/***************************************************************************************
Drakton (c) 1984 Epos
decryption by Pierpaolo Prazzoli
based on decryptions of the other Epos games
For general documentation on how the encryption works, see machine/theglobp.c
****************************************************************************************/
#include "driver.h"
#include "includes/dkong.h"
static void drakton_decrypt_rom_8(void)
{
UINT8 oldbyte,newbyte;
UINT8 *ROM;
int mem;
ROM = memory_region(REGION_CPU1);
for (mem=0;mem<0x4000;mem++)
{
oldbyte = ROM[mem];
/* 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 = (oldbyte & 0x02) | (~oldbyte & ~0x02);
newbyte = BITSWAP8(newbyte,7,6,1,3,0,4,2,5);
ROM[mem + 0x10000] = newbyte;
}
}
static void drakton_decrypt_rom_9(void)
{
UINT8 oldbyte,newbyte;
UINT8 *ROM;
int mem;
ROM = memory_region(REGION_CPU1);
for (mem=0;mem<0x4000;mem++)
{
oldbyte = ROM[mem];
/* 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 = (oldbyte & 0x40) | (~oldbyte & ~0x40);
newbyte = BITSWAP8(newbyte,7,1,4,3,0,6,2,5);
ROM[mem + 0x14000] = newbyte;
}
}
static void drakton_decrypt_rom_A(void)
{
UINT8 oldbyte,newbyte;
UINT8 *ROM;
int mem;
ROM = memory_region(REGION_CPU1);
for (mem=0;mem<0x4000;mem++)
{
oldbyte = ROM[mem];
/* 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 = (oldbyte & 0x8a) | (~oldbyte & ~0x8a);
newbyte = BITSWAP8(newbyte,7,6,1,0,3,4,2,5);
ROM[mem + 0x18000] = newbyte;
}
}
static void drakton_decrypt_rom_B(void)
{
UINT8 oldbyte,newbyte;
UINT8 *ROM;
int mem;
ROM = memory_region(REGION_CPU1);
for (mem=0;mem<0x4000;mem++)
{
oldbyte = ROM[mem];
/* 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 = (oldbyte & 0xc8) | (~oldbyte & ~0xc8);
newbyte = BITSWAP8(newbyte,7,1,4,0,3,6,2,5);
ROM[mem + 0x1C000] = newbyte;
}
}
DRIVER_INIT( drakton )
{
/* 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. */
drakton_decrypt_rom_8();
drakton_decrypt_rom_9();
drakton_decrypt_rom_A();
drakton_decrypt_rom_B();
}