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Merge pull request #343 from AYCEdemo/petvic 

VIC-20: Make noise state consistent across inits
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tildearrow 2022-04-06 15:06:08 -05:00 committed by GitHub
parent 11c0995b23 ba8ee96069
commit 6fb2a2e7f5
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 16 additions and 12 deletions
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21
src/engine/platform/sound/vic20sound.c
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@ -85,7 +85,7 @@ static float voltagefunction[] = {
29465.88f, 29474.32f, 29482.76f, 29491.20f
};
static void vic_sound_clock(sound_vic20_t *snd, uint32_t cycles);
void vic_sound_clock(sound_vic20_t *snd, uint32_t cycles);
int vic_sound_machine_calculate_samples(sound_vic20_t *snd, int16_t *pbuf, int nr, int soc, int scc, uint32_t delta_t)
{
@ -128,10 +128,7 @@ int vic_sound_machine_calculate_samples(sound_vic20_t *snd, int16_t *pbuf, int n
return s;
}
static uint16_t noise_LFSR = 0x0000;
static uint8_t noise_LFSR0_old = 0;
static void vic_sound_clock(sound_vic20_t *snd, uint32_t cycles)
void vic_sound_clock(sound_vic20_t *snd, uint32_t cycles)
{
uint32_t i;
int j, enabled;
@ -155,7 +152,7 @@ static void vic_sound_clock(sound_vic20_t *snd, uint32_t cycles)
a = a ? a : 128;
snd->ch[j].ctr += a << chspeed;
enabled = (snd->ch[j].reg & 128) >> 7;
edge_trigger = (noise_LFSR & 1) & !noise_LFSR0_old;
edge_trigger = (snd->noise_LFSR & 1) & !snd->noise_LFSR0_old;
if((j != 3) || ((j == 3) && edge_trigger)) {
uint8_t shift = snd->ch[j].shift;
@ -163,16 +160,16 @@ static void vic_sound_clock(sound_vic20_t *snd, uint32_t cycles)
snd->ch[j].shift = shift;
}
if(j == 3) {
int bit3 = (noise_LFSR >> 3) & 1;
int bit12 = (noise_LFSR >> 12) & 1;
int bit14 = (noise_LFSR >> 14) & 1;
int bit15 = (noise_LFSR >> 15) & 1;
int bit3 = (snd->noise_LFSR >> 3) & 1;
int bit12 = (snd->noise_LFSR >> 12) & 1;
int bit14 = (snd->noise_LFSR >> 14) & 1;
int bit15 = (snd->noise_LFSR >> 15) & 1;
int gate1 = bit3 ^ bit12;
int gate2 = bit14 ^ bit15;
int gate3 = (gate1 ^ gate2) ^ 1;
int gate4 = (gate3 & enabled) ^ 1;
noise_LFSR0_old = noise_LFSR & 1;
noise_LFSR = (noise_LFSR << 1) | gate4;
snd->noise_LFSR0_old = snd->noise_LFSR & 1;
snd->noise_LFSR = (snd->noise_LFSR << 1) | gate4;
}
snd->ch[j].out = snd->ch[j].shift & (j == 3 ? enabled : 1);
}

4
src/engine/platform/sound/vic20sound.h
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@ -56,12 +56,16 @@ struct sound_vic20_s {
float highpassbeta;
float lowpassbuf;
float lowpassbeta;
uint16_t noise_LFSR;
uint8_t noise_LFSR0_old;
};
typedef struct sound_vic20_s sound_vic20_t;
int vic_sound_machine_init(sound_vic20_t *snd, int speed, int cycles_per_sec);
void vic_sound_machine_store(sound_vic20_t *snd, uint16_t addr, uint8_t value);
int vic_sound_machine_calculate_samples(sound_vic20_t *snd, int16_t *pbuf, int nr, int soc, int scc, uint32_t delta_t);
void vic_sound_clock(sound_vic20_t *snd, uint32_t cycles);
#ifdef __cplusplus
};

3
src/engine/platform/vic20.cpp
View File

@ -282,6 +282,9 @@ void DivPlatformVIC20::reset() {
vic_sound_machine_init(vic,rate,chipClock);
hasWaveWrite=false;
rWrite(14,15);
// hack: starting noise channel right away after this would result in a dead
// channel as the LFSR state is 0, so clock it a bit
vic_sound_clock(vic,4);
}
bool DivPlatformVIC20::isStereo() {