bsnes/Core/apu.h

#ifndef apu_h
#define apu_h
#include <stdbool.h>
#include <stdint.h>
#include <stddef.h>
#include "gb_struct_def.h"


#ifdef GB_INTERNAL
/* Speed = 1 / Length (in seconds) */
/* Todo: Measure these  and find the actual curve shapes.
   They are known to be incorrect (Some analog test ROM sound different),
   but are good enough approximations to fix Cannon Fodder's terrible audio.
   It also varies by model. */
#define DAC_DECAY_SPEED 50000
#define DAC_ATTACK_SPEED 1000


/* Divides nicely and never overflows with 4 channels and 8 (1-8) volume levels */
#ifdef WIIU
/* Todo: Remove this hack once https://github.com/libretro/RetroArch/issues/6252 is fixed*/
#define MAX_CH_AMP (0xFF0 / 2)
#else
#define MAX_CH_AMP 0xFF0
#endif
#define CH_STEP (MAX_CH_AMP/0xF/8)
#endif



/* APU ticks are 2MHz, triggered by an internal APU clock. */

typedef struct
{
    int16_t left;
    int16_t right;
} GB_sample_t;

typedef struct
{
    double left;
    double right;
} GB_double_sample_t;

enum GB_CHANNELS {
    GB_SQUARE_1,
    GB_SQUARE_2,
    GB_WAVE,
    GB_NOISE,
    GB_N_CHANNELS
};

typedef struct
{
    bool global_enable;
    uint8_t apu_cycles;
    
    uint8_t samples[GB_N_CHANNELS];
    bool is_active[GB_N_CHANNELS];
    
    uint8_t div_divider; // The DIV register ticks the APU at 512Hz, but is then divided
                         // once more to generate 128Hz and 64Hz clocks
    
    uint8_t lf_div; // The APU runs in 2MHz, but channels 1, 2 and 4 run in 1MHZ so we divide
                    // need to divide the signal.
    
    uint8_t square_sweep_countdown; // In 128Hz
    uint8_t square_sweep_calculate_countdown; // In 2 MHz
    uint16_t new_sweep_sample_legnth;
    uint16_t shadow_sweep_sample_legnth;
    bool sweep_enabled;
    bool sweep_decreasing;
    
    struct {
        uint16_t pulse_length; // Reloaded from NRX1 (xorred), in 256Hz DIV ticks
        uint8_t current_volume; // Reloaded from NRX2
        uint8_t volume_countdown; // Reloaded from NRX2
        uint8_t current_sample_index; /* For save state compatibility,
                                         highest bit is reused (See NR14/NR24's
                                         write code)*/
        
        uint16_t sample_countdown; // in APU ticks (Reloaded from sample_length, xorred $7FF)
        uint16_t sample_length; // From NRX3, NRX4, in APU ticks
        bool length_enabled; // NRX4

    } square_channels[2];
    
    struct {
        bool enable; // NR30
        uint16_t pulse_length; // Reloaded from NR31 (xorred), in 256Hz DIV ticks
        uint8_t shift; // NR32
        uint16_t sample_length; // NR33, NR34, in APU ticks
        bool length_enabled; // NR34
        
        uint16_t sample_countdown; // in APU ticks (Reloaded from sample_length, xorred $7FF)
        uint8_t current_sample_index;
        uint8_t current_sample; // Current sample before shifting.
        
        int8_t wave_form[32];
        bool wave_form_just_read;
    } wave_channel;
    
    struct {
        uint16_t pulse_length; // Reloaded from NR41 (xorred), in 256Hz DIV ticks
        uint8_t current_volume; // Reloaded from NR42
        uint8_t volume_countdown; // Reloaded from NR42
        uint16_t lfsr;
        bool narrow;
        
        uint16_t sample_countdown; // in APU ticks (Reloaded from sample_length)
        uint16_t sample_length; // From NR43, in APU ticks
        bool length_enabled; // NR44
        
        uint8_t alignment; // If (NR43 & 7) != 0, samples are aligned to 512KHz clock instead of
                           // 1MHz. This variable keeps track of the alignment.
        
    } noise_channel;
    
    bool skip_div_event;
    bool current_lfsr_sample;
    bool previous_lfsr_sample;
} GB_apu_t;

typedef enum {
    GB_HIGHPASS_OFF, // Do not apply any filter, keep DC offset
    GB_HIGHPASS_ACCURATE, // Apply a highpass filter similar to the one used on hardware
    GB_HIGHPASS_REMOVE_DC_OFFSET, // Remove DC Offset without affecting the waveform
    GB_HIGHPASS_MAX
} GB_highpass_mode_t;

typedef struct {
    unsigned sample_rate;
    
    GB_sample_t *buffer;
    size_t buffer_size;
    size_t buffer_position;
    
    bool stream_started; /* detects first copy request to minimize lag */
    volatile bool copy_in_progress;
    volatile bool lock;
    
    double sample_cycles; // In 8 MHz units
    
    // Samples are NOT normalized to MAX_CH_AMP * 4 at this stage!
    unsigned cycles_since_render;
    unsigned last_update[GB_N_CHANNELS];
    GB_sample_t current_sample[GB_N_CHANNELS];
    GB_sample_t summed_samples[GB_N_CHANNELS];
    double dac_discharge[GB_N_CHANNELS];
    
    GB_highpass_mode_t highpass_mode;
    double highpass_rate;
    GB_double_sample_t highpass_diff;
} GB_apu_output_t;

void GB_set_sample_rate(GB_gameboy_t *gb, unsigned int sample_rate);
void GB_apu_copy_buffer(GB_gameboy_t *gb, GB_sample_t *dest, size_t count);
size_t GB_apu_get_current_buffer_length(GB_gameboy_t *gb);
void GB_set_highpass_filter_mode(GB_gameboy_t *gb, GB_highpass_mode_t mode);

#ifdef GB_INTERNAL
void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value);
uint8_t GB_apu_read(GB_gameboy_t *gb, uint8_t reg);
void GB_apu_div_event(GB_gameboy_t *gb);
void GB_apu_init(GB_gameboy_t *gb);
void GB_apu_run(GB_gameboy_t *gb);
#endif

#endif /* apu_h */