// license:BSD-3-Clause
// copyright-holders:Morten Shearman Kirkegaard, Samuel Neves, Peter Wilhelmsen
/*************************************************************************
atarixga.cpp
Atari XGA encryption FPGAs
**************************************************************************
Part numbers:
136094-0072 Moto Frenzy
136095-0072 Space Lords
? Road Riot's Revenge
136094-0004A Primal Rage
? T-Mek
*************************************************************************/
#include "emu.h"
#include "atarixga.h"
/*************************************
*
* Decryption
*
*************************************/
static uint16_t ctz(uint16_t x)
{
uint16_t n = 0;
if (x == 0) return 16;
if (!(x & 0x00FF)) n += 8, x >>= 8;
if (!(x & 0x000F)) n += 4, x >>= 4;
if (!(x & 0x0003)) n += 2, x >>= 2;
if (!(x & 0x0001)) n += 1, x >>= 1;
return n;
}
static size_t popcount(uint16_t x)
{
size_t count = 0;
while (x != 0)
{
count += 1;
x &= x - 1;
}
return count;
}
static uint16_t parity(uint16_t x)
{
return popcount(x) & 1;
}
/*************************************
*
* 136094-0072 (Moto Frenzy)
*
*************************************/
DEFINE_DEVICE_TYPE(ATARI_136094_0072, atari_136094_0072_device, "136094_0072", "Atari 136094-0072 XGA")
atari_136094_0072_device::atari_136094_0072_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
: atari_xga_device(mconfig, ATARI_136094_0072, tag, owner, clock)
{
}
void atari_136094_0072_device::device_start()
{
m_ram = std::make_unique<uint16_t[]>(RAM_WORDS);
save_pointer(NAME(m_ram), RAM_WORDS * sizeof(uint16_t));
save_item(NAME(m_address));
save_item(NAME(m_ciphertext));
}
void atari_136094_0072_device::device_reset()
{
memset(m_ram.get(), 0, RAM_WORDS * sizeof(uint16_t));
m_mode = FPGA_RESET;
m_address = 0;
m_ciphertext = 0;
}
uint16_t atari_136094_0072_device::lfsr1(uint16_t x)
{
const uint16_t bit = parity(x & 0x8016);
return (x << 1) | bit;
}
uint16_t atari_136094_0072_device::lfsr2(uint16_t x)
{
uint16_t bit = parity(x & 0x002D);
return (x >> 1) | (bit << 15);
}
uint16_t atari_136094_0072_device::powers2(uint8_t k, uint16_t x)
{
static const uint16_t L[16] =
{
0x5E85,0xBD0B,0x2493,0x17A3,
0x2F47,0x0005,0x000B,0x0017,
0x002F,0x005E,0x00BD,0x017A,
0x02F4,0x05E8,0x0BD0,0x17A1
};
uint16_t t = (x == 16) ? (L[4] ^ L[5]) : L[x];
for (size_t i = 0; i < k; ++i)
t = lfsr1(t);
return t;
}
uint16_t atari_136094_0072_device::decipher(uint8_t k, uint16_t c)
{
/* key 0x10 is special, it has 15 "identical twins". */
static const uint8_t kmap[128] =
{
0x6B,0x11,0x1B,0x19,0x4B,0x50,0x17,0x09,
0x5D,0x69,0x43,0x33,0x0F,0x0C,0x28,0x3F,
0x00,0x20,0x15,0x3C,0x57,0x38,0x00,0x07,
0x49,0x25,0x61,0x2F,0x2B,0x4E,0x64,0x00,
0x45,0x41,0x6D,0x52,0x31,0x66,0x22,0x59,
0x00,0x70,0x6F,0x5B,0x46,0x6E,0x67,0x5A,
0x26,0x30,0x2C,0x65,0x21,0x3D,0x58,0x00,
0x5E,0x44,0x0D,0x40,0x6C,0x1C,0x51,0x0A,
0x35,0x2A,0x13,0x4D,0x63,0x00,0x00,0x3A,
0x00,0x48,0x54,0x24,0x60,0x1E,0x2E,0x01,
0x56,0x03,0x37,0x00,0x04,0x00,0x05,0x06,
0x00,0x55,0x1F,0x02,0x36,0x14,0x00,0x3B,
0x5F,0x0E,0x1D,0x0B,0x27,0x2D,0x3E,0x00,
0x00,0x5C,0x47,0x68,0x42,0x53,0x32,0x23,
0x4A,0x62,0x4F,0x00,0x00,0x16,0x39,0x08,
0x6A,0x34,0x10,0x29,0x12,0x1A,0x4C,0x18
};
uint16_t p = 0;
/* Only 128 keys internally, if high bit set,
then find the 7-bit "twin" by xor 0xA8. */
if (k & 0x80)
k ^= 0xA8;
k = kmap[k];
if ((c & (c - 1)) == 0)
return powers2(k, ctz(c));
