theglob.c

这个是延伸mame的在wince平台下的游戏模拟器的代码

/***************************************************************************

  machine.c

  Functions to emulate general aspects of the machine (RAM, ROM, interrupts,
  I/O ports)

  The Glob protection description:

  The Glob is designed to run on modified Pacman hardware.  It contains
  two graphics ROMs at 5E and 5F, but contains code ROMs on a daughterboard
  similar in concept to Ms. Pacman.  However, these code ROMs are decrypted
  through additional circuitry.  The daughterboard was encased in epoxy.

  Here's a description of the protection as best as I can give it.

  1)  The decrypted D0 bit fed to the CPU is simply an inversion of the
      D5 bit from the code ROMs.
  2)  The decrypted D1 bit fed to the CPU is simply an inversion of the
      D2 bit from the code ROMs.
  3)  The other 6 data bits are decrypted by a 10H8 PAL.  The PAL also
      takes as input a 4-bit counter.  The counter is incremented and
	  decremented as follows:
	  - the Z-80 command IN($xx) where xx is an odd number decrements the
	    counter; an even number increments the counter.
		Ex:  IN($64) would increment the counter, IN($6B) would decrement
		the counter.
  4)  The PAL output also contains the two ROM enable lines used to enable
      the two encrypted code ROMs.  As long as the system is working
	  correctly, these ROMs will always be enabled.

  As it so happens, only four counter values are ever used, which is
  fortunate because the PAL only contains signals to enable the ROMs for
  those four counter values.  The valid counter values are $8, $9, $A, and
  $B.  The counter's intial value is $A, which is set by jumpers on the
  daughterboard.  Following is a description of the resulting decryptions
  for these four counter states.

  COUNTER		ENCRYPTED	DECRYPTED
				  VALUE	      VALUE

				DDDDDDDD	DDDDDDDD
				76543210	76543210

  Counter = 8:  abcdefgh	EAhBDgFC
  Counter = 9:	abcdefgh	FAgeDBFC
  Counter = A:	abcdefgh	EHDBagFC
  Counter = B:  abcdefgh	GHDEaBFC

  In the above diagram, capital letters represent inverted bits.  Notice
  that bits D2 and D5 are the same independent of counter state, this is
  because these bits are not decrypted by the PAL.


  In the code below, all four of these decryption patterns are used to
  decrypt the entire code ROMs before execution.  This is done for speed,
  since we can then just bankswitch between the decrypted code sets on
  each IN($xx) command, as opposed to dynamically decrypting every byte.

  - Mike Balfour ([e-mail])

***************************************************************************/

#include "driver.h"

void pacman_init_machine(void);

unsigned char *theglob_mem_rom;

static int counter=0;


static void theglob_decrypt_rom_8(void)
{
	int oldbyte,inverted_oldbyte,newbyte;
	int mem;
	unsigned char *RAM;

	RAM = Machine->memory_region[0];


	for (mem=0;mem<0x4000;mem++)
	{
		oldbyte = RAM[mem];
		inverted_oldbyte = ~oldbyte;

		/*	Note: D2 is inverted and connected to D1, D5 is inverted and
			connected to D0.  The other six data bits are converted by a
			PAL10H8 driven by the counter. */
		newbyte = 0;

		/* Direct inversion */
		newbyte  = (inverted_oldbyte & 0x04) >> 1;
		newbyte |= (inverted_oldbyte & 0x20) >> 5;
		/* PAL */
		newbyte |= (oldbyte & 0x01) << 5;
		newbyte |= (oldbyte & 0x02) << 1;
		newbyte |= (inverted_oldbyte & 0x08) << 4;
		newbyte |= (inverted_oldbyte & 0x10) >> 1;
		newbyte |= (inverted_oldbyte & 0x40) >> 2;
		newbyte |= (inverted_oldbyte & 0x80) >> 1;

		RAM[mem + 0x10000] = newbyte;
	}

	return;
}


static void theglob_decrypt_rom_9(void)
{
	int oldbyte,inverted_oldbyte,newbyte;
	int mem;
	unsigned char *RAM;

	RAM = Machine->memory_region[0];

	for (mem=0;mem<0x4000;mem++)
	{
		oldbyte = RAM[mem];
		inverted_oldbyte = ~oldbyte;

		/*	Note: D2 is inverted and connected to D1, D5 is inverted and
			connected to D0.  The other six data bits are converted by a
			PAL10H8 driven by the counter. */
		newbyte = 0;

		/* Direct inversion */
		newbyte  = (inverted_oldbyte & 0x04) >> 1;
		newbyte |= (inverted_oldbyte & 0x20) >> 5;
		/* PAL */
		newbyte |= (oldbyte & 0x01) << 5;
		newbyte |= (inverted_oldbyte & 0x02) << 6;
		newbyte |= (oldbyte & 0x08) << 1;
		newbyte |= (inverted_oldbyte & 0x10) >> 1;
		newbyte |= (inverted_oldbyte & 0x40) >> 4;
		newbyte |= (inverted_oldbyte & 0x80) >> 1;

		RAM[mem + 0x14000] = newbyte;
	}

	return;
}

static void theglob_decrypt_rom_A(void)
{
	int oldbyte,inverted_oldbyte,newbyte;
	int mem;
	unsigned char *RAM;

	RAM = Machine->memory_region[0];

	for (mem=0;mem<0x4000;mem++)
	{
		oldbyte = RAM[mem];
		inverted_oldbyte = ~oldbyte;

		/*	Note: D2 is inverted and connected to D1, D5 is inverted and
			connected to D0.  The other six data bits are converted by a
			PAL10H8 driven by the counter. */
		newbyte = 0;

		/* Direct inversion */
		newbyte  = (inverted_oldbyte & 0x04) >> 1;
		newbyte |= (inverted_oldbyte & 0x20) >> 5;
		/* PAL */
		newbyte |= (inverted_oldbyte & 0x01) << 6;
		newbyte |= (oldbyte & 0x02) << 1;
		newbyte |= (inverted_oldbyte & 0x08) << 4;
		newbyte |= (inverted_oldbyte & 0x10) << 1;
		newbyte |= (inverted_oldbyte & 0x40) >> 2;
		newbyte |= (oldbyte & 0x80) >> 4;

		RAM[mem + 0x18000] = newbyte;
	}

	return;
}

static void theglob_decrypt_rom_B(void)
{
	int oldbyte,inverted_oldbyte,newbyte;
	int mem;
	unsigned char *RAM;

	RAM = Machine->memory_region[0];

	for (mem=0;mem<0x4000;mem++)
	{
		oldbyte = RAM[mem];
		inverted_oldbyte = ~oldbyte;

		/*	Note: D2 is inverted and connected to D1, D5 is inverted and
			connected to D0.  The other six data bits are converted by a
			PAL10H8 driven by the counter. */
		newbyte = 0;

		/* Direct inversion */
		newbyte  = (inverted_oldbyte & 0x04) >> 1;
		newbyte |= (inverted_oldbyte & 0x20) >> 5;
		/* PAL */
		newbyte |= (inverted_oldbyte & 0x01) << 6;
		newbyte |= (inverted_oldbyte & 0x02) << 6;
		newbyte |= (oldbyte & 0x08) << 1;
		newbyte |= (inverted_oldbyte & 0x10) << 1;
		newbyte |= (inverted_oldbyte & 0x40) >> 4;
		newbyte |= (oldbyte & 0x80) >> 4;

		RAM[mem + 0x1C000] = newbyte;
	}

	return;
}


int theglob_decrypt_rom(int offset)
{
	unsigned char *RAM = Machine->memory_region[Machine->drv->cpu[0].memory_region];

	if (offset & 0x01)
	{
		counter = counter - 1;
		if (counter < 0)
			counter = 0x0F;
	}
	else
	{
		counter = (counter + 1) & 0x0F;
	}

	switch(counter)
	{
		case 0x08:	cpu_setbank (1, &RAM[0x10000]);		break;
		case 0x09:	cpu_setbank (1, &RAM[0x14000]);		break;
		case 0x0A:	cpu_setbank (1, &RAM[0x18000]);		break;
		case 0x0B:	cpu_setbank (1, &RAM[0x1C000]);		break;
		default:
			break;
	}

	return 0;
}


void theglob_init_machine(void)
{
	unsigned char *RAM = Machine->memory_region[Machine->drv->cpu[0].memory_region];

	/* While the PAL supports up to 16 decryption methods, only four
		are actually used in the PAL.  Therefore, we'll take a little
		memory overhead and decrypt the ROMs using each method in advance. */
	theglob_decrypt_rom_8();
	theglob_decrypt_rom_9();
	theglob_decrypt_rom_A();
	theglob_decrypt_rom_B();

	/* The initial state of the counter is 0x0A */
	counter = 0x0A;
	cpu_setbank (1, &RAM[0x18000]);

	pacman_init_machine();
}