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 CLOCK_NTSC 53693175
#define CLOCK_PAL  53203424
#define SND_SIZE (snd.buffer_size * sizeof(int16))

/* Global variables */
t_bitmap bitmap;
t_snd snd;
uint8  vdp_rate;
uint16 lines_per_frame;
double Master_Clock;
uint32 m68cycles_per_line;
uint32 z80cycles_per_line;
uint32 aim_m68k;
uint32 count_m68k;
uint32 line_m68k;
uint32 aim_z80;
uint32 count_z80;
uint32 line_z80;
int32 current_z80;
uint8 odd_frame;
uint8 interlaced;
uint32 frame_cnt;
uint8 system_hw;

/* Function prototypes */
static void audio_update (void);

/****************************************************************
 * CPU execution managment
 ****************************************************************/

/* Interrupt Manager
   this is called before each new executed instruction
   only if interrupts have been updated 
 */
static inline void update_interrupts(void)
{
	uint8 latency = hvint_updated;
	hvint_updated = -1;

	if (vint_pending && (reg[1] & 0x20))
	{
    vint_triggered = 1;
    if (latency) count_m68k += m68k_execute(latency);
		m68k_set_irq(6);
	}
	else if (hint_pending && (reg[0] & 0x10))
	{
		m68k_set_irq(4);
	}
	else
	{
		m68k_set_irq(0);
	}
}

static inline void m68k_run (int cyc) 
{
	while (count_m68k < cyc)
	{
		/* check interrupts */
		if (hvint_updated >= 0) update_interrupts();

		/* execute a single instruction */
		count_m68k += m68k_execute(1);
	}
}

void z80_run (int cyc) 
{
  current_z80 = cyc - count_z80;
	if (current_z80 > 0) count_z80 += z80_execute(current_z80);
}

/****************************************************************
 * Virtual Genesis initialization
 ****************************************************************/
void system_init (void)
{
	/* PAL/NTSC timings */
	vdp_rate        = vdp_pal ? 50 : 60;
	lines_per_frame = vdp_pal ? 313 : 262;
	Master_Clock	  = vdp_pal ? (double)CLOCK_PAL : (double)CLOCK_NTSC;
	
	/* CPU cycles increments */
	z80cycles_per_line = 228;
	m68cycles_per_line = 488;

	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;
	frame_cnt   = 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)
{
	int line;
	
	/* reset cycles counts */
	count_m68k = 0;
  aim_m68k = 0;
  aim_z80 = 0;
	count_z80 = 0;
  fifo_write_cnt = 0;
  fifo_lastwrite = 0;

  /* increment frame counter */
  frame_cnt ++;

	if (!gen_running) return 0;

  /* Clear VBLANK & DMA BUSY flags */
  status &= 0xFFF5;

	/* Look for interlace mode change */
	uint8 old_interlaced = interlaced;
  interlaced = (reg[12] & 2) >> 1;
	if (old_interlaced != interlaced)
  {
		bitmap.viewport.changed = 2;
    im2_flag = ((reg[12] & 6) == 6) ? 1 : 0;
		odd_frame = 1;
	}

  /* Toggle even/odd field flag (interlaced modes only) */
  odd_frame ^= 1;
  if (odd_frame && interlaced) status |= 0x0010;
  else status &= 0xFFEF;

	/* Reset HCounter */
	h_counter = reg[10];

  /* Parse sprites for line 0 (done on line 261 or 312) */
	parse_satb (0x80);

	/* Line processing */
	for (line = 0; line < lines_per_frame; line ++)
	{
    /* Update VCounter */
		v_counter = line;

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

 		/* Update CPU cycle counters */
    line_m68k = aim_m68k;
		line_z80  = aim_z80;
    aim_z80  += z80cycles_per_line;
    aim_m68k += m68cycles_per_line;

		/* Check "soft reset" */
		if (line == resetline) gen_reset(0);

    /* Horizontal Interrupt */
		if (line <= bitmap.viewport.h)
		{
			if(--h_counter < 0)
			{
				h_counter = reg[10];
				hint_pending = 1;
        hvint_updated = 0;
				
        /* previous scanline was shortened (see below), we execute extra cycles on this line */
        if (line != 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 < bitmap.viewport.h)&&(h_counter == 0)) aim_m68k -= 36; 
		}

    /* Check if there is any DMA in progess */
    if (dma_length) dma_update();

    /* Render Line */
    if (!do_skip) 
    {
      render_line(line,odd_frame);
			if (line < (bitmap.viewport.h-1)) parse_satb(0x81 + line);
    }

		/* Vertical Retrace */
		if (line == bitmap.viewport.h)
		{
      /* update inputs */
      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 (approx. 14.7 us) */
      m68k_run(line_m68k + 84); /* need to take upcoming latency in account (Hurricanes, Outrunners) */
      if (zreset && !zbusreq) z80_run(line_z80 + 40);
      else count_z80 = line_z80 + 40;

			/* Vertical Interrupt */
      status |= 0x80;
      vint_pending = 1;
      hvint_updated = 30; /* Tyrants, Mega-Lo-Mania & Ex Mutant need some cycles to read VINT flag */
		}
    else if (zirq)
    {
      /* clear any pending Z80 interrupt */
      zirq = 0;
      z80_set_irq_line(0, CLEAR_LINE);
    }

		/* Process line */
		m68k_run(aim_m68k);
		if (zreset == 1 && zbusreq == 0) z80_run(aim_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)
{
	/* 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 (0);
	snd.sample_rate = rate;
	
	/* Calculate the sound buffer size (for one frame) */
	snd.buffer_size = (rate / vdp_rate);

	/* (re)allocate sound buffers */
	snd.fm.buffer[0] = realloc (snd.fm.buffer[0], snd.buffer_size * sizeof (int));
	snd.fm.buffer[1] = realloc (snd.fm.buffer[1], snd.buffer_size * sizeof (int));
	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);
	snd.psg.buffer = realloc (snd.psg.buffer, 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);
}

static int ll, rr;

static 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;

#ifdef NGC
	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 = ll * boost;
		r = rr * 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 NGC
		*sb++ = r; // RIGHT channel comes first
		*sb++ = l;
#elif DOS
		snd.buffer[0][i] = l;
		snd.buffer[1][i] = r;
#endif
	}

#ifdef NGC
	mixbuffer++;
	mixbuffer &= 0xf;
#endif
}