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◆ main openmsx / src / memory / RomHolyQuran2.cc
3.6 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
// Holy Qu'ran  cartridge
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//  It is like an ASCII 8KB, but using the 5000h, 5400h, 5800h and 5C00h
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//  addresses.
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//
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// This is very similar to RomHolyQuran, but this mapper type works with the
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// encrypted ROM content. Thanks to n_n for implementing it in meisei and
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// sharing his implementation with us (and pointing us to it).
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#include "RomHolyQuran2.hh"
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#include "MSXCPU.hh"
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#include "MSXException.hh"
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#include "enumerate.hh"
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#include "narrow.hh"
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#include "outer.hh"
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#include "serialize.hh"
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#include <algorithm>
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#include <array>
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namespace openmsx {
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// protection uses a simple rotation on databus, some lines inverted:
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//   out0 = ~in3   out1 =  in7   out2 = ~in5   out3 = ~in1
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//   out4 =  in0   out5 =  in4   out6 = ~in2   out7 =  in6
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static constexpr auto decryptLUT = [] {
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	std::array<byte, 256> result = {};
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	//for (auto [i, r] : enumerate(result)) { msvc bug
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	for (int i = 0; i < 256; ++i) {
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		result[i] = byte((((i << 4) & 0x50) |
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		                  ((i >> 3) & 0x05) |
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		                  ((i << 1) & 0xa0) |
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		                  ((i << 2) & 0x08) |
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		                  ((i >> 6) & 0x02)) ^ 0x4d);
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	}
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	return result;
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}();
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RomHolyQuran2::RomHolyQuran2(const DeviceConfig& config, Rom&& rom_)
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	: MSXRom(config, std::move(rom_))
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	, romBlocks(*this)
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{
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	if (rom.size() != 0x100000) { // 1MB
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		throw MSXException("Holy Quran ROM should be exactly 1MB in size");
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	}
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	reset(EmuTime::dummy());
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}
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void RomHolyQuran2::reset(EmuTime /*time*/)
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{
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	std::ranges::fill(bank, &rom[0]);
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	decrypt = false;
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}
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byte RomHolyQuran2::readMem(uint16_t address, EmuTime time)
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{
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	byte result = RomHolyQuran2::peekMem(address, time);
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	if (!decrypt) [[unlikely]] {
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		if (getCPU().isM1Cycle(address)) {
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			// start decryption when we start executing the rom
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			decrypt = true;
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		}
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	}
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	return result;
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}
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byte RomHolyQuran2::peekMem(uint16_t address, EmuTime /*time*/) const
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{
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	if ((0x4000 <= address) && (address < 0xc000)) {
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		unsigned b = (address - 0x4000) >> 13;
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		byte raw = bank[b][address & 0x1fff];
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		return decrypt ? decryptLUT[raw] : raw;
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	} else {
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		return 0xff;
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	}
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}
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void RomHolyQuran2::writeMem(uint16_t address, byte value, EmuTime /*time*/)
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{
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	// TODO are switch addresses mirrored?
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	if ((0x5000 <= address) && (address < 0x6000)) {
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		byte region = (address >> 10) & 3;
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		bank[region] = &rom[(value & 127) * 0x2000];
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	}
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}
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const byte* RomHolyQuran2::getReadCacheLine(uint16_t address) const
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{
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	if ((0x4000 <= address) && (address < 0xc000)) {
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		return nullptr;
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	} else {
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		return unmappedRead.data();
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	}
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}
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byte* RomHolyQuran2::getWriteCacheLine(uint16_t address)
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{
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	if ((0x5000 <= address) && (address < 0x6000)) {
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		return nullptr;
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	} else {
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		return unmappedWrite.data();
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	}
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}
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template<typename Archive>
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void RomHolyQuran2::serialize(Archive& ar, unsigned /*version*/)
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{
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	// skip MSXRom base class
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	ar.template serializeBase<MSXDevice>(*this);
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	std::array<unsigned, 4> bb;
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	if constexpr (Archive::IS_LOADER) {
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		ar.serialize("banks", bb);
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		for (auto [i, b] : enumerate(bb)) {
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			bank[i] = &rom[(b & 127) * 0x2000];
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		}
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	} else {
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		for (auto [i, b] : enumerate(bb)) {
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			b = narrow<unsigned>((bank[i] - &rom[0]) / 0x2000);
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		}
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		ar.serialize("banks", bb);
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	}
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	ar.serialize("decrypt", decrypt);
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}
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INSTANTIATE_SERIALIZE_METHODS(RomHolyQuran2);
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REGISTER_MSXDEVICE(RomHolyQuran2, "RomHolyQuran2");
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RomHolyQuran2::Blocks::Blocks(const RomHolyQuran2& device_)
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	: RomBlockDebuggableBase(device_)
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{
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}
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unsigned RomHolyQuran2::Blocks::readExt(unsigned address)
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{
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	if ((address < 0x4000) || (address >= 0xc000)) return unsigned(-1);
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	unsigned page = (address - 0x4000) / 0x2000;
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	auto& device = OUTER(RomHolyQuran2, romBlocks);
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	return narrow<unsigned>(device.bank[page] - &device.rom[0]) / 0x2000;
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}
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} // namespace openmsx