diff options
Diffstat (limited to 'src/mame/machine/m6502_swap_op_d2_d7.cpp')
-rw-r--r-- | src/mame/machine/m6502_swap_op_d2_d7.cpp | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/src/mame/machine/m6502_swap_op_d2_d7.cpp b/src/mame/machine/m6502_swap_op_d2_d7.cpp new file mode 100644 index 00000000000..eab70e43d93 --- /dev/null +++ b/src/mame/machine/m6502_swap_op_d2_d7.cpp @@ -0,0 +1,69 @@ +// license:BSD-3-Clause +// copyright-holders:David Shah, David Haywood +/*************************************************************************** + + m6502_swap_op_d2_d7.cpp + + 6502 with instruction scrambling + + This form of scrambling is used in the VRT VT1682 + (it's used for the MiWi2 and InterAct consoles). + + This is simpler, permanently activated and consists of swapping opcode bits + 7 and 2. + +***************************************************************************/ + +#include "emu.h" +#include "m6502_swap_op_d2_d7.h" + +DEFINE_DEVICE_TYPE(M6502_SWAP_OP_D2_D7, m6502_swap_op_d2_d7, "m6502_swap_op_d2_d7", "M6502 swapped D2/D7") + +m6502_swap_op_d2_d7::m6502_swap_op_d2_d7(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock) : + m6502_device(mconfig, M6502_SWAP_OP_D2_D7, tag, owner, clock) +{ +} + +void m6502_swap_op_d2_d7::device_start() +{ + mintf = std::make_unique<mi_decrypt>(); + init(); +} + +void m6502_swap_op_d2_d7::device_reset() +{ + m6502_device::device_reset(); +} + +uint8_t m6502_swap_op_d2_d7::mi_decrypt::descramble(uint8_t op) +{ + return bitswap<8>(op, 2, 6, 5, 4, 3, 7, 1, 0); +} + +uint8_t m6502_swap_op_d2_d7::mi_decrypt::read_sync(uint16_t adr) +{ + uint8_t res = cache->read_byte(adr); + + res = descramble(res); + + return res; +} + +std::unique_ptr<util::disasm_interface> m6502_swap_op_d2_d7::create_disassembler() +{ + return std::make_unique<disassembler>(downcast<mi_decrypt *>(mintf.get())); +} + +m6502_swap_op_d2_d7::disassembler::disassembler(mi_decrypt *mi) : mintf(mi) +{ +} + +u32 m6502_swap_op_d2_d7::disassembler::interface_flags() const +{ + return SPLIT_DECRYPTION; +} + +u8 m6502_swap_op_d2_d7::disassembler::decrypt8(u8 value, offs_t pc, bool opcode) const +{ + return opcode ? mintf->descramble(value) : value; +} |