for (uint16_t bit = 0; bit < 5; ++bit)
{
if ((c >> bit) & 1)
{
p ^= powers2(k, bit);
}
}
for (uint16_t bit = 5; bit < 16; ++bit)
{
if ((c >> bit) & 1)
{
p ^= powers2(k, bit + 1);
}
}
uint16_t x = 0x8010;
for (uint16_t i = 0; i < k + 3; ++i)
{
if (x == c)
{
return (p == 1) ? 0 : lfsr2(p);
}
x = lfsr2(x);
}
return p;
}
/*************************************
*
* Write/Read access
*
*************************************/
void atari_136094_0072_device::write(offs_t offset, uint32_t data, uint32_t mem_mask)
{
switch (m_mode)
{
case FPGA_RESET:
return;
case FPGA_SETKEY:
/* Write table to FPGA SRAM. */
if (ACCESSING_BITS_16_31)
m_ram[offset << 1] = uint16_t (data >> 16);
if (ACCESSING_BITS_0_15)
m_ram[(offset << 1) + 1] = uint16_t(data & 0xFFFF);
break;
case FPGA_DECIPHER:
/* Send Ciphertext to FPGA for decryption. */
if (ACCESSING_BITS_16_31)
{
m_address = offset << 2;
m_ciphertext = uint16_t(data >> 16);
}
if (ACCESSING_BITS_0_15)
{
m_address = (offset << 2) + 2;
m_ciphertext = uint16_t(data & 0xFFFF);
}
break;
}
}
uint32_t atari_136094_0072_device::read(offs_t offset, uint32_t mem_mask)
{
switch (offset << 2)
{
case 0x0FC0:
m_mode = FPGA_RESET;
break;
case 0x0010:
m_mode = FPGA_SETKEY;
break;
case 0x0020:
m_mode = FPGA_DECIPHER;
break;
}
if (m_mode == FPGA_RESET)
return 0;
uint32_t plaintext = 0;
if (m_mode == FPGA_DECIPHER)
{
uint16_t address = (offset << 2) - 0x400;
if (ACCESSING_BITS_0_15)
address += 2;
/* Reply with decrypted plaintext */
if (address == m_address)
{
uint16_t key_offset, key_byte;
/* Algorithm to select key byte based on offset. */
key_offset = ((((address >> 4) & 1) ^ 1) << 0)
^ ((((address >> 2) & 1) ^ 0) << 1)
^ ((((address >> 8) & 1) ^ 0) << 2)
^ ((((address >> 3) & 1) ^ 1) << 3)
^ ((((address >> 1) & 1) ^ 1) << 4)
^ ((((address >> 6) & 1) ^ 0) << 5)
^ ((((address >> 7) & 1) ^ 0) << 6)
^ ((((address >> 5) & 1) ^ 1) << 7)
^ ((((address >> 9) & 1) ^ 0) << 8)
^ ((((address >> 10) & 1) ^ 0) << 9);
key_byte = m_ram[key_offset];
/* And now for the full magic. */
plaintext = decipher(key_byte, m_ciphertext);
if (ACCESSING_BITS_16_31)
plaintext <<= 16;
}
}
return plaintext;
}
/*************************************
*
* 136095-0072 (Space Lords)
*
*************************************/
DEFINE_DEVICE_TYPE(ATARI_136095_0072, atari_136095_0072_device, "136095_0072", "Atari 136095-0072 XGA")
atari_136095_0072_device::atari_136095_0072_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
: atari_xga_device(mconfig, ATARI_136095_0072, tag, owner, clock)
{
}
void atari_136095_0072_device::device_start()
{
m_ram = std::make_unique<uint16_t[]>(RAM_WORDS);
save_pointer(NAME(m_ram), RAM_WORDS * sizeof(uint16_t));
save_item(NAME(m_update.addr));
save_item(NAME(m_update.data));
save_item(NAME(m_poly_lsb));
save_item(NAME(m_reply));
}
void atari_136095_0072_device::device_reset()
{
memset(m_ram.get(), 0, RAM_WORDS * sizeof(uint16_t));
}
uint16_t atari_136095_0072_device::lfsr1(uint16_t x)
{
uint16_t bit = parity(x & (0xC100 | m_poly_lsb));
return (x << 1) | bit;
}
uint16_t atari_136095_0072_device::lfsr2(uint16_t x)
{
uint16_t bit = parity(x & (0x8201 | (m_poly_lsb << 1)));
return (x >> 1) | (bit << 15);
}
uint16_t atari_136095_0072_device::powers2(uint8_t k, uint16_t x)
{
size_t i, n;
uint16_t t = 1 << (x % 16);
if ((x == 15) || (x == 16))
n = k + 13;
else
n = k + 14;
