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Reset period counter when writing to period registers.

Browse source 
This is what happens on real SCC. See also e.g. openMSX core:
https://github.com/openMSX/openMSX/blob/master/src/sound/SCC.cc#L390

To reduce the noise introduced by this, we add extra checks to only
write the period when it has actually changed.
This commit is contained in:
Laurens Holst 2022-05-13 16:34:48 +02:00
parent 34d868522b
commit e2c1233b12
3 changed files with 12 additions and 3 deletions
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10
src/engine/platform/scc.cpp
View file

@ -161,9 +161,14 @@ void DivPlatformSCC::tick(bool sysTick) {
chan[i].freq=parent->calcFreq(chan[i].baseFreq,chan[i].pitch,true,0,chan[i].pitch2,chipClock,CHIP_DIVIDER)-1;
if (chan[i].freq<0) chan[i].freq=0;
if (chan[i].freq>4095) chan[i].freq=4095;
rWrite(regBase+0+i*2,chan[i].freq&0xff);
rWrite(regBase+1+i*2,chan[i].freq>>8);
if (!chan[i].freqInit || regPool[regBase+0+i*2]!=(chan[i].freq&0xff)) {
rWrite(regBase+0+i*2,chan[i].freq&0xff);
}
if (!chan[i].freqInit || regPool[regBase+1+i*2]!=(chan[i].freq>>8)) {
rWrite(regBase+1+i*2,chan[i].freq>>8);
}
chan[i].freqChanged=false;
chan[i].freqInit=!skipRegisterWrites;
}
}
}
@ -286,6 +291,7 @@ void DivPlatformSCC::forceIns() {
for (int i=0; i<5; i++) {
chan[i].insChanged=true;
chan[i].freqChanged=true;
chan[i].freqInit=false;
if (isPlus || i<3) {
updateWave(i);
}

3
src/engine/platform/scc.h
View file

@ -29,7 +29,7 @@
class DivPlatformSCC: public DivDispatch {
struct Channel {
int freq, baseFreq, pitch, pitch2, note, ins;
bool active, insChanged, freqChanged, inPorta;
bool active, insChanged, freqChanged, freqInit, inPorta;
signed char vol, outVol, wave;
signed char waveROM[32] = {0}; // 4 bit PROM per channel on bubble system
DivMacroInt std;
@ -48,6 +48,7 @@ class DivPlatformSCC: public DivDispatch {
active(false),
insChanged(true),
freqChanged(false),
freqInit(false),
inPorta(false),
vol(15),
outVol(15),

2
src/engine/platform/sound/scc/scc.cpp
View file

@ -454,6 +454,7 @@ void scc_core::freq_vol_enable_w(u8 address, u8 data)
if (m_test.resetpos) // Reset address
m_voice[voice_freq].addr = 0;
m_voice[voice_freq].pitch = (m_voice[voice_freq].pitch & ~0x0ff) | data;
m_voice[voice_freq].counter = m_voice[voice_freq].pitch;
break;
case 0x1: // 0x*1 Voice 0 Pitch MSB
case 0x3: // 0x*3 Voice 1 Pitch MSB
@ -463,6 +464,7 @@ void scc_core::freq_vol_enable_w(u8 address, u8 data)
if (m_test.resetpos) // Reset address
m_voice[voice_freq].addr = 0;
m_voice[voice_freq].pitch = (m_voice[voice_freq].pitch & ~0xf00) | (u16(bitfield(data, 0, 4)) << 8);
m_voice[voice_freq].counter = m_voice[voice_freq].pitch;
break;
case 0xa: // 0x*a Voice 0 Volume
case 0xb: // 0x*b Voice 1 Volume