130 lines
3.7 KiB
C
130 lines
3.7 KiB
C
// Commander X16 Emulator
|
|
// Copyright (c) 2020 Frank van den Hoef
|
|
// All rights reserved. License: 2-clause BSD
|
|
|
|
// Chip revisions
|
|
// 0: V 0.3.0
|
|
// 1: V 47.0.0 (9-bit volume, phase reset on mute)
|
|
// 2: V 47.0.2 (Pulse Width XOR on Saw and Triangle)
|
|
|
|
#include "vera_psg.h"
|
|
|
|
#include <stdlib.h>
|
|
#include <string.h>
|
|
|
|
enum waveform {
|
|
WF_PULSE = 0,
|
|
WF_SAWTOOTH,
|
|
WF_TRIANGLE,
|
|
WF_NOISE,
|
|
};
|
|
|
|
static uint16_t volume_lut[64] = {0, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 6, 6, 7, 7, 7, 8, 8, 9, 9, 10, 11, 11, 12, 13, 14, 14, 15, 16, 17, 18, 19, 21, 22, 23, 25, 26, 28, 29, 31, 33, 35, 37, 39, 42, 44, 47, 50, 52, 56, 59, 63};
|
|
static uint16_t volume_lut_47[64] = {
|
|
0, 4, 8, 12,
|
|
16, 17, 18, 20, 21, 22, 23, 25, 26, 28, 30, 31,
|
|
33, 35, 37, 40, 42, 45, 47, 50, 53, 56, 60, 63,
|
|
67, 71, 75, 80, 85, 90, 95, 101, 107, 113, 120, 127,
|
|
135, 143, 151, 160, 170, 180, 191, 202, 214, 227, 241, 255,
|
|
270, 286, 303, 321, 341, 361, 382, 405, 429, 455, 482, 511
|
|
};
|
|
|
|
void
|
|
psg_reset(struct VERA_PSG* psg)
|
|
{
|
|
memset(psg->channels, 0, sizeof(psg->channels));
|
|
psg->noiseOut = 0;
|
|
psg->noiseState = 1;
|
|
}
|
|
|
|
void
|
|
psg_writereg(struct VERA_PSG* psg, uint8_t reg, uint8_t val)
|
|
{
|
|
reg &= 0x3f;
|
|
|
|
int ch = reg / 4;
|
|
int idx = reg & 3;
|
|
|
|
switch (idx) {
|
|
case 0: psg->channels[ch].freq = (psg->channels[ch].freq & 0xFF00) | val; break;
|
|
case 1: psg->channels[ch].freq = (psg->channels[ch].freq & 0x00FF) | (val << 8); break;
|
|
case 2: {
|
|
psg->channels[ch].right = (val & 0x80) != 0;
|
|
psg->channels[ch].left = (val & 0x40) != 0;
|
|
psg->channels[ch].volume = ((psg->chipType < 1) ? volume_lut : volume_lut_47)[val & 0x3F];
|
|
break;
|
|
}
|
|
case 3: {
|
|
psg->channels[ch].pw = val & 0x3F;
|
|
psg->channels[ch].waveform = val >> 6;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
static inline void
|
|
render(struct VERA_PSG* psg, int16_t *left, int16_t *right)
|
|
{
|
|
int l = 0;
|
|
int r = 0;
|
|
|
|
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];
|
|
|
|
unsigned new_phase = (ch->phase + ch->freq) & 0x1FFFF;
|
|
if ((psg->chipType >= 1) && (!ch->left && !ch->right)) {
|
|
new_phase = 0;
|
|
}
|
|
if ((ch->phase & 0x10000) != (new_phase & 0x10000)) {
|
|
ch->noiseval = (psg->chipType < 1) ? psg->noiseOut : (psg->noiseState >> 1) & 0x3f;
|
|
}
|
|
ch->phase = new_phase;
|
|
|
|
uint8_t v = 0;
|
|
switch (ch->waveform) {
|
|
case WF_PULSE: v = (ch->phase >> 10) > ch->pw ? 0 : 63; break;
|
|
case WF_SAWTOOTH: v = (ch->phase >> 11) ^ (psg->chipType < 2 ? 0 : (ch->pw ^ 0x3f) & 0x3f); break;
|
|
case WF_TRIANGLE: v = ((ch->phase & 0x10000) ? (~(ch->phase >> 10) & 0x3F) : ((ch->phase >> 10) & 0x3F)) ^ (psg->chipType < 2 ? 0 : (ch->pw ^ 0x3f) & 0x3f); break;
|
|
case WF_NOISE: v = ch->noiseval; break;
|
|
}
|
|
int8_t sv = (v ^ 0x20);
|
|
if (sv & 0x20) {
|
|
sv |= 0xC0;
|
|
}
|
|
|
|
int val = (int)sv * (int)ch->volume;
|
|
|
|
if (ch->left) {
|
|
l += (psg->chipType < 1) ? val : val >> 3;
|
|
}
|
|
if (ch->right) {
|
|
r += (psg->chipType < 1) ? val : val >> 3;
|
|
}
|
|
|
|
if (ch->left || ch->right) {
|
|
ch->lastOut = (psg->chipType < 1) ? val << 3 : val;
|
|
} else {
|
|
ch->lastOut = 0;
|
|
}
|
|
}
|
|
|
|
*left = l;
|
|
*right = r;
|
|
}
|
|
|
|
void
|
|
psg_render(struct VERA_PSG* psg, int16_t *bufL, int16_t *bufR, unsigned num_samples)
|
|
{
|
|
while (num_samples--) {
|
|
render(psg, bufL, bufR);
|
|
bufL++;
|
|
bufR++;
|
|
}
|
|
}
|