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working on noise

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This commit is contained in:
Jorj Bauer 2017-03-03 15:34:12 -05:00
parent b8e23bfa22
commit 8c7a97ee54
2 changed files with 54 additions and 15 deletions
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67
apple/ay8910.cpp
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@ -62,6 +62,26 @@ void AY8910::Reset()
envDirection = 1;
noiseFlipTimer = 0;
noiseFlag = true;
lcgBitsRemaining = 0;
#if 0
// Debugging
r[ENV_PERIOD_COARSE] = 0xFF;
r[ENV_PERIOD_FINE] = 0xFF;
envelopeTimer = 1;
envelopeTime = calculateEnvelopeTime();
r[ENV_SHAPE] = 0x08; // sawtooth, descending
if (r[ENV_SHAPE] & AY_ENV_ATTACK) {
// rising
envDirection = 1;
envCounter = 0;
} else {
// falling
envDirection = -1;
envCounter = 15;
}
#endif
}
uint8_t AY8910::read(uint8_t reg)
@ -134,7 +154,15 @@ void AY8910::write(uint8_t reg, uint8_t PortA)
envelopeTime = calculateEnvelopeTime();
envelopeTimer = 0; // reset so it will pick up @ next tick
} else if (curRegister == ENV_SHAPE) {
envDirection = (r[ENV_SHAPE] & AY_ENV_ATTACK) ? 1 : -1;
if (r[ENV_SHAPE] & AY_ENV_ATTACK) {
// rising
envDirection = 1;
envCounter = 0;
} else {
// falling
envDirection = -1;
envCounter = 15;
}
} else if (curRegister == NOISE_PERIOD) {
noiseFlipTimer = g_cpu->cycles + cycleTimeForNoise();
}
@ -176,18 +204,19 @@ uint16_t AY8910::cycleTimeForNoise()
uint8_t regval = r[NOISE_PERIOD];
if (regval == 0) regval++;
return (16 * regval) / 4;
return (512 * regval) / 4;
}
// Similar calculation: this one, for the envelope timer.
// FIXME: I *think* this is right. Not sure. Needs validation.
uint32_t AY8910::calculateEnvelopeTime()
{
uint16_t regVal = (r[0x0C] << 8) | (r[0x0B]);
uint32_t regVal = (r[ENV_PERIOD_COARSE] << 8) | (r[ENV_PERIOD_FINE]);
if (regVal == 0) regVal++;
return (512 * regVal) / 4;
// This constant is wrong by about 2%. But it should be fast b/c
// powers of 2.
return (32 * regVal) / 4;
}
void AY8910::update(uint32_t cpuCycleCount)
@ -247,8 +276,8 @@ void AY8910::update(uint32_t cpuCycleCount)
}
break;
case 0x80:
case 0xC0:
case 0x08:
case 0x0C:
// These two jump back to the start when they get to the end.
if (envCounter > 15) {
@ -258,8 +287,8 @@ void AY8910::update(uint32_t cpuCycleCount)
}
break;
case 0xA0:
case 0xE0:
case 0x0A:
case 0x0E:
break;
// These two reverse direction.
if (envCounter == 15 || envCounter == 0) {
@ -277,14 +306,22 @@ void AY8910::update(uint32_t cpuCycleCount)
// For the noise timer: if it expires, we get another random bit
if (noiseFlipTimer && noiseFlipTimer <= cpuCycleCount) {
// FIXME: srnd() this somewhere when we initialized? Does it matter?
uint8_t rnd = lcg.rnd();
// Use the higher bits of the RNG; the low bits have low periodicity.
// FIXME: is this sophisticated enough? Does it get the noise
// profile we want? Should we ^ with some other bit to get a
// different period profile?
noiseFlag = (rnd & 0x80);
if (!lcgBitsRemaining) {
lcgBitsRemaining = 8;
lcgLastByte = lcg.rnd();
}
noiseFlag = lcgLastByte & 1;
lcgLastByte >>= 1;
lcgBitsRemaining--;
}
#if 0
// DEBUGGING ENVELOPES: just output the envelope
g_speaker->mixOutput(volumeLevels[envCounter]);
return;
#endif
// For any waveformFlipTimer that is > 0: if cpuCycleCount is larger
// than the timer, we'll flip state. (It's a square wave!)

2
apple/ay8910.h
View File

@ -71,6 +71,8 @@ class AY8910 {
bool noiseFlag;
LCG lcg;
uint8_t lcgLastByte;
uint8_t lcgBitsRemaining;
};
#endif