Genesis-Plus-GX/genplus-gx/source/memz80.c

/*
    memz80.c --
    Memory handlers for Z80 memory and port access, and the Z80 to
    VDP interface.
*/

#define LOG_PORT 0		/* 1= Log Z80 I/O port accesses */

#include "shared.h"


unsigned int cpu_readmem16(unsigned int address)
{
	switch ((address >> 13) & 7)
    {
		case 0:		/* Work RAM */
		case 1:
			return zram[address & 0x1FFF];

		case 2:		/* YM2612 */
			return fm_read (address & 3);

		case 3:		/* VDP */
			if ((address & 0xFF00) == 0x7F00) return z80_vdp_r (address);
			return 0xFF;

		default:	/* V-bus bank */
			return z80_read_banked_memory (zbank | (address & 0x7FFF));
	}

	return 0xFF;
}


void cpu_writemem16(unsigned int address, unsigned int data)
{
	switch ((address >> 13) & 7)
    {
		case 0:		/* Work RAM */
		case 1:
			zram[address & 0x1FFF] = data;
			return;

		case 2:		/* YM2612 */
			fm_write (address & 3, data);
			return;

		case 3:		/* Bank register and VDP */
			switch (address & 0xFF00)
			{
				case 0x6000:
					gen_bank_w (data & 1);
					return;

				case 0x7F00:
					z80_vdp_w (address, data);
					return;

				default:
					z80_unused_w (address, data);
					return;
			}
			return;

		default:	/* V-bus bank */
			z80_write_banked_memory (zbank | (address & 0x7FFF), data);
			return;
	}
}


int z80_vdp_r(int address)
{
	switch (address & 0xFF)
    {
		case 0x00:	/* VDP data port */
		case 0x02:
			return (vdp_data_r () >> 8) & 0xFF;

		case 0x01:	/* VDP data port */
		case 0x03:
			return (vdp_data_r () & 0xFF);

		case 0x04:	/* VDP control port */
		case 0x06:
			return (0xFF | ((vdp_ctrl_r () >> 8) & 3));

		case 0x05:	/* VDP control port */
		case 0x07:
			return (vdp_ctrl_r () & 0xFF);

		case 0x08:	/* HV counter */
		case 0x0A:
		case 0x0C:
		case 0x0E:
			return (vdp_hvc_r () >> 8) & 0xFF;

		case 0x09:	/* HV counter */
		case 0x0B:
		case 0x0D:
		case 0x0F:
			return (vdp_hvc_r () & 0xFF);

		case 0x10:	/* Unused (PSG) */
		case 0x11:
		case 0x12:
		case 0x13:
		case 0x14:
		case 0x15:
		case 0x16:
		case 0x17:
			return z80_lockup_r (address);

		case 0x18:	/* Unused */
		case 0x19:
		case 0x1A:
		case 0x1B:
			return z80_unused_r (address);

		case 0x1C:	/* Unused (test register) */
		case 0x1D:
		case 0x1E:
		case 0x1F:
			return z80_unused_r (address);

		default:	/* Invalid VDP addresses */
			return z80_lockup_r (address);
	}

	return 0xFF;
}


void z80_vdp_w(int address, int data)
{
	switch (address & 0xFF)
    {
		case 0x00:	/* VDP data port */
		case 0x01:
		case 0x02:
		case 0x03:
			vdp_data_w (data << 8 | data);
			return;

		case 0x04:	/* VDP control port */
		case 0x05:
		case 0x06:
		case 0x07:
			vdp_ctrl_w (data << 8 | data);
			return;

		case 0x08:	/* Unused (HV counter) */
		case 0x09:
		case 0x0A:
		case 0x0B:
		case 0x0C:
		case 0x0D:
		case 0x0E:
		case 0x0F:
			z80_lockup_w (address, data);
			return;

		case 0x11:	/* PSG */
		case 0x13:
		case 0x15:
		case 0x17:
			psg_write (data);
			return;

		case 0x10:	/* Unused */
		case 0x12:
		case 0x14:
		case 0x16:
		case 0x18:
		case 0x19:
		case 0x1A:
		case 0x1B:
			z80_unused_w (address, data);
			return;

		case 0x1C:	/* Test register */
		case 0x1D:
		case 0x1E:
		case 0x1F:
			vdp_test_w (data << 8 | data);
			return;

		default:	/* Invalid VDP addresses */
			z80_lockup_w (address, data);
			return;
	}
}


/*
    Port handlers. Ports are unused when not in Mark III compatability mode.

    Games that access ports anyway:
    - Thunder Force IV reads port $BF in it's interrupt handler.
*/

unsigned int cpu_readport16(unsigned int port)
{
#if LOG_PORT
  error ("Z80 read port %04X (%04X)\n", port, z80_get_reg (Z80_PC));
#endif
  return 0xFF;
}

void cpu_writeport16(unsigned int port, unsigned int data)
{
#if LOG_PORT
    error("Z80 write %02X to port %04X (%04X)\n", data, port, z80_get_reg(Z80_PC));
#endif
}


/*
    Handlers for access to unused addresses and those which make the
    machine lock up.
*/
void z80_unused_w(int address, int data)
{
    error("Z80 unused write %04X = %02X (%04X)\n", address, data, z80_get_reg(Z80_PC));    
}

int z80_unused_r(int address)
{
	error ("Z80 unused read %04X (%04X)\n", address, z80_get_reg (Z80_PC));
	return 0xFF;
}

void z80_lockup_w(int address, int data)
{
	error("Z80 lockup write %04X = %02X (%04X)\n", address, data, z80_get_reg(Z80_PC));    
	gen_running = 0;
	z80_end_timeslice ();
}

int z80_lockup_r(int address)
{
	error ("Z80 lockup read %04X (%04X)\n", address, z80_get_reg (Z80_PC));
	gen_running = 0;
	z80_end_timeslice ();
	return 0xFF;
}