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AY8930: implement noise and/or mask 

cannot confirm whether this behavior is accurate to hardware though...
thanks Eulous for details on this!
This commit is contained in:
tildearrow 2022-01-18 18:21:27 -05:00
parent 488bd45907
commit 5a7cf57aa2
6 changed files with 68 additions and 24 deletions
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2
src/engine/dispatch.h
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@ -64,6 +64,8 @@ enum DivDispatchCmds {
DIV_CMD_AY_ENVELOPE_LOW,
DIV_CMD_AY_ENVELOPE_HIGH,
DIV_CMD_AY_ENVELOPE_SLIDE,
DIV_CMD_AY_NOISE_MASK_AND,
DIV_CMD_AY_NOISE_MASK_OR,
DIV_CMD_SAA_ENVELOPE,

18
src/engine/platform/ay8930.cpp
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@ -271,6 +271,14 @@ int DivPlatformAY8930::dispatch(DivCommand c) {
case DIV_CMD_AY_ENVELOPE_SLIDE:
ayEnvSlide[c.chan]=c.value;
break;
case DIV_CMD_AY_NOISE_MASK_AND:
ayNoiseAnd=c.value;
immWrite(0x19,ayNoiseAnd);
break;
case DIV_CMD_AY_NOISE_MASK_OR:
ayNoiseOr=c.value;
immWrite(0x1a,ayNoiseOr);
break;
case DIV_ALWAYS_SET_VOLUME:
return 0;
break;
@ -325,14 +333,8 @@ void DivPlatformAY8930::reset() {
pendingWrites[i]=-1;
}
lastBusy=60;
dacMode=0;
dacPeriod=0;
dacPos=0;
dacRate=0;
dacSample=-1;
sampleBank=0;
ayNoiseAnd=0;
ayNoiseOr=0;
delay=0;
extMode=false;

9
src/engine/platform/ay8930.h
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@ -28,14 +28,7 @@ class DivPlatformAY8930: public DivDispatch {
};
std::queue<QueuedWrite> writes;
ay8930_device* ay;
unsigned char lastBusy;
bool dacMode;
int dacPeriod;
int dacRate;
int dacPos;
int dacSample;
unsigned char sampleBank;
unsigned char ayNoiseAnd, ayNoiseOr;
bool bank;
int delay;

51
src/engine/platform/sound/ay8910.cpp
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@ -581,6 +581,8 @@ YM2203 English datasheet: http://www.appleii-box.de/APPLE2/JonasCard/YM2203%20da
YM2203 Japanese datasheet contents, translated: http://www.larwe.com/technical/chip_ym2203.html
*/
// additional modifications by tildearrow and Eulous for furnace (particularly AY8930 emulation)
#include "ay8910.h"
#include <stdio.h>
#include <math.h>
@ -1019,8 +1021,10 @@ void ay8910_device::ay8910_write_reg(int r, int v)
m_tone[2].set_duty(m_regs[AY_CDUTY]);
break;
case AY_NOISEAND:
m_noise_and=m_regs[AY_NOISEAND];
break;
case AY_NOISEOR:
// not implemented
m_noise_or=m_regs[AY_NOISEOR];
break;
default:
m_regs[r] = 0; // reserved, set as 0
@ -1080,13 +1084,36 @@ void ay8910_device::sound_stream_update(short** outputs, int outLen)
if (!m_prescale_noise || is_expanded_mode()) // AY8930 noise generator rate is twice compares as compatibility mode
{
/* 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. */
// TODO : get actually algorithm for AY8930
m_rng ^= (((m_rng & 1) ^ ((m_rng >> 3) & 1)) << 17);
m_rng >>= 1;
if (is_expanded_mode()) {
// This is called "Noise value" on the docs, but is a counter whose period is determined by the LFSR.
// Using AND/OR gates, specific periods can be "filtered" out.
// A square wave can be generated through this behavior, which can be used for crude AM pulse width modulation.
// The period of the noise is determined by this value.
// The least significant byte of the LFSR is bitwise ANDed with the AND mask, and then bitwise ORed with the OR mask.
unsigned int noiseValuePeriod = ((m_rng & 0xFF & m_noise_and) | m_noise_or);
// Clock the noise value.
if (m_noise_value >= noiseValuePeriod) {
m_noise_value = 0;
// When everything is finally said and done, a 1bit latch is flipped.
// This is the final output of the noise, to be multiplied by the tone and envelope generators of the channel.
m_noise_latch ^= 1;
// The 17-bit LFSR is updated, using an XOR across bits 0 and 2.
unsigned int feedback = (m_rng & 1) ^ ((m_rng >> 2) & 1);
m_rng >>= 1;
m_rng |= (feedback << 16);
}
m_noise_value++;
} else {
/* 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. */
m_rng ^= (((m_rng & 1) ^ ((m_rng >> 3) & 1)) << 17);
m_rng >>= 1;
}
}
}
@ -1242,6 +1269,10 @@ void ay8910_device::ay8910_reset_ym()
m_register_latch = 0;
m_rng = 1;
m_mode = 0; // ay-3-8910 compatible mode
m_noise_and = 0;
m_noise_or = 0;
m_noise_value = 0;
m_noise_latch = 0;
for (int chan = 0; chan < NUM_CHANNELS; chan++)
{
m_tone[chan].reset();
@ -1428,6 +1459,10 @@ ay8910_device::ay8910_device(device_type type, unsigned int clock,
m_prescale_noise(0),
m_count_noise(0),
m_rng(0),
m_noise_and(0),
m_noise_or(0),
m_noise_value(0),
m_noise_latch(0),
m_mode(0),
m_env_step_mask((!(feature & PSG_HAS_EXPANDED_MODE)) && (psg_type == PSG_TYPE_AY) ? 0x0f : 0x1f),
m_step( (!(feature & PSG_HAS_EXPANDED_MODE)) && (psg_type == PSG_TYPE_AY) ? 2 : 1),

4
src/engine/platform/sound/ay8910.h
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@ -292,6 +292,10 @@ private:
unsigned char m_prescale_noise;
int m_count_noise;
int m_rng;
unsigned int m_noise_and;
unsigned int m_noise_or;
unsigned int m_noise_value;
unsigned int m_noise_latch;
unsigned char m_mode;
unsigned char m_env_step_mask;
/* init parameters ... */

8
src/engine/playback.cpp
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@ -76,6 +76,8 @@ const char* cmdName[DIV_CMD_MAX]={
"AY_ENVELOPE_LOW",
"AY_ENVELOPE_HIGH",
"AY_ENVELOPE_SLIDE",
"AY_NOISE_MASK_AND",
"AY_NOISE_MASK_OR",
"SAA_ENVELOPE",
@ -359,6 +361,12 @@ bool DivEngine::perSystemPostEffect(int ch, unsigned char effect, unsigned char
case 0x26: // envelope slide down
dispatchCmd(DivCommand(DIV_CMD_AY_ENVELOPE_SLIDE,ch,effectVal));
break;
case 0x27: // noise and mask
dispatchCmd(DivCommand(DIV_CMD_AY_NOISE_MASK_AND,ch,effectVal));
break;
case 0x28: // noise or mask
dispatchCmd(DivCommand(DIV_CMD_AY_NOISE_MASK_OR,ch,effectVal));
break;
}
break;
case DIV_SYSTEM_SAA1099: