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◆ main openmsx / src / serial / MSXModem.cc
4.3 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
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#include "MSXModem.hh"
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#include "CacheLine.hh"
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#include "MSXException.hh"
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#include "serialize.hh"
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// See also
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// https://sourceforge.net/p/msxsyssrc/git/ci/master/tree/modem100/t600/t600-0.mac
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// for a disassembly of the code in the ROM. That disassembly source by A.
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// Zeilemaker is the technical source for this implementation.
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//
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// MSX-Modem seems to be specified here:
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// http://ngs.no.coocan.jp/doc/wiki.cgi/datapack?page=2%BE%CF+MSX+MODEM
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namespace openmsx {
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MSXModem::MSXModem(DeviceConfig& config)
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	: MSXDevice(config)
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	, rom(getName() + " ROM", "rom", config)
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	, sram(getName() + " SRAM", 0x2000, config)
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{
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	if (rom.size() != 0x10000) {
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		throw MSXException("ROM must be exactly 64kB in size!");
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	}
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	reset(EmuTime::dummy());
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}
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void MSXModem::reset(EmuTime /*time*/)
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{
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	bank = 0; // TODO: verify
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	selectedNCUreg = 0; // TODO: verify
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}
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void MSXModem::writeMem(uint16_t address, uint8_t value, EmuTime /*time*/)
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{
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	if (address == 0x7FC0) {
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		//   b2-b0 = ROM segment (4000H-5FFFH)
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		//   b3    = off hook
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		//   b4    = connect to modem
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		//   b5    = speaker
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		if (uint8_t newBank = value & 0b111; bank != newBank) {
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			bank = newBank;
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			invalidateDeviceRCache();
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			//std::cerr << "Changed bank to " << int(bank) << "\n";
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		}
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		 // other bits not implemented
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	} else if (address == 0x7F00) {
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		// TODO: write NCU data
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		// These registers are actually connected to the modem part... but faked here.
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		// NCU register 0, write
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		// NCU register 1, write
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		//   b7 = send break disabled
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		//   b3 = disable receiver
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		// NCU register 2, write
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		// NCU register 3, write
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		//   transmitter data
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		//std::cerr << "Wrote to NCU reg " << int(selectedNCUreg & 0b11) << ": " << int(value) << "\n";
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	} else if (address == 0x7F40) {
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		// select NCU register
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		selectedNCUreg = value;
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		// std::cerr << "Changed selected NCU reg to " << int(selectedNCUreg) << "\n";
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	} else if ((0x6000 <= address) && (address < 0x8000)) {
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		sram.write(address & 0x1FFF, value);
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	}
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}
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uint8_t* MSXModem::getWriteCacheLine(uint16_t address)
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{
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	if (address == (0x7FC0 & CacheLine::HIGH)) return nullptr;
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	if (address == (0x7F40 & CacheLine::HIGH)) return nullptr;
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	if (address == (0x7F00 & CacheLine::HIGH)) return nullptr;
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	if ((0x6000 <= address) && (address < 0x8000)) {
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		return nullptr;
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	}
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	return unmappedWrite.data();
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}
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uint8_t MSXModem::readMem(uint16_t address, EmuTime time)
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{
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	return peekMem(address, time);
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}
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uint8_t MSXModem::peekMem(uint16_t address, EmuTime /*time*/) const
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{
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	if (address == 0x7FC0) {
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		//  b0    = line polarity
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		//  b1    = line polarity
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		//  b2    = pulse/tone dail
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		return 0; // not implemented
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	} else if (address == 0x7F00) {
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		// read NCU register data
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		// These registers are actually connected to the modem part... but faked here.
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		// NCU register 0, read
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		//   b0 =
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		//   b1 =
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		//   b2 =
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		//   b3 = break detected
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		//   b4 = long loop detected
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		//   b6 =
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		//   b7 = dial tone detected
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		// NCU register 1, read
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		//   b3 = empty transmitter
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		//   b2 = data in receiver
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		//   b1 =
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		//   b0 =
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		// NCU register 2, read
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		//   not used
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		// NCU register 3, read
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		//   receiver data
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		static constexpr std::array<uint8_t, 4> ncuRegsRead = {0x00, 0x08, 0x00, 0x00}; // set "empty transmitter" so software starts up...
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		//std::cerr << "Reading from NCU reg " << int(selectedNCUreg & 0b11) << "\n";
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		return ncuRegsRead[selectedNCUreg & 0b11];
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	} else if ((0x4000 <= address) && (address < 0x6000)) {
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		return rom[bank * 0x2000 + (address & 0x1FFF)];
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	} else if ((0x6000 <= address) && (address < 0x8000)) {
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		return sram[address & 0x1FFF];
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	} else {
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		return 0xFF;
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	}
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}
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const uint8_t* MSXModem::getReadCacheLine(uint16_t address) const
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{
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	if (address == (0x7FC0 & CacheLine::HIGH)) return nullptr;
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	if (address == (0x7F00 & CacheLine::HIGH)) return nullptr;
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	if ((0x4000 <= address) && (address < 0x6000)) {
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		return &rom[bank * 0x2000 + (address & 0x1FFF)];
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	}
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	if ((0x6000 <= address) && (address < 0x8000)) {
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		return &sram[address & 0x1FFF];
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	}
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	return unmappedRead.data();
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}
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template<typename Archive>
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void MSXModem::serialize(Archive& ar, unsigned /*version*/)
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{
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	ar.template serializeBase<MSXDevice>(*this);
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	ar.serialize("SRAM", sram,
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		     "bank", bank,
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		     "selectedNCUreg", selectedNCUreg);
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}
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INSTANTIATE_SERIALIZE_METHODS(MSXModem);
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REGISTER_MSXDEVICE(MSXModem, "MSXModem");
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} // namespace openmsx