kopia lustrzana https://github.com/Jean-MarcHarvengt/MCUME
274 wiersze
6.3 KiB
C
274 wiersze
6.3 KiB
C
|
|
#include "shared.h"
|
|
|
|
#define MAX_OUTPUT 0x7fff
|
|
#define STEP 0x10000
|
|
#define FB_WNOISE 0x12000
|
|
#define FB_PNOISE 0x08000
|
|
#define NG_PRESET 0x0F35
|
|
|
|
struct SN76496
|
|
{
|
|
int SampleRate;
|
|
unsigned int UpdateStep;
|
|
int VolTable[16];
|
|
int Register[8];
|
|
int LastRegister;
|
|
int Volume[4];
|
|
unsigned int RNG;
|
|
int NoiseFB;
|
|
int Period[4];
|
|
int Count[4];
|
|
int Output[4];
|
|
};
|
|
|
|
|
|
struct SN76496 sn[MAX_76496];
|
|
|
|
|
|
|
|
void SN76496Write(int chip,int data)
|
|
{
|
|
struct SN76496 *R = &sn[chip];
|
|
|
|
if (data & 0x80)
|
|
{
|
|
int r = (data & 0x70) >> 4;
|
|
int c = r/2;
|
|
|
|
R->LastRegister = r;
|
|
R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
|
|
switch (r)
|
|
{
|
|
case 0: /* tone 0 : frequency */
|
|
case 2: /* tone 1 : frequency */
|
|
case 4: /* tone 2 : frequency */
|
|
R->Period[c] = R->UpdateStep * R->Register[r];
|
|
if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
|
|
if (r == 4)
|
|
{
|
|
/* update noise shift frequency */
|
|
if ((R->Register[6] & 0x03) == 0x03)
|
|
R->Period[3] = 2 * R->Period[2];
|
|
}
|
|
break;
|
|
case 1: /* tone 0 : volume */
|
|
case 3: /* tone 1 : volume */
|
|
case 5: /* tone 2 : volume */
|
|
case 7: /* noise : volume */
|
|
R->Volume[c] = R->VolTable[data & 0x0f];
|
|
break;
|
|
case 6: /* noise : frequency, mode */
|
|
{
|
|
int n = R->Register[6];
|
|
R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;
|
|
n &= 3;
|
|
/* N/512,N/1024,N/2048,Tone #3 output */
|
|
R->Period[3] = (n == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5+n));
|
|
|
|
/* reset noise shifter */
|
|
R->RNG = NG_PRESET;
|
|
R->Output[3] = R->RNG & 1;
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
int r = R->LastRegister;
|
|
int c = r/2;
|
|
|
|
switch (r)
|
|
{
|
|
case 0: /* tone 0 : frequency */
|
|
case 2: /* tone 1 : frequency */
|
|
case 4: /* tone 2 : frequency */
|
|
R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);
|
|
R->Period[c] = R->UpdateStep * R->Register[r];
|
|
if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
|
|
if (r == 4)
|
|
{
|
|
/* update noise shift frequency */
|
|
if ((R->Register[6] & 0x03) == 0x03)
|
|
R->Period[3] = 2 * R->Period[2];
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
void SN76496Update(int chip,signed short int *buffer,int length)
|
|
{
|
|
int i;
|
|
struct SN76496 *R = &sn[chip];
|
|
|
|
|
|
/* If the volume is 0, increase the counter */
|
|
for (i = 0;i < 4;i++)
|
|
{
|
|
if (R->Volume[i] == 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 (R->Count[i] <= length*STEP) R->Count[i] += length*STEP;
|
|
}
|
|
}
|
|
|
|
while (length > 0)
|
|
{
|
|
int vol[4];
|
|
unsigned int out;
|
|
int left;
|
|
|
|
|
|
/* vol[] keeps track of how long each square wave stays */
|
|
/* in the 1 position during the sample period. */
|
|
vol[0] = vol[1] = vol[2] = vol[3] = 0;
|
|
|
|
for (i = 0;i < 3;i++)
|
|
{
|
|
if (R->Output[i]) vol[i] += R->Count[i];
|
|
R->Count[i] -= STEP;
|
|
/* Period[i] is the half period of the square wave. Here, in each */
|
|
/* loop I add Period[i] 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. */
|
|
/* vol[i] is also incremented by Period[i], since the wave has been 1 */
