diff options
Diffstat (limited to 'src/mame/machine')
-rw-r--r-- | src/mame/machine/atarixga.cpp | 299 | ||||
-rw-r--r-- | src/mame/machine/atarixga.h | 54 |
2 files changed, 353 insertions, 0 deletions
diff --git a/src/mame/machine/atarixga.cpp b/src/mame/machine/atarixga.cpp new file mode 100644 index 00000000000..ac423c9c641 --- /dev/null +++ b/src/mame/machine/atarixga.cpp @@ -0,0 +1,299 @@ +// license:BSD-3-Clause +// copyright-holders:Morten Shearman Kirkegaard, Samuel Neves, Peter Wilhelmsen +/************************************************************************* + + atarixga.cpp + + Atari XGA encryption FPGA + + ************************************************************************** + + Part numbers: + + 136094-0072 Moto Frenzy + 136095-0072 Space Lords + ? Road Riot's Revenge + 136094-0004A Primal Rage + ? T-Mek + +*************************************************************************/ + +#include "atarixga.h" + + +extern const device_type ATARI_XGA = &device_creator<atari_xga_device>; + +atari_xga_device::atari_xga_device(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock) +: device_t(mconfig, ATARI_XGA, "Atari XGA", tag, owner, clock, "xga", __FILE__), + m_mode(FPGA_RESET), + m_address(0), + m_ciphertext(0) +{ +} + + + +/************************************* + * + * Initialization + * + *************************************/ + +void atari_xga_device::device_start() +{ + m_ram = std::make_unique<UINT16[]>(RAM_WORDS); + + save_pointer(NAME(m_ram.get()), RAM_WORDS * sizeof(UINT16)); + save_item(NAME(m_address)); + save_item(NAME(m_ciphertext)); +} + +void atari_xga_device::device_reset() +{ + memset(m_ram.get(), 0, RAM_WORDS * sizeof(UINT16)); + m_mode = FPGA_RESET; + m_address = 0; + m_ciphertext = 0; +} + + + +/************************************* + * + * Definitions + * + *************************************/ + +// TODO: Add definitions for other games +// Moto Frenzy + +/* key 0x10 is special, it has 15 "identical twins". */ +static const UINT8 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 +}; + + + +/************************************* + * + * Decryption + * + *************************************/ + +UINT16 atari_xga_device::ctz(UINT16 x) +{ + UINT16 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; +} + +size_t atari_xga_device::popcount(UINT16 x) +{ + size_t count = 0; + while (x != 0) + { + count += 1; + x &= x - 1; + } + return count; +} + +UINT16 atari_xga_device::parity(UINT16 x) +{ + return popcount(x) & 1; +} + +UINT16 atari_xga_device::lfsr1(UINT16 x) +{ + UINT16 bit = parity(x & 0x8016); + return (x << 1) | bit; +} + +UINT16 atari_xga_device::lfsr2(UINT16 x) +{ + UINT16 bit = parity(x & 0x002D); + return (x >> 1) | (bit << 15); +} + +UINT16 atari_xga_device::powers2(UINT8 k, UINT16 x) +{ + static const UINT16 L[16] = + { + 0x5E85,0xBD0B,0x2493,0x17A3, + 0x2F47,0x0005,0x000B,0x0017, + 0x002F,0x005E,0x00BD,0x017A, + 0x02F4,0x05E8,0x0BD0,0x17A1 + }; + + UINT16 t = (x == 16) ? (L[4] ^ L[5]) : L[x]; + + for (size_t i = 0; i < k; ++i) + { + t = lfsr1(t); + } + + return t; +} + +UINT16 atari_xga_device::decipher(UINT8 k, UINT16 c) +{ + UINT16 bit, i, 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 (bit = 0; bit < 5; ++bit) + { + if ((c >> bit) & 1) + { + p ^= powers2(k, bit); + } + } + + for (bit = 5; bit < 16; ++bit) + { + if ((c >> bit) & 1) + { + p ^= powers2(k, bit + 1); + } + } + + UINT16 x = 0x8010; + for (i = 0; i < k + 3; ++i) + { + if (x == c) + { + return (p == 1) ? 0 : lfsr2(p); + } + x = lfsr2(x); + } + + return p; +} + + + +/************************************* + * + * Write/Read access + * + *************************************/ + +WRITE32_MEMBER(atari_xga_device::write) +{ + 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 (data >> 16); + if (ACCESSING_BITS_0_15) + m_ram[(offset << 1) + 1] = UINT16(data & 0xFFFF); + + break; + + case FPGA_DECIPHER: + /* Send Ciphertext to FPGA for decryption. */ + if (ACCESSING_BITS_16_31) + { + m_address = offset << 2; + m_ciphertext = UINT16(data >> 16); + } + if (ACCESSING_BITS_0_15) + { + m_address = (offset << 2) + 2; + m_ciphertext = UINT16(data & 0xFFFF); + } + break; + } +} + +READ32_MEMBER(atari_xga_device::read) +{ + UINT32 plaintext = 0; + + 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; + } + + if (m_mode == FPGA_DECIPHER) + { + UINT16 address = (offset << 2) - 0x400; + + if (ACCESSING_BITS_0_15) + address += 2; + + /* Reply with decrypted plaintext */ + if (address == m_address) + { + UINT16 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; +} diff --git a/src/mame/machine/atarixga.h b/src/mame/machine/atarixga.h new file mode 100644 index 00000000000..710aedb22c2 --- /dev/null +++ b/src/mame/machine/atarixga.h @@ -0,0 +1,54 @@ +// license:BSD-3-Clause +// copyright-holders:Morten Shearman Kirkegaard, Samuel Neves, Peter Wilhelmsen +/************************************************************************* + + atarixga.h + + Atari XGA encryption FPGA + +*************************************************************************/ + +#ifndef __MACHINE_ATARIXGA__ +#define __MACHINE_ATARIXGA__ + +extern const device_type ATARI_XGA; + +class atari_xga_device : public device_t +{ +public: + // construction/destruction + atari_xga_device(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock); + + DECLARE_WRITE32_MEMBER(write); + DECLARE_READ32_MEMBER(read); + +protected: + virtual void device_start() override; + virtual void device_reset() override; + +private: + static const size_t RAM_WORDS = 2048; + + enum fpga_mode + { + FPGA_RESET, + FPGA_SETKEY, + FPGA_DECIPHER + }; + + UINT16 powers2(UINT8 k, UINT16 x); + UINT16 lfsr2(UINT16 x); + UINT16 lfsr1(UINT16 x); + UINT16 parity(UINT16 x); + size_t popcount(UINT16 x); + UINT16 ctz(UINT16 x); + UINT16 decipher(UINT8 k, UINT16 c); + + fpga_mode m_mode; + UINT16 m_address; // last written address + UINT16 m_ciphertext; // last written ciphertext + std::unique_ptr<UINT16[]> m_ram; // CY7C185-45PC, only 16-Kbit used +}; + + +#endif |