I8251.cc

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#include "I8251.hh"
#include "serialize.hh"
#include "unreachable.hh"
#include <cassert>
 
namespace openmsx {
 
static constexpr byte STAT_TXRDY   = 0x01;
static constexpr byte STAT_RXRDY   = 0x02;
static constexpr byte STAT_TXEMPTY = 0x04;
static constexpr byte STAT_PE      = 0x08;
static constexpr byte STAT_OE      = 0x10;
static constexpr byte STAT_FE      = 0x20;
static constexpr byte STAT_SYN_BRK = 0x40;
static constexpr byte STAT_DSR     = 0x80;
 
static constexpr byte MODE_BAUDRATE    = 0x03;
static constexpr byte MODE_SYNCHRONOUS = 0x00;
static constexpr byte MODE_RATE1       = 0x01;
static constexpr byte MODE_RATE16      = 0x02;
static constexpr byte MODE_RATE64      = 0x03;
static constexpr byte MODE_WORD_LENGTH  = 0x0C;
static constexpr byte MODE_5BIT        = 0x00;
static constexpr byte MODE_6BIT        = 0x04;
static constexpr byte MODE_7BIT        = 0x08;
static constexpr byte MODE_8BIT        = 0x0C;
static constexpr byte MODE_PARITY_EVEN = 0x10;
static constexpr byte MODE_PARITY_ODD  = 0x00;
static constexpr byte MODE_PARITEVEN   = 0x20;
static constexpr byte MODE_STOP_BITS   = 0xC0;
static constexpr byte MODE_STOP_INV    = 0x00;
static constexpr byte MODE_STOP_1      = 0x40;
static constexpr byte MODE_STOP_15     = 0x80;
static constexpr byte MODE_STOP_2      = 0xC0;
static constexpr byte MODE_SINGLE_SYNC = 0x80;
 
static constexpr byte CMD_TXEN    = 0x01;
static constexpr byte CMD_DTR     = 0x02;
static constexpr byte CMD_RXE     = 0x04;
static constexpr byte CMD_SBRK    = 0x08;
static constexpr byte CMD_RST_ERR = 0x10;
static constexpr byte CMD_RTS     = 0x20;
static constexpr byte CMD_RESET   = 0x40;
static constexpr byte CMD_HUNT    = 0x80;
 
 
I8251::I8251(Scheduler& scheduler, I8251Interface& interface_, EmuTime::param time)
        : syncRecv (scheduler)
        , syncTrans(scheduler)
        , interface(interface_), clock(scheduler)
{
        reset(time);
}
 
void I8251::reset(EmuTime::param time)
{
        // initialize these to avoid UMR on savestate
        //   TODO investigate correct initial state after reset
        charLength = 0;
        recvDataBits  = SerialDataInterface::DataBits::D8;
        recvStopBits  = SerialDataInterface::StopBits::S1;
        recvParityBit = SerialDataInterface::Parity::EVEN;
        recvParityEnabled = false;
        recvBuf = 0;
        recvReady = false;
        sendByte = 0;
        sendBuffer = 0;
        mode = 0;
        sync1 = sync2 = 0;
 
        status = STAT_TXRDY | STAT_TXEMPTY;
        command = 0xFF; // make sure all bits change
        writeCommand(0, time);
        cmdPhase = CmdPhase::MODE;
}
 
byte I8251::readIO(word port, EmuTime::param time)
{
        switch (port & 1) {
                case 0:  return readTrans(time);
                case 1:  return readStatus(time);
                default: UNREACHABLE;
        }
}
 
byte I8251::peekIO(word port, EmuTime::param /*time*/) const
{
        switch (port & 1) {
                case 0:  return recvBuf;
                case 1:  return status; // TODO peekStatus()
                default: UNREACHABLE;
        }
}
 
 
void I8251::writeIO(word port, byte value, EmuTime::param time)
{
        switch (port & 1) {
        case 0:
                writeTrans(value, time);
                break;
        case 1:
                switch (cmdPhase) {
                using enum CmdPhase;
                case MODE:
                        setMode(value);
                        if ((mode & MODE_BAUDRATE) == MODE_SYNCHRONOUS) {
                                cmdPhase = SYNC1;
                        } else {
                                cmdPhase = CMD;
                        }
                        break;
                case SYNC1:
                        sync1 = value;
                        if (mode & MODE_SINGLE_SYNC) {
                                cmdPhase = CMD;
                        } else {
                                cmdPhase = SYNC2;
                        }
                        break;
                case SYNC2:
                        sync2 = value;
                        cmdPhase = CMD;
                        break;
                case CMD:
                        if (value & CMD_RESET) {
                                cmdPhase = MODE;
                        } else {
                                writeCommand(value, time);
                        }
                        break;
                default:
                        UNREACHABLE;
                }
                break;
        default:
                UNREACHABLE;
        }
}
 
void I8251::setMode(byte newMode)
{
        mode = newMode;
 
        auto dataBits = [&] {
                switch (mode & MODE_WORD_LENGTH) {
                using enum SerialDataInterface::DataBits;
                case MODE_5BIT: return D5;
                case MODE_6BIT: return D6;
                case MODE_7BIT: return D7;
                case MODE_8BIT: return D8;
                default: UNREACHABLE;
                }
        }();
        interface.setDataBits(dataBits);
 
        auto stopBits = [&] {
                switch(mode & MODE_STOP_BITS) {
                using enum SerialDataInterface::StopBits;
                case MODE_STOP_INV: return INV;
                case MODE_STOP_1:   return S1;
                case MODE_STOP_15:  return S1_5;
                case MODE_STOP_2:   return S2;
                default: UNREACHABLE;
                }
        }();
        interface.setStopBits(stopBits);
 
        bool parityEnable = (mode & MODE_PARITY_EVEN) != 0;
        SerialDataInterface::Parity parity = (mode & MODE_PARITEVEN) ?
                SerialDataInterface::Parity::EVEN : SerialDataInterface::Parity::ODD;
        interface.setParityBit(parityEnable, parity);
 
        unsigned baudrate = [&] {
                switch (mode & MODE_BAUDRATE) {
                case MODE_SYNCHRONOUS: return 1;
                case MODE_RATE1:       return 1;
                case MODE_RATE16:      return 16;
                case MODE_RATE64:      return 64;
                default: UNREACHABLE;
                }
        }();
 
        charLength = (((2 * (1 + unsigned(dataBits) + (parityEnable ? 1 : 0))) +
                       unsigned(stopBits)) * baudrate) / 2;
}
 
void I8251::writeCommand(byte value, EmuTime::param time)
{
        byte oldCommand = command;
        command = value;
 
        // CMD_RESET, CMD_TXEN, CMD_RXE  handled in other routines
 
        interface.setRTS((command & CMD_RTS) != 0, time);
        interface.setDTR((command & CMD_DTR) != 0, time);
 
        if (!(command & CMD_TXEN)) {
                // disable transmitter
                syncTrans.removeSyncPoint();
                status |= STAT_TXRDY | STAT_TXEMPTY;
        }
        if (command & CMD_RST_ERR) {
                status &= ~(STAT_PE | STAT_OE | STAT_FE);
        }
        if (command & CMD_SBRK) {
                // TODO
        }
        if (command & CMD_HUNT) {
                // TODO
        }
 
        if ((command ^ oldCommand) & CMD_RXE) {
                if (command & CMD_RXE) {
                        // enable receiver
                        status &= ~(STAT_PE | STAT_OE | STAT_FE); // TODO
                        recvReady = true;
                } else {
                        // disable receiver
                        syncRecv.removeSyncPoint();
                        status &= ~(STAT_PE | STAT_OE | STAT_FE); // TODO
                        status &= ~STAT_RXRDY;
                }
                interface.signal(time);
        }
}
 
byte I8251::readStatus(EmuTime::param time)
{
        byte result = status;
        if (interface.getDSR(time)) {
                result |= STAT_DSR;
        }
        return result;
}
 
byte I8251::readTrans(EmuTime::param time)
{
        status &= ~STAT_RXRDY;
        interface.setRxRDY(false, time);
        return recvBuf;
}
 
void I8251::writeTrans(byte value, EmuTime::param time)
{
        if (!(command & CMD_TXEN)) {
                return;
        }
        if (status & STAT_TXEMPTY) {
                // not sending
                send(value, time);
        } else {
                sendBuffer = value;
                status &= ~STAT_TXRDY;
        }
}
 
void I8251::setParityBit(bool enable, Parity parity)
{
        recvParityEnabled = enable;
        recvParityBit = parity;
}
 
void I8251::recvByte(byte value, EmuTime::param time)
{
        // TODO STAT_PE / STAT_FE / STAT_SYN_BRK
        assert(recvReady && (command & CMD_RXE));
        if (status & STAT_RXRDY) {
                status |= STAT_OE;
        } else {
                recvBuf = value;
                status |= STAT_RXRDY;
                interface.setRxRDY(true, time);
        }
        recvReady = false;
        if (clock.isPeriodic()) {
                EmuTime next = time + (clock.getTotalDuration() * charLength);
                syncRecv.setSyncPoint(next);
        }
}
 
bool I8251::isRecvEnabled() const
{
        return (command & CMD_RXE) != 0;
}
 
void I8251::send(byte value, EmuTime::param time)
{
        status &= ~STAT_TXEMPTY;
        sendByte = value;
        if (clock.isPeriodic()) {
                EmuTime next = time + (clock.getTotalDuration() * charLength);
                syncTrans.setSyncPoint(next);
        }
}
 
void I8251::execRecv(EmuTime::param time)
{
        assert(command & CMD_RXE);
        recvReady = true;
        interface.signal(time);
}
 
void I8251::execTrans(EmuTime::param time)
{
        assert(!(status & STAT_TXEMPTY) && (command & CMD_TXEN));
 
        interface.recvByte(sendByte, time);
        if (status & STAT_TXRDY) {
                status |= STAT_TXEMPTY;
        } else {
                status |= STAT_TXRDY;
                send(sendBuffer, time);
        }
}
 
 
static constexpr std::initializer_list<enum_string<SerialDataInterface::DataBits>> dataBitsInfo = {
                { "5", SerialDataInterface::DataBits::D5 },
                { "6", SerialDataInterface::DataBits::D6 },
                { "7", SerialDataInterface::DataBits::D7 },
                { "8", SerialDataInterface::DataBits::D8 }
};
SERIALIZE_ENUM(SerialDataInterface::DataBits, dataBitsInfo);
 
static constexpr std::initializer_list<enum_string<SerialDataInterface::StopBits>> stopBitsInfo = {
        { "INVALID", SerialDataInterface::StopBits::INV },
        { "1",       SerialDataInterface::StopBits::S1   },
        { "1.5",     SerialDataInterface::StopBits::S1_5  },
        { "2",       SerialDataInterface::StopBits::S2   }
};
SERIALIZE_ENUM(SerialDataInterface::StopBits, stopBitsInfo);
 
static constexpr std::initializer_list<enum_string<SerialDataInterface::Parity>> parityBitInfo = {
        { "EVEN", SerialDataInterface::Parity::EVEN },
        { "ODD",  SerialDataInterface::Parity::ODD  }
};
SERIALIZE_ENUM(SerialDataInterface::Parity, parityBitInfo);
 
static constexpr std::initializer_list<enum_string<I8251::CmdPhase>> cmdFazeInfo = {
        { "MODE",  I8251::CmdPhase::MODE  },
        { "SYNC1", I8251::CmdPhase::SYNC1 },
        { "SYNC2", I8251::CmdPhase::SYNC2 },
        { "CMD",   I8251::CmdPhase::CMD   }
};
SERIALIZE_ENUM(I8251::CmdPhase, cmdFazeInfo);
 
// version 1: initial version
// version 2: removed 'userData' from Schedulable
template<typename Archive>
void I8251::serialize(Archive& ar, unsigned version)
{
        if (ar.versionAtLeast(version, 2)) {
                ar.serialize("syncRecv",  syncRecv,
                             "syncTrans", syncTrans);
        } else {
                Schedulable::restoreOld(ar, {&syncRecv, &syncTrans});
        }
        ar.serialize("clock",             clock,
                     "charLength",        charLength,
                     "recvDataBits",      recvDataBits,
                     "recvStopBits",      recvStopBits,
                     "recvParityBit",     recvParityBit,
                     "recvParityEnabled", recvParityEnabled,
                     "recvBuf",           recvBuf,
                     "recvReady",         recvReady,
                     "sendByte",          sendByte,
                     "sendBuffer",        sendBuffer,
                     "status",            status,
                     "command",           command,
                     "mode",              mode,
                     "sync1",             sync1,
                     "sync2",             sync2,
                     "cmdFaze",           cmdPhase); // TODO fix spelling error if we ever need to upgrade this savestate format
}
INSTANTIATE_SERIALIZE_METHODS(I8251);
 
} // namespace openmsx