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VERA: Run noise generation in each channel update

This commit is contained in:
Natt Akuma 2022-06-27 19:37:45 +07:00
parent fc489239c2
commit e2449d91f1
1 changed files with 14 additions and 10 deletions
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24
src/engine/platform/sound/vera_psg.c
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@ -20,8 +20,8 @@ void
psg_reset(struct VERA_PSG* psg) psg_reset(struct VERA_PSG* psg)
{ {
memset(psg->channels, 0, sizeof(psg->channels)); memset(psg->channels, 0, sizeof(psg->channels));
psg->noiseState=1; psg->noiseOut = 0;
psg->noiseOut=0; psg->noiseState = 1;
} }
void void
@ -54,10 +54,14 @@ render(struct VERA_PSG* psg, int16_t *left, int16_t *right)
{ {
int l = 0; int l = 0;
int r = 0; int r = 0;
psg->noiseOut=((psg->noiseOut<<1)|(psg->noiseState&1))&63;
psg->noiseState=(psg->noiseState<<1)|(((psg->noiseState>>1)^(psg->noiseState>>2)^(psg->noiseState>>4)^(psg->noiseState>>15))&1);
for (int i = 0; i < 16; i++) { for (int i = 0; i < 16; i++) {
// In FPGA implementation, noise values are generated every system clock and
// the channel update is run sequentially. So, even if both two channels are
// fetching a noise value in the same sample, they should have different values
psg->noiseOut = ((psg->noiseOut << 1) | (psg->noiseState & 1)) & 63;
psg->noiseState = (psg->noiseState << 1) | (((psg->noiseState >> 1) ^ (psg->noiseState >> 2) ^ (psg->noiseState >> 4) ^ (psg->noiseState >> 15)) & 1);
struct VERAChannel *ch = &psg->channels[i]; struct VERAChannel *ch = &psg->channels[i];
unsigned new_phase = (ch->phase + ch->freq) & 0x1FFFF; unsigned new_phase = (ch->phase + ch->freq) & 0x1FFFF;
@ -87,11 +91,11 @@ render(struct VERA_PSG* psg, int16_t *left, int16_t *right)
r += val; r += val;
} }
if (ch->left || ch->right) { if (ch->left || ch->right) {
ch->lastOut=val; ch->lastOut = val;
} else { } else {
ch->lastOut=0; ch->lastOut = 0;
} }
} }
*left = l; *left = l;
@ -104,6 +108,6 @@ psg_render(struct VERA_PSG* psg, int16_t *bufL, int16_t *bufR, unsigned num_samp
while (num_samples--) { while (num_samples--) {
render(psg, bufL, bufR); render(psg, bufL, bufR);
bufL++; bufL++;
bufR++; bufR++;
} }
} }