Genesis-Plus-GX/source/sound/sn76489.h

/* 
    SN76489 emulation
    by Maxim in 2001 and 2002
    converted from my original Delphi implementation

    I'm a C newbie so I'm sure there are loads of stupid things
    in here which I'll come back to some day and redo

    Includes:
    - Super-high quality tone channel "oversampling" by calculating fractional positions on transitions
    - Noise output pattern reverse engineered from actual SMS output
    - Volume levels taken from actual SMS output

    07/08/04  Charles MacDonald
    Modified for use with SMS Plus:
    - Added support for multiple PSG chips.
    - Added reset/config/update routines.
    - Added context management routines.
    - Removed SN76489_GetValues().
    - Removed some unused variables.

   25/04/07 Eke-Eke (Genesis Plus GX)
    - Removed stereo GG support (unused)
    - Rade SN76489_Update outputs 16bits mono samples
    - Replaced volume table with VGM plugin's one

   05/01/09 Eke-Eke (Genesis Plus GX)
    - Modified Cut-Off frequency (according to Steve Snake: http://www.smspower.org/forums/viewtopic.php?t=1746)

   25/05/09 Eke-Eke (Genesis Plus GX)
    - Removed multichip support (unused)
    - Removed alternate volume table, panning & mute support (unused)
    - Removed configurable Feedback and Shift Register Width (always use Sega ones)
    - Added linear resampling using Blip Buffer (Blargg's implementation: http://www.smspower.org/forums/viewtopic.php?t=11376)
*/

#ifndef _SN76489_H_
#define _SN76489_H_

/* SN76489 clone in Sega's VDP chips (315-5124, 315-5246, 315-5313, Game Gear) */
#define FB_SEGAVDP  0x0009
#define SRW_SEGAVDP 16

typedef struct
{
  /* Configuration */
  int BoostNoise; // double noise volume when non-zero

  /* PSG registers: */
  int Registers[8];       /* Tone, vol x4 */
  int LatchedRegister;
  int NoiseShiftRegister;
  int NoiseFreq;          /* Noise channel signal generator frequency */

  /* Output calculation variables */
  int ToneFreqVals[4];    /* Frequency register values (counters) */
  int ToneFreqPos[4];     /* Frequency channel flip-flops */
  int Channels[4];        /* Value of each channel, before stereo is applied */

  /* Blip-Buffer variables */
  struct blip_buffer_t* blip_buffer;  /* delta resampler */
  int chan_amp[4];                    /* current channel amplitudes in delta buffers */

} SN76489_Context;

/* Function prototypes */
extern void SN76489_Init(int PSGClockValue, int SamplingRate);
extern void SN76489_Reset(void);
extern void SN76489_Shutdown(void);
extern void SN76489_SetContext(uint8 *data);
extern void SN76489_GetContext(uint8 *data);
extern uint8 *SN76489_GetContextPtr(void);
extern int SN76489_GetContextSize(void);
extern void SN76489_Write(int data);
extern void SN76489_Update(INT16 *buffer, int length);
extern void SN76489_BoostNoise(int boost);

#endif /* _SN76489_H_ */