Genesis-Plus-GX/source/system.c

/***************************************************************************************
 *  Genesis Plus 1.2a
 *  Main Emulation
 *
 *  Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003  Charles Mac Donald (original code)
 *  modified by Eke-Eke (compatibility fixes & additional code), GC/Wii port
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 ****************************************************************************************/

#include "shared.h"

#define SND_SIZE (snd.buffer_size * sizeof(int16))

/* Global variables */
t_bitmap bitmap;
t_snd snd;
uint8  vdp_rate;
uint16 lines_per_frame;
uint32 aim_m68k;
uint32 count_m68k;
uint32 line_m68k;
uint32 hint_m68k;
uint32 aim_z80;
uint32 count_z80;
uint32 line_z80;
int32 current_z80;
uint8 odd_frame;
uint8 interlaced;
uint8 system_hw;

static inline void audio_update (void);

/****************************************************************
 * Virtual Genesis initialization
 ****************************************************************/
void system_init (void)
{
	/* PAL/NTSC timings */
	vdp_rate        = vdp_pal ? 50 : 60;
	lines_per_frame = vdp_pal ? 313 : 262;
	
	gen_init ();
	vdp_init ();
	render_init ();
  cart_hw_init();
}

/****************************************************************
 * Virtual Genesis Restart
 ****************************************************************/
void system_reset (void)
{
	aim_m68k	  = 0;
	count_m68k	= 0;
	line_m68k	  = 0;
	aim_z80		  = 0;
	count_z80	  = 0;
	line_z80	  = 0;
	current_z80	= 0;
	odd_frame	  = 0;
	interlaced	= 0;

	/* Cart Hardware reset */
	cart_hw_reset();		

	/* Hard reset */
	gen_reset (1); 
	vdp_reset ();
	render_reset ();
	io_reset();
	SN76489_Reset(0);

	/* Sound buffers reset */
	memset (snd.psg.buffer, 0, SND_SIZE);
	memset (snd.fm.buffer[0], 0, SND_SIZE*2);
	memset (snd.fm.buffer[1], 0, SND_SIZE*2);
}

/****************************************************************
 * Virtual Genesis shutdown
 ****************************************************************/
void system_shutdown (void)
{
	gen_shutdown ();
	vdp_shutdown ();
	render_shutdown ();
}

/****************************************************************
 * Virtual Genesis Frame emulation
 ****************************************************************/
int system_frame (int do_skip)
{
	if (!gen_running)
  {
    update_input();
    return 0;
	}
	
	/* reset cycles counts */
	count_m68k = 0;
  aim_m68k = 0;
  aim_z80 = 0;
	count_z80 = 0;
  fifo_write_cnt = 0;
  fifo_lastwrite = 0;

  /* update display settings */
  int line;
  int reset = resetline;
  int vdp_height  = bitmap.viewport.h;
  int end_line    = vdp_height + bitmap.viewport.y;
  int start_line  = lines_per_frame - bitmap.viewport.y;
	int old_interlaced = interlaced;
  interlaced = (reg[12] & 2) >> 1;
	if (old_interlaced != interlaced)
  {
		bitmap.viewport.changed = 2;
    im2_flag = ((reg[12] & 6) == 6);
		odd_frame = 1;
	}

  odd_frame ^= 1;

  /* clear VBLANK and DMA flags */
  status &= 0xFFF5;
  
  /* even/odd field flag (interlaced modes only) */
  if (odd_frame && interlaced) status |= 0x0010;
  else status &= 0xFFEF;

	/* reload HCounter */
	int h_counter = reg[10];

  /* parse sprites for line 0 (done on last line) */
	parse_satb (0x80);

	/* process frame */
	for (line = 0; line < lines_per_frame; line ++)
	{
    /* update VCounter */
		v_counter = line;

		/* update 6-Buttons or Menacer */
		input_update();

