Spc_Dsp.h

Go to the documentation of this file.

// Fast SNES SPC-700 DSP emulator (about 3x speed of accurate one)
 
// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/
#ifndef SPC_DSP_H
#define SPC_DSP_H
 
#include "blargg_common.h"
 
struct Spc_Dsp {
public:
// Setup
        
        // Initializes DSP and has it use the 64K RAM provided
        void init( void* ram_64k );
 
        // Sets destination for output samples. If out is NULL or out_size is 0,
        // doesn't generate any.
        typedef short sample_t;
        void set_output( sample_t* out, int out_size );
 
        // Number of samples written to output since it was last set, always
        // a multiple of 2. Undefined if more samples were generated than
        // output buffer could hold.
        int sample_count() const;
 
// Emulation
        
        // Resets DSP to power-on state
        void reset();
 
        // Emulates pressing reset switch on SNES
        void soft_reset();
        
        // Reads/writes DSP registers. For accuracy, you must first call spc_run_dsp()
        // to catch the DSP up to present.
        int  read ( int addr ) const;
        void write( int addr, int data );
 
        // Runs DSP for specified number of clocks (~1024000 per second). Every 32 clocks
        // a pair of samples is be generated.
        void run( int clock_count );
 
// Sound control
 
        // Mutes voices corresponding to non-zero bits in mask (overrides VxVOL with 0).
        // Reduces emulation accuracy.
        enum { voice_count = 8 };
        void mute_voices( int mask );
 
        // If true, prevents channels and global volumes from being phase-negated
        void disable_surround( bool disable = true );
 
// State
        
        // Resets DSP and uses supplied values to initialize registers
        enum { register_count = 128 };
        void load( uint8_t const regs [register_count] );
 
// DSP register addresses
 
        // Global registers
        enum {
            r_mvoll = 0x0C, r_mvolr = 0x1C,
            r_evoll = 0x2C, r_evolr = 0x3C,
            r_kon   = 0x4C, r_koff  = 0x5C,
            r_flg   = 0x6C, r_endx  = 0x7C,
            r_efb   = 0x0D, r_pmon  = 0x2D,
            r_non   = 0x3D, r_eon   = 0x4D,
            r_dir   = 0x5D, r_esa   = 0x6D,
            r_edl   = 0x7D,
            r_fir   = 0x0F // 8 coefficients at 0x0F, 0x1F ... 0x7F
        };
 
        // Voice registers
        enum {
                v_voll   = 0x00, v_volr   = 0x01,
                v_pitchl = 0x02, v_pitchh = 0x03,
                v_srcn   = 0x04, v_adsr0  = 0x05,
                v_adsr1  = 0x06, v_gain   = 0x07,
                v_envx   = 0x08, v_outx   = 0x09
        };
 
public:
        enum { extra_size = 16 };
        sample_t* extra()               { return m.extra; }
        sample_t const* out_pos() const { return m.out; }
public:
        BLARGG_DISABLE_NOTHROW
        
        enum { echo_hist_size = 8 };
        
        enum env_mode_t { env_release, env_attack, env_decay, env_sustain };
        enum { brr_buf_size = 12 };
        struct voice_t
        {
                int buf [brr_buf_size*2];// decoded samples (twice the size to simplify wrap handling)
                int* buf_pos;           // place in buffer where next samples will be decoded
                int interp_pos;         // relative fractional position in sample (0x1000 = 1.0)
                int brr_addr;           // address of current BRR block
                int brr_offset;         // current decoding offset in BRR block
                int kon_delay;          // KON delay/current setup phase
                env_mode_t env_mode;
                int env;                // current envelope level
                int hidden_env;         // used by GAIN mode 7, very obscure quirk
                int volume [2];         // copy of volume from DSP registers, with surround disabled
                int enabled;            // -1 if enabled, 0 if muted
        };
private:
        struct state_t
        {
                uint8_t regs [register_count];
                
                // Echo history keeps most recent 8 samples (twice the size to simplify wrap handling)
                int echo_hist [echo_hist_size * 2] [2];
                int (*echo_hist_pos) [2]; // &echo_hist [0 to 7]
                
                int every_other_sample; // toggles every sample
                int kon;                // KON value when last checked
                int noise;
                int echo_offset;        // offset from ESA in echo buffer
                int echo_length;        // number of bytes that echo_offset will stop at
                int phase;              // next clock cycle to run (0-31)
                unsigned counters [4];
                
                int new_kon;
                int t_koff;
                
                voice_t voices [voice_count];
                
                unsigned* counter_select [32];
                
                // non-emulation state
                uint8_t* ram; // 64K shared RAM between DSP and SMP
                int mute_mask;
                int surround_threshold;
                sample_t* out;
                sample_t* out_end;
                sample_t* out_begin;
                sample_t extra [extra_size];
        };
        state_t m;
        
        void init_counter();
        void run_counter( int );
        void soft_reset_common();
        void write_outline( int addr, int data );
        void update_voice_vol( int addr );
};
 
#include <assert.h>
 
inline int Spc_Dsp::sample_count() const { return m.out - m.out_begin; }
 
inline int Spc_Dsp::read( int addr ) const
{
        assert( (unsigned) addr < register_count );
        return m.regs [addr];
}
 
inline void Spc_Dsp::update_voice_vol( int addr )
{
        int l = (int8_t) m.regs [addr + v_voll];
        int r = (int8_t) m.regs [addr + v_volr];
        
        if ( l * r < m.surround_threshold )
        {
                // signs differ, so negate those that are negative
                l ^= l >> 7;
                r ^= r >> 7;
        }
        
        voice_t& v = m.voices [addr >> 4];
        int enabled = v.enabled;
        v.volume [0] = l & enabled;
        v.volume [1] = r & enabled;
}
 
inline void Spc_Dsp::write( int addr, int data )
{
        assert( (unsigned) addr < register_count );
        
        m.regs [addr] = (uint8_t) data;
        int low = addr & 0x0F;
        if ( low < 0x2 ) // voice volumes
        {
                update_voice_vol( low ^ addr );
        }
        else if ( low == 0xC )
        {
                if ( addr == r_kon )
                        m.new_kon = (uint8_t) data;
                
                if ( addr == r_endx ) // always cleared, regardless of data written
                        m.regs [r_endx] = 0;
        }
}
 
inline void Spc_Dsp::disable_surround( bool disable )
{
        m.surround_threshold = disable ? 0 : -0x4000;
}
 
#define SPC_NO_COPY_STATE_FUNCS 1
 
#define SPC_LESS_ACCURATE 1
 
#endif