedFilterState = useLEDFilter;
useLEDFilter = !!(data8 & 2);
if (useLEDFilter != oldLedFilterState)
clearLEDFilterState(&filterLED);
}
break;
// AUDxVOL ( byte-write to AUDxVOL works on most Amigas (not 68040/68060) )
case 0xDFF0A8: audxvol(0, data8); break;
case 0xDFF0B8: audxvol(1, data8); break;
case 0xDFF0C8: audxvol(2, data8); break;
case 0xDFF0D8: audxvol(3, data8); break;
default: return;
}
}
void paulaWriteWord(uint32_t address, uint16_t data16)
{
if (address == 0)
return;
switch (address)
{
// DMACON
case 0xDFF096:
{
if (data16 & 0x8000)
{
// set
if (data16 & 1) startDMA(0);
if (data16 & 2) startDMA(1);
if (data16 & 4) startDMA(2);
if (data16 & 8) startDMA(3);
}
else
{
// clear
if (data16 & 1) stopDMA(0);
if (data16 & 2) stopDMA(1);
if (data16 & 4) stopDMA(2);
if (data16 & 8) stopDMA(3);
}
}
break;
// AUDxLEN
case 0xDFF0A4: audxlen(0, data16); break;
case 0xDFF0B4: audxlen(1, data16); break;
case 0xDFF0C4: audxlen(2, data16); break;
case 0xDFF0D4: audxlen(3, data16); break;
// AUDxPER
case 0xDFF0A6: audxper(0, data16); break;
case 0xDFF0B6: audxper(1, data16); break;
case 0xDFF0C6: audxper(2, data16); break;
case 0xDFF0D6: audxper(3, data16); break;
// AUDxVOL
case 0xDFF0A8: audxvol(0, data16); break;
case 0xDFF0B8: audxvol(1, data16); break;
case 0xDFF0C8: audxvol(2, data16); break;
case 0xDFF0D8: audxvol(3, data16); break;
default: return;
}
}
void paulaWritePtr(uint32_t address, const int8_t *ptr)
{
if (address == 0)
return;
switch (address)
{
// AUDxDAT
case 0xDFF0A0: audxdat(0, ptr); break;
case 0xDFF0B0: audxdat(1, ptr); break;
case 0xDFF0C0: audxdat(2, ptr); break;
case 0xDFF0D0: audxdat(3, ptr); break;
default: return;
}
}
static inline void nextSample(paulaVoice_t *v, blep_t *b)
{
if (v->sampleCounter == 0)
{
// it's time to read new samples from DMA
// don't update AUD_LEN/AUD_LC yet on DMA trigger
if (!v->DMATriggerFlag)
{
if (--v->lengthCounter == 0)
{
v->lengthCounter = v->AUD_LEN;
v->location = v->AUD_LC;
}
}
v->DMATriggerFlag = false;
// fill DMA data buffer
v->AUD_DAT[0] = *v->location++;
v->AUD_DAT[1] = *v->location++;
v->sampleCounter = 2;
}
/* Pre-compute current sample point.
** Output volume is only read from AUDxVOL at this stage,
** and we don't emulate volume PWM anyway, so we can
** pre-multiply by volume here.
*/
v->dSample = v->AUD_DAT[0] * v->AUD_VOL; // -128..127 * 0.0 .. 1.0
// fill BLEP buffer if the new sample differs from the old one
if (v->dSample != b->dLastValue)
{
if (v->dLastDelta > v->dLastPhase)
blepAdd(b, v->dBlepOffset, b->dLastValue - v->dSample);
b->dLastValue = v->dSample;
}
// progress AUD_DAT buffer
v->AUD_DAT[0] = v->AUD_DAT[1];
v->sampleCounter--;
}
// output is -4.00 .. 3.97 (can be louder because of high-pass filter)
void paulaGenerateSamples(double *dOutL, double *dOutR, int32_t numSamples)
{
double *dMixBufSelect[PAULA_VOICES] = { dOutL, dOutR, dOutR, dOutL };
if (numSamples <= 0)
return;
// clear mix buffer block
memset(dOutL, 0, numSamples * sizeof (double));
memset(dOutR, 0, numSamples * sizeof (double));
// mix samples
paulaVoice_t *v = paula;
blep_t *b = blep;
for (int32_t i = 0; i < PAULA_VOICES; i++, v++, b++)
{
if (!v->DMA_active || v->location == NULL || v->AUD_LC == NULL)
continue;
double *dMixBuffer = dMixBufSelect[i]; // what output channel to mix into (L, R, R, L)
for (int32_t j = 0; j < numSamples; j++)
{
if (v->nextSampleStage)
{
v->nextSampleStage = false;
nextSample(v, b);
}
double dSample = v->dSample; // current sample, pre-multiplied by vol, scaled to -1.0 .. 0.992
if (b->samplesLeft > 0)
dSample = blepRun(b, dSample);
dMixBuffer[j] += dSample;
v->dPhase += v->dDelta;
if (v->dPhase >= 1.0)
{
v->dPhase -= 1.0;
refetchPeriod(v);
}
}
}
// apply Amiga filters
for (int32_t i = 0; i < numSamples; i++)
{
double dOut[2] = { dOutL[i], dOutR[i] };
if (useLowpassFilter)
RCLowPassFilterStereo(&filterLo, dOut, dOut);
if (useLEDFilter)
LEDFilter(&filterLED, dOut, dOut);
if (useHighpassFilter)
RCHighPassFilterStereo(&filterHi, dOut, dOut);
dOutL[i] = dOut[0];
dOutR[i] = dOut[1];
}
}