for (i = 0; i < n; ++i)
t = lfsr1(t);
return t;
};
uint16_t atari_136095_0072_device::decipher(uint8_t k, uint16_t c)
{
uint16_t i, p = 0;
/* key 0x00 is special, it has 15 "identical twins". */
static const uint8_t kmap[128] =
{
0x00,0x3C,0x0D,0x0B,0x5E,0x09,0x2A,0x31,
0x00,0x56,0x11,0x4D,0x14,0x34,0x3A,0x44,
0x24,0x41,0x51,0x28,0x1E,0x2F,0x68,0x00,
0x5C,0x49,0x18,0x04,0x37,0x00,0x07,0x6B,
0x58,0x46,0x0F,0x60,0x4B,0x6D,0x53,0x20,
0x00,0x70,0x62,0x6F,0x59,0x61,0x6E,0x54,
0x4A,0x19,0x38,0x6C,0x42,0x52,0x1F,0x01,
0x57,0x12,0x15,0x45,0x3D,0x0E,0x5F,0x32,
0x4F,0x36,0x00,0x2C,0x06,0x00,0x26,0x6A,
0x64,0x5B,0x48,0x22,0x17,0x3F,0x1B,0x03,
0x66,0x1D,0x2E,0x00,0x67,0x00,0x00,0x00,
0x65,0x23,0x40,0x1C,0x50,0x2D,0x00,0x27,
0x13,0x16,0x3E,0x33,0x1A,0x39,0x43,0x02,
0x00,0x63,0x5A,0x55,0x47,0x10,0x4C,0x21,
0x5D,0x05,0x00,0x08,0x25,0x29,0x30,0x69,
0x00,0x4E,0x35,0x3B,0x00,0x0C,0x0A,0x2B,
};
/* Only 128 keys internally, if high bit set,
then find the 7-bit "twin" by xor 0xA8. */
if (k & 0x80) k ^= 0xA8;
k = kmap[k];
if ((c & (c - 1)) == 0) {
return powers2(k, ctz(c));
}
for (i = 0; i < 15; ++i) {
if (1 & (c >> i)) {
p ^= powers2(k, i);
}
}
if (c & 0x8000) {
p ^= powers2(k, 16);
}
uint16_t x = 0xC000;
for (i = 0; i < k + 13; ++i)
{
if (x == c)
return (p == 1) ? 0 : lfsr2(p);
x = lfsr2(x);
}
return p;
}
void atari_136095_0072_device::polylsb_write(offs_t offset, uint32_t data)
{
m_update.addr = offset;
m_update.data[offset] = data;
}
uint32_t atari_136095_0072_device::polylsb_read(offs_t offset, uint32_t mem_mask)
{
if (m_update.addr == offset)
{
if (ACCESSING_BITS_16_31)
{
m_poly_lsb = (m_update.data[offset] >> 16) & 0xFF;
}
else
{
m_poly_lsb = m_update.data[offset] & 0xFF;
}
}
return m_update.data[offset];
}
void atari_136095_0072_device::write(offs_t offset, uint32_t data, uint32_t mem_mask)
{
uint16_t address, value = 0;
address = offset << 2;
if (ACCESSING_BITS_16_31)
{
value = uint16_t (data >> 16);
}
if (ACCESSING_BITS_0_15)
{
address += 2;
value = uint16_t (data & 0xFFFF);
}
switch (m_mode)
{
case FPGA_SETKEY:
/* Write table to FPGA SRAM. */
if (ACCESSING_BITS_16_31)
{
m_ram[offset << 1] = value;
}
if (ACCESSING_BITS_0_15)
{
m_ram[(offset << 1) + 1] = value;
}
break;
/* Send Ciphertext to FPGA for decryption. */
case FPGA_DECIPHER:
uint16_t key_offset, key_byte;
/* Algorithm to select key byte based on offset. */
key_offset = ((((address >> 8) & 1) ^ 1) << 0)
| ((((address >> 2) & 1) ^ 1) << 1)
| ((((address >> 7) & 1) ^ 0) << 2)
| ((((address >> 1) & 1) ^ 0) << 3)
| ((((address >> 4) & 1) ^ 1) << 4)
| ((((address >> 5) & 1) ^ 1) << 5)
| ((((address >> 3) & 1) ^ 0) << 6)
| ((((address >> 6) & 1) ^ 1) << 7)
| ((((address >> 9) & 1) ^ 0) << 8)
| ((((address >> 10) & 1) ^ 0) << 9)
| ((((address >> 11) & 1) ^ 0) << 10)
| ((((address >> 12) & 1) ^ 0) << 11);
key_byte = m_ram[key_offset];
m_reply = decipher(key_byte, value);
break;
case FPGA_PROCESS:
case FPGA_RESULT:
default:
break;
}
}
uint32_t atari_136095_0072_device::read(offs_t offset, uint32_t mem_mask)
{
uint16_t address;
uint32_t reply = 0;
address = offset << 2;
if (ACCESSING_BITS_0_15)
address += 2;
switch (address)
{
case 0x0020:
m_mode = FPGA_SETKEY;
break;
case 0x0042:
m_mode = FPGA_DECIPHER;
break;
case 0x0C00:
m_mode = FPGA_PROCESS;
reply = -1;
break;
case 0x0FC0:
m_mode = FPGA_RESULT;
reply = m_reply << 16;
break;
default:
break;
}
return reply;
}