 		/* update CPU cycle counters */
    hint_m68k = count_m68k;
    line_m68k = aim_m68k;
		line_z80  = aim_z80;
    aim_z80  += z80cycles_per_line;
    aim_m68k += m68cycles_per_line;

		/* Soft Reset ? */
		if (line == reset)
    {
#ifdef NGC
      /* wait for RESET button to be released */
      if (!SYS_ResetButtonDown())
#endif
      gen_reset(0);
    }

    /* active display */
    if (line <= vdp_height)
		{
			/* H Interrupt */
      if(--h_counter < 0)
			{
				h_counter = reg[10];
				hint_pending = 1;
        if (reg[0] & 0x10) irq_status = (irq_status & 0xff) | 0x14;
				
        /* adjust timings to take further decrement in account (see below) */
        if ((line != 0) || (h_counter == 0)) aim_m68k += 36;
      }

      /* HINT will be triggered on next line, approx. 36 cycles before VDP starts line rendering */
      /* during this period, any VRAM/CRAM/VSRAM writes should NOT be taken in account before next line */
      /* as a result, current line is shortened */
      /* fix Lotus 1, Lotus 2 RECS, Striker, Zero the Kamikaze Squirell */
      if ((line < vdp_height) && (h_counter == 0)) aim_m68k -= 36;

      /* update DMA timings */
      if (dma_length) dma_update();

		  /* vertical retrace */
      if (line == vdp_height)
		  {
        /* render overscan */
        if ((line < end_line) && (!do_skip)) render_line(line, 1);

        /* update inputs (doing this here fix Warriors of Eternal Sun) */
        update_input();

        /* set VBLANK flag */
        status |= 0x08;

        /* Z80 interrupt is 16ms period (one frame) and 64us length (one scanline) */
			  zirq = 1;
			  z80_set_irq_line(0, ASSERT_LINE);  
			 
        /* delay between HINT, VBLANK and VINT (Dracula, OutRunners, VR Troopers) */
        m68k_run(line_m68k + 84);
        if (zreset && !zbusreq)
        {
          current_z80 = line_z80 + 39 - count_z80;
          if (current_z80 > 0) count_z80 += z80_execute(current_z80);
        }
        else count_z80 = line_z80 + 39;

			  /* V Interrupt */
        status |= 0x80;
        vint_pending = 1;

        /* 36 cycles latency after VINT occurence flag (Ex-Mutants, Tyrant) */
        if (reg[1] & 0x20) irq_status = (irq_status & 0xff) | 0x2416; 
      }
      else if (!do_skip) 
      {
        /* render scanline and parse sprites for line n+1 */
        render_line(line, 0);
        if (line < (vdp_height-1)) parse_satb(0x81 + line);
		  }
    }
    else
    {
      /* update DMA timings */
      if (dma_length) dma_update();

      /* render overscan */
      if ((!do_skip) && ((line < end_line) || (line >= start_line))) render_line(line, 1);

      /* clear any pending Z80 interrupt */
      if (zirq)
      {
        zirq = 0;
        z80_set_irq_line(0, CLEAR_LINE);
      }
    }

		/* process line */
		m68k_run(aim_m68k);
		if (zreset == 1 && zbusreq == 0)
    {
      current_z80 = aim_z80 - count_z80;
      if (current_z80 > 0) count_z80 += z80_execute(current_z80);
		}
		else count_z80 = aim_z80;
		
		/* SVP chip */
		if (svp) ssp1601_run(SVP_cycles);
	}

	audio_update ();
		
	return gen_running;
}

/****************************************************************
 *							Audio System 
 ****************************************************************/
int audio_init (int rate)
{
	/* Shutdown first */
  audio_shutdown();

	/* Clear the sound data context */
	memset (&snd, 0, sizeof (snd));

	/* Make sure the requested sample rate is valid */
	if (!rate || ((rate < 8000) | (rate > 48000))) return (-1);
	snd.sample_rate = rate;
	
