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SameBoy/Core/apu.c

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C
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#include <stdint.h>
#include <math.h>
#include <string.h>
#include "apu.h"
#include "gb.h"
#define max(a,b) \
({ __typeof__ (a) _a = (a); \
__typeof__ (b) _b = (b); \
_a > _b ? _a : _b; })
#define min(a,b) \
({ __typeof__ (a) _a = (a); \
__typeof__ (b) _b = (b); \
_a < _b ? _a : _b; })
static __attribute__((unused)) int16_t generate_sin(double phase, int16_t amplitude)
{
return (int16_t)(sin(phase) * amplitude);
}
static int16_t generate_square(double phase, int16_t amplitude, double duty)
{
if (fmod(phase, 2 * M_PI) > duty * 2 * M_PI) {
return amplitude;
}
return 0;
}
static int16_t generate_wave(double phase, int16_t amplitude, signed char *wave, unsigned char shift)
{
phase = fmod(phase, 2 * M_PI);
return ((wave[(int)(phase / (2 * M_PI) * 32)]) >> shift) * (int)amplitude / 0xF;
}
static int16_t generate_noise(double phase, int16_t amplitude, uint16_t lfsr)
{
if (lfsr & 1) {
return amplitude;
}
return 0;
}
static int16_t step_lfsr(uint16_t lfsr, bool uses_7_bit)
{
bool xor = (lfsr & 1) ^ ((lfsr & 2) >> 1);
lfsr >>= 1;
if (xor) {
lfsr |= 0x4000;
}
if (uses_7_bit) {
lfsr &= ~0x40;
if (xor) {
lfsr |= 0x40;
}
}
return lfsr;
}
/* General Todo: The APU emulation seems to fail many accuracy tests. It might require a rewrite with
these tests in mind. */
void apu_render(GB_gameboy_t *gb, unsigned long sample_rate, unsigned long n_samples, int16_t *samples)
{
for (; n_samples--; samples++) {
*samples = 0;
if (!gb->apu.global_enable) {
continue;
}
gb->io_registers[GB_IO_PCM_12] = 0;
gb->io_registers[GB_IO_PCM_34] = 0;
// Todo: Stereo support
if (gb->apu.left_on[0] || gb->apu.right_on[0]) {
int16_t sample = generate_square(gb->apu.wave_channels[0].phase,
gb->apu.wave_channels[0].amplitude,
gb->apu.wave_channels[0].duty);
*samples += sample;
gb->io_registers[GB_IO_PCM_12] = ((int)sample) * 0xF / MAX_CH_AMP;
}
if (gb->apu.left_on[1] || gb->apu.right_on[1]) {
int16_t sample = generate_square(gb->apu.wave_channels[1].phase,
gb->apu.wave_channels[1].amplitude,
gb->apu.wave_channels[1].duty);
*samples += sample;
gb->io_registers[GB_IO_PCM_12] |= (((int)sample) * 0xF / MAX_CH_AMP) << 4;
}
if (gb->apu.wave_enable && (gb->apu.left_on[2] || gb->apu.right_on[2])) {
int16_t sample = generate_wave(gb->apu.wave_channels[2].phase,
MAX_CH_AMP,
gb->apu.wave_form,
gb->apu.wave_shift);
*samples += sample;
gb->io_registers[GB_IO_PCM_34] = ((int)sample) * 0xF / MAX_CH_AMP;
}
if (gb->apu.left_on[3] || gb->apu.right_on[3]) {
int16_t sample = generate_noise(gb->apu.wave_channels[3].phase,
gb->apu.wave_channels[3].amplitude,
gb->apu.lfsr);
*samples += sample;