|
|
/* exactly half of the time, regardless of the initial position. */
|
|
/* If we exit the loop in the middle, Output[i] has to be inverted */
|
|
/* and vol[i] incremented only if the exit status of the square */
|
|
/* wave is 1. */
|
|
while (R->Count[i] <= 0)
|
|
{
|
|
R->Count[i] += R->Period[i];
|
|
if (R->Count[i] > 0)
|
|
{
|
|
R->Output[i] ^= 1;
|
|
if (R->Output[i]) vol[i] += R->Period[i];
|
|
break;
|
|
}
|
|
R->Count[i] += R->Period[i];
|
|
vol[i] += R->Period[i];
|
|
}
|
|
if (R->Output[i]) vol[i] -= R->Count[i];
|
|
}
|
|
|
|
left = STEP;
|
|
do
|
|
{
|
|
int nextevent;
|
|
|
|
|
|
if (R->Count[3] < left) nextevent = R->Count[3];
|
|
else nextevent = left;
|
|
|
|
if (R->Output[3]) vol[3] += R->Count[3];
|
|
R->Count[3] -= nextevent;
|
|
if (R->Count[3] <= 0)
|
|
{
|
|
if (R->RNG & 1) R->RNG ^= R->NoiseFB;
|
|
R->RNG >>= 1;
|
|
R->Output[3] = R->RNG & 1;
|
|
R->Count[3] += R->Period[3];
|
|
if (R->Output[3]) vol[3] += R->Period[3];
|
|
}
|
|
if (R->Output[3]) vol[3] -= R->Count[3];
|
|
|
|
left -= nextevent;
|
|
} while (left > 0);
|
|
|
|
out = vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +
|
|
vol[2] * R->Volume[2] + vol[3] * R->Volume[3];
|
|
|
|
if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;
|
|
|
|
*(buffer++) = out / STEP;
|
|
|
|
length--;
|
|
}
|
|
}
|
|
|
|
|
|
|
|
void SN76496_set_clock(int chip,int clock)
|
|
{
|
|
struct SN76496 *R = &sn[chip];
|
|
|
|
|
|
/* the base clock for the tone generators is the chip clock divided by 16; */
|
|
/* for the noise generator, it is clock / 256. */
|
|
/* Here we calculate the number of steps which happen during one sample */
|
|
/* at the given sample rate. No. of events = sample rate / (clock/16). */
|
|
/* STEP is a multiplier used to turn the fraction into a fixed point */
|
|
/* number. */
|
|
R->UpdateStep = ((double)STEP * R->SampleRate * 16) / clock;
|
|
}
|
|
|
|
|
|
|
|
void SN76496_set_gain(int chip,int gain)
|
|
{
|
|
struct SN76496 *R = &sn[chip];
|
|
int i;
|
|
double out;
|
|
|
|
|
|
gain &= 0xff;
|
|
|
|
/* increase max output basing on gain (0.2 dB per step) */
|
|
out = MAX_OUTPUT / 3;
|
|
while (gain-- > 0)
|
|
out *= 1.023292992; /* = (10 ^ (0.2/20)) */
|
|
|
|
/* build volume table (2dB per step) */
|
|
for (i = 0;i < 15;i++)
|
|
{
|
|
/* limit volume to avoid clipping */
|
|
if (out > MAX_OUTPUT / 3) R->VolTable[i] = MAX_OUTPUT / 3;
|
|
else R->VolTable[i] = out;
|
|
|
|
out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */
|
|
}
|
|
R->VolTable[15] = 0;
|
|
}
|
|
|
|
|
|
|
|
int SN76496_init(int chip,int clock,int volume,int sample_rate)
|
|
{
|
|
int i;
|
|
struct SN76496 *R = &sn[chip];
|
|
|
|
R->SampleRate = sample_rate;
|
|
SN76496_set_clock(chip,clock);
|
|
|
|
for (i = 0;i < 4;i++) R->Volume[i] = 0;
|
|
|
|
R->LastRegister = 0;
|
|
for (i = 0;i < 8;i+=2)
|
|
{
|
|
R->Register[i] = 0;
|
|
R->Register[i + 1] = 0x0f; /* volume = 0 */
|
|
}
|
|
|
|
for (i = 0;i < 4;i++)
|
|
{
|
|
R->Output[i] = 0;
|
|
R->Period[i] = R->Count[i] = R->UpdateStep;
|
|
}
|
|
R->RNG = NG_PRESET;
|
|
R->Output[3] = R->RNG & 1;
|
|
|
|
return 0;
|
|
}
|
|
|
|
|
|
|
|
int SN76496_sh_start(int clock, int volume, int rate)
|
|
{
|
|
SN76496_init(0, clock, volume & 0xff, rate);
|
|
SN76496_set_gain(0, (volume >> 8) & 0xff);
|
|
return 0;
|
|
}
|