	/* Calculate the sound buffer size (for one frame) */
	snd.buffer_size = (rate / vdp_rate);

#ifdef DOS
  /* output buffers */
  snd.buffer[0] = (int16 *) malloc(SND_SIZE);
	snd.buffer[1] = (int16 *) malloc(SND_SIZE);
	if (!snd.buffer[0] || !snd.buffer[1]) return (-1);
	memset (snd.buffer[0], 0, SND_SIZE);
	memset (snd.buffer[1], 0, SND_SIZE);
#endif

  /* YM2612 stream buffers */
  snd.fm.buffer[0] = (int *)malloc (SND_SIZE*2);
	snd.fm.buffer[1] = (int *)malloc (SND_SIZE*2);
	if (!snd.fm.buffer[0] || !snd.fm.buffer[1]) return (-1);
	memset (snd.fm.buffer[0], 0, SND_SIZE*2);
	memset (snd.fm.buffer[1], 0, SND_SIZE*2);

  /* SRC buffers */
  if (config.hq_fm && !config.fm_core)
  {
    snd.fm.src_out = (float *) malloc(snd.buffer_size*2*sizeof(float));
    if (!snd.fm.src_out) return (-1);
  }

	/* SN76489 stream buffers */
  snd.psg.buffer = (int16 *)malloc (SND_SIZE);
	if (!snd.psg.buffer) return (-1);
	memset (snd.psg.buffer, 0, SND_SIZE);

	/* Set audio enable flag */
	snd.enabled = 1;

	/* Initialize Sound Chips emulation */
	sound_init(rate);

	return (0);
}

void audio_shutdown(void)
{
	/* free sound buffers */
  if (snd.buffer[0])    free(snd.buffer[0]);
  if (snd.buffer[1])    free(snd.buffer[1]);
  if (snd.fm.buffer[0]) free(snd.fm.buffer[0]);
  if (snd.fm.buffer[1]) free(snd.fm.buffer[1]);
  if (snd.fm.src_out)   free(snd.fm.src_out);
  if (snd.psg.buffer)   free(snd.psg.buffer);
}

static int ll, rr;

static inline void audio_update (void)
{
	int i;
  int l, r;
  double psg_preamp = config.psg_preamp;
  double fm_preamp  = config.fm_preamp;
  int boost  = config.boost;
  int filter = config.filter;

#ifndef DOS
	int16 *sb = (int16 *) soundbuffer[mixbuffer];
#endif

	/* get remaining samples */
	sound_update();

	/* mix samples */
	for (i = 0; i < snd.buffer_size; i ++)
	{
		l = r = (int) ((double)snd.psg.buffer[i] * psg_preamp);
		l += (int) ((double)snd.fm.buffer[0][i] * fm_preamp);
		r += (int) ((double)snd.fm.buffer[1][i] * fm_preamp);
		snd.fm.buffer[0][i] = 0;
		snd.fm.buffer[1][i] = 0;
		snd.psg.buffer[i] = 0;

    /* single-pole low-pass filter (6 dB/octave) */
		if (filter)
		{
      l = (ll + l) >> 1;
		  r = (rr + r) >> 1;
      ll = l;
      rr = r;
    }

    /* boost volume if asked*/
		l = l * boost;
		r = r * boost;

		/* clipping */
		if (l > 32767) l = 32767;
		else if (l < -32768) l = -32768;
		if (r > 32767) r = 32767;
		else if (r < -32768) r = -32768;

		/* update sound buffer */
#ifdef DOS
		snd.buffer[0][i] = l;
		snd.buffer[1][i] = r;
#elif LSB_FIRST
		*sb++ = l;
		*sb++ = r;
#else
    *sb++ = r;
		*sb++ = l;
#endif
	}

#ifndef DOS
	mixbuffer++;
	mixbuffer &= 0xf;
#endif
}