gb->io_registers[GB_IO_PCM_34] |= (((int)sample) * 0xF / MAX_CH_AMP) << 4;
}
*samples *= gb->apu.left_volume;
for (unsigned char i = 0; i < 4; i++) {
/* Phase */
gb->apu.wave_channels[i].phase += 2 * M_PI * gb->apu.wave_channels[i].frequency / sample_rate;
while (gb->apu.wave_channels[i].phase >= 2 * M_PI) {
if (i == 3) {
gb->apu.lfsr = step_lfsr(gb->apu.lfsr, gb->apu.lfsr_7_bit);
}
gb->apu.wave_channels[i].phase -= 2 * M_PI;
}
/* Stop on Length */
if (gb->apu.wave_channels[i].stop_on_length) {
if (gb->apu.wave_channels[i].sound_length > 0) {
gb->apu.wave_channels[i].sound_length -= 1.0 / sample_rate;
}
if (gb->apu.wave_channels[i].sound_length <= 0) {
gb->apu.wave_channels[i].amplitude = 0;
gb->apu.wave_channels[i].is_playing = false;
gb->apu.wave_channels[i].sound_length = i == 2? 1 : 0.25;
}
}
}
gb->apu.envelope_step_timer += 1.0 / sample_rate;
if (gb->apu.envelope_step_timer >= 1.0 / 64) {
gb->apu.envelope_step_timer -= 1.0 / 64;
for (unsigned char i = 0; i < 4; i++) {
if (gb->apu.wave_channels[i].envelope_steps && !--gb->apu.wave_channels[i].cur_envelope_steps) {
gb->apu.wave_channels[i].amplitude = min(max(gb->apu.wave_channels[i].amplitude + gb->apu.wave_channels[i].envelope_direction * CH_STEP, 0), MAX_CH_AMP);
gb->apu.wave_channels[i].cur_envelope_steps = gb->apu.wave_channels[i].envelope_steps;
}
}
}
gb->apu.sweep_step_timer += 1.0 / sample_rate;
if (gb->apu.sweep_step_timer >= 1.0 / 128) {
gb->apu.sweep_step_timer -= 1.0 / 128;
if (gb->apu.wave_channels[0].sweep_steps && !--gb->apu.wave_channels[0].cur_sweep_steps) {
// Convert back to GB format
unsigned short temp = (unsigned short) (2048 - 131072 / gb->apu.wave_channels[0].frequency);
// Apply sweep
temp = temp + gb->apu.wave_channels[0].sweep_direction *
(temp / (1 << gb->apu.wave_channels[0].sweep_shift));
if (temp > 2047) {
temp = 0;
}
// Back to frequency
gb->apu.wave_channels[0].frequency = 131072.0 / (2048 - temp);
gb->apu.wave_channels[0].cur_sweep_steps = gb->apu.wave_channels[0].sweep_steps;
}
}
}
}
void apu_run(GB_gameboy_t *gb)
{
static bool should_log_overflow = true;
while (gb->audio_copy_in_progress);
double ticks_per_sample = (double) CPU_FREQUENCY / gb->sample_rate;
while (gb->apu_cycles > ticks_per_sample) {
int16_t sample = 0;
apu_render(gb, gb->sample_rate, 1, &sample);
gb->apu_cycles -= ticks_per_sample;
if (gb->audio_position == gb->buffer_size) {
/*
if (should_log_overflow && !gb->turbo) {
gb_log(gb, "Audio overflow\n");
should_log_overflow = false;
}
*/
}
else {
gb->audio_buffer[gb->audio_position++] = sample;
should_log_overflow = true;
}
}
}
void apu_copy_buffer(GB_gameboy_t *gb, int16_t *dest, unsigned int count)
{
gb->audio_copy_in_progress = true;
if (!gb->audio_stream_started) {
// Intentionally fail the first copy to sync the stream with the Gameboy.
gb->audio_stream_started = true;
gb->audio_position = 0;
}
if (count > gb->audio_position) {
// gb_log(gb, "Audio underflow: %d\n", count - gb->audio_position);
memset(dest + gb->audio_position, 0, (count - gb->audio_position) * 2);
count = gb->audio_position;
}
memcpy(dest, gb->audio_buffer, count * 2);
memmove(gb->audio_buffer, gb->audio_buffer + count, (gb->audio_position - count) * 2);
gb->audio_position -= count;
gb->audio_copy_in_progress = false;
}
void apu_init(GB_gameboy_t *gb)
{
memset(&gb->apu, 0, sizeof(gb->apu));
gb->apu.wave_channels[0].duty = gb->apu.wave_channels[1].duty = 0.5;
gb->apu.lfsr = 0x7FFF;
gb->apu.left_volume = 1.0;
gb->apu.right_volume = 1.0;
for (int i = 0; i < 4; i++) {
gb->apu.left_on[i] = gb->apu.right_on[i] = 1;
}
}
unsigned char apu_read(GB_gameboy_t *gb, unsigned char reg)
{
/* Todo: what happens when reading from the wave from while it's playing? */
if (reg == GB_IO_NR52) {
unsigned char value = 0;
for (int i = 0; i < 4; i++) {
value >>= 1;
if (gb->apu.wave_channels[i].is_playing) {
value |= 0x8;
}
}
if (gb->apu.global_enable) {
value |= 0x80;
}
value |= 0x70;
return value;
}
static const char read_mask[GB_IO_WAV_END - GB_IO_NR10 + 1] = {
/* NRX0 NRX1 NRX2 NRX3 NRX4 */
0x80, 0x3F, 0x00, 0xFF, 0xBF, // NR1X
0xFF, 0x3F, 0x00, 0xFF, 0xBF, // NR2X
0x7F, 0xFF, 0x9F, 0xFF, 0xBF, // NR3X
0xFF, 0xFF, 0x00, 0x00, 0xBF, // NR4X
0x00, 0x00, 0x70, 0xFF, 0xFF, // NR5X
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // Unused
// Wave RAM
0, /* ... */
};
if (reg >= GB_IO_WAV_START && reg <= GB_IO_WAV_END && gb->apu.wave_channels[2].is_playing) {
return (unsigned char)((gb->display_cycles * 22695477 * reg) >> 8); // Semi-random but deterministic
}
return gb->io_registers[reg] | read_mask[reg - GB_IO_NR10];
}
void apu_write(GB_gameboy_t *gb, unsigned char reg, unsigned char value)
{
static const double duties[] = {0.125, 0.25, 0.5, 0.75};
static uint16_t NRX3_X4_temp[3] = {0};
unsigned char channel = 0;
if (!gb->apu.global_enable && reg != GB_IO_NR52) {
return;
}
gb->io_registers[reg] = value;
switch (reg) {
case GB_IO_NR10:
case GB_IO_NR11:
case GB_IO_NR12:
case GB_IO_NR13:
case GB_IO_NR14:
channel = 0;
break;
case GB_IO_NR21:
case GB_IO_NR22:
case GB_IO_NR23:
case GB_IO_NR24:
channel = 1;
break;
case GB_IO_NR33:
case GB_IO_NR34:
channel = 2;
break;
case GB_IO_NR41:
case GB_IO_NR42:
channel = 3;
default:
break;
}
switch (reg) {
case GB_IO_NR10:
gb->apu.wave_channels[channel].sweep_direction = value & 8? -1 : 1;
gb->apu.wave_channels[channel].cur_sweep_steps =
gb->apu.wave_channels[channel].sweep_steps = (value & 0x70) >> 4;
gb->apu.wave_channels[channel].sweep_shift = value & 7;
break;
case GB_IO_NR11:
case GB_IO_NR21:
case GB_IO_NR41:
gb->apu.wave_channels[channel].duty = duties[value >> 6];
gb->apu.wave_channels[channel].sound_length = (64 - (value & 0x3F)) / 256.0;
if (gb->apu.wave_channels[channel].sound_length == 0) {
gb->apu.wave_channels[channel].is_playing = false;
}
break;
case GB_IO_NR12:
case GB_IO_NR22:
case GB_IO_NR42:
gb->apu.wave_channels[channel].start_amplitude =
gb->apu.wave_channels[channel].amplitude = CH_STEP * (value >> 4);
if (value >> 4 == 0) {
gb->apu.wave_channels[channel].is_playing = false;
}
gb->apu.wave_channels[channel].envelope_direction = value & 8? 1 : -1;
gb->apu.wave_channels[channel].cur_envelope_steps =
gb->apu.wave_channels[channel].envelope_steps = value & 7;
break;
case GB_IO_NR13:
case GB_IO_NR23:
case GB_IO_NR33:
NRX3_X4_temp[channel] = (NRX3_X4_temp[channel] & 0xFF00) | value;
gb->apu.wave_channels[channel].frequency = 131072.0 / (2048 - NRX3_X4_temp[channel]);
if (channel == 2) {
gb->apu.wave_channels[channel].frequency /= 2;
}
break;
case GB_IO_NR14:
case GB_IO_NR24:
case GB_IO_NR34:
gb->apu.wave_channels[channel].stop_on_length = value & 0x40;
if (value & 0x80) {
gb->apu.wave_channels[channel].is_playing = true;
gb->apu.wave_channels[channel].phase = 0;
gb->apu.wave_channels[channel].amplitude = gb->apu.wave_channels[channel].start_amplitude;
gb->apu.wave_channels[channel].cur_envelope_steps = gb->apu.wave_channels[channel].envelope_steps;
}
NRX3_X4_temp[channel] = (NRX3_X4_temp[channel] & 0xFF) | ((value & 0x7) << 8);
gb->apu.wave_channels[channel].frequency = 131072.0 / (2048 - NRX3_X4_temp[channel]);
if (channel == 2) {
gb->apu.wave_channels[channel].frequency /= 2;
}
break;
case GB_IO_NR30:
gb->apu.wave_enable = value & 0x80;
break;
case GB_IO_NR31:
gb->apu.wave_channels[2].sound_length = (256 - value) / 256.0;
if (gb->apu.wave_channels[2].sound_length == 0) {
gb->apu.wave_channels[2].is_playing = false;
}
break;
case GB_IO_NR32:
gb->apu.wave_shift = ((value >> 5) + 3) & 3;
break;
case GB_IO_NR43:
{
double r = value & 0x7;
if (r == 0) r = 0.5;
unsigned char s = value >> 4;
gb->apu.wave_channels[3].frequency = 524288.0 / r / (1 << (s + 1));
gb->apu.lfsr_7_bit = value & 0x8;
break;
}
case GB_IO_NR44:
gb->apu.wave_channels[3].stop_on_length = value & 0x40;
if (value & 0x80) {
gb->apu.wave_channels[3].is_playing = true;
gb->apu.lfsr = 0x7FFF;
gb->apu.wave_channels[3].amplitude = gb->apu.wave_channels[3].start_amplitude;
gb->apu.wave_channels[3].cur_envelope_steps = gb->apu.wave_channels[3].envelope_steps;
}
break;
case GB_IO_NR50:
gb->apu.left_volume = (value & 7) / 7.0;
gb->apu.right_volume = ((value >> 4) & 7) / 7.0;
break;
case GB_IO_NR51:
for (int i = 0; i < 4; i++) {
gb->apu.left_on[i] = value & 1;
gb->apu.right_on[i] = value & 0x10;
value >>= 1;
}
break;
case GB_IO_NR52:
if ((value & 0x80) && !gb->apu.global_enable) {
apu_init(gb);
gb->apu.global_enable = true;
}
else if (!(value & 0x80) && gb->apu.global_enable) {
memset(&gb->apu, 0, sizeof(gb->apu));
memset(gb->io_registers + GB_IO_NR10, 0, GB_IO_WAV_START - GB_IO_NR10);
}
break;
default:
if (reg >= GB_IO_WAV_START && reg <= GB_IO_WAV_END) {
gb->apu.wave_form[(reg - GB_IO_WAV_START) * 2] = value >> 4;
gb->apu.wave_form[(reg - GB_IO_WAV_START) * 2 + 1] = value & 0xF;
}
break;
}
}
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