WinComm/drv/commdrv.c

// commdrv.c - High-speed COMM.DRV replacement
//
// All exported COMM.DRV functions, ring buffer management, port
// initialization, 16550 FIFO detection, and flow control.
//
// Drop-in replacement for Windows 3.1 stock COMM.DRV with proper
// FIFO management for reliable operation at 57600 and 115200 baud.

#include "commdrv.h"
#include <dos.h>
#include <string.h>

// -----------------------------------------------------------------------
// Debug logging via OutputDebugString
// -----------------------------------------------------------------------
#define DBG_ENABLED 0

#if DBG_ENABLED
static void dbgStr(const char FAR *msg)
{
    OutputDebugString(msg);
}

// Log a label and a 16-bit hex value: "label: 0xNNNN\r\n"
static void dbgHex16(const char FAR *label, uint16_t val)
{
    static const char hex[] = "0123456789ABCDEF";
    char buf[48];
    int  i;

    for (i = 0; i < 40 && label[i]; i++) {
        buf[i] = label[i];
    }
    buf[i++] = ':';
    buf[i++] = ' ';
    buf[i++] = '0';
    buf[i++] = 'x';
    buf[i++] = hex[(val >> 12) & 0xF];
    buf[i++] = hex[(val >> 8) & 0xF];
    buf[i++] = hex[(val >> 4) & 0xF];
    buf[i++] = hex[val & 0xF];
    buf[i++] = '\r';
    buf[i++] = '\n';
    buf[i]   = '\0';
    OutputDebugString(buf);
}

// Log a label and a signed 16-bit value: "label: -NNNN\r\n"
static void dbgInt16(const char FAR *label, int16_t val)
{
    char     buf[48];
    int      i;
    uint16_t uv;

    for (i = 0; i < 40 && label[i]; i++) {
        buf[i] = label[i];
    }
    buf[i++] = ':';
    buf[i++] = ' ';

    if (val < 0) {
        buf[i++] = '-';
        uv = (uint16_t)(-(int)val);
    } else {
        uv = (uint16_t)val;
    }

    // Print decimal (up to 5 digits)
    {
        char digits[6];
        int  n = 0;
        do {
            digits[n++] = (char)('0' + (uv % 10));
            uv /= 10;
        } while (uv > 0);
        while (n > 0) {
            buf[i++] = digits[--n];
        }
    }

    buf[i++] = '\r';
    buf[i++] = '\n';
    buf[i]   = '\0';
    OutputDebugString(buf);
}

// Log a FAR pointer as "label: SSSS:OOOO\r\n"
static void dbgFarPtr(const char FAR *label, void FAR *ptr)
{
    static const char hex[] = "0123456789ABCDEF";
    char     buf[48];
    int      i;
    uint16_t seg;
    uint16_t off;

    seg = _FP_SEG(ptr);
    off = _FP_OFF(ptr);

    for (i = 0; i < 32 && label[i]; i++) {
        buf[i] = label[i];
    }
    buf[i++] = ':';
    buf[i++] = ' ';
    buf[i++] = hex[(seg >> 12) & 0xF];
    buf[i++] = hex[(seg >> 8) & 0xF];
    buf[i++] = hex[(seg >> 4) & 0xF];
    buf[i++] = hex[seg & 0xF];
    buf[i++] = ':';
    buf[i++] = hex[(off >> 12) & 0xF];
    buf[i++] = hex[(off >> 8) & 0xF];
    buf[i++] = hex[(off >> 4) & 0xF];
    buf[i++] = hex[off & 0xF];
    buf[i++] = '\r';
    buf[i++] = '\n';
    buf[i]   = '\0';
    OutputDebugString(buf);
}

// Hex dump first 'count' bytes at a FAR pointer
static void dbgDump(const char FAR *label, void FAR *ptr, int count)
{
    static const char hex[] = "0123456789ABCDEF";
    char              buf[80];
    uint8_t FAR      *p;
    int               i;
    int               bi;

    p = (uint8_t FAR *)ptr;

    // Print label
    for (bi = 0; bi < 32 && label[bi]; bi++) {
        buf[bi] = label[bi];
    }
    buf[bi++] = ':';
    buf[bi++] = ' ';

    for (i = 0; i < count && bi < 70; i++) {
        buf[bi++] = hex[(p[i] >> 4) & 0xF];
        buf[bi++] = hex[p[i] & 0xF];
        buf[bi++] = ' ';
    }
    buf[bi++] = '\r';
    buf[bi++] = '\n';
    buf[bi]   = '\0';
    OutputDebugString(buf);
}
#else
#define dbgStr(msg)          ((void)0)
#define dbgHex16(label, val) ((void)0)
#define dbgInt16(label, val) ((void)0)
#define dbgFarPtr(label, p)  ((void)0)
#define dbgDump(l, p, n)     ((void)0)
#endif

// -----------------------------------------------------------------------
// Prototypes
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export inicom(DCB FAR *dcb);
int16_t FAR PASCAL _export setcom(DCB FAR *dcb);
int16_t FAR PASCAL _export setque(int16_t commId, int16_t rxSize, int16_t txSize);
int16_t FAR PASCAL _export reccom(int16_t commId, void FAR *buf, int16_t len);
int16_t FAR PASCAL _export sndcom(int16_t commId, void FAR *buf, int16_t len);
int16_t FAR PASCAL _export ctx(int16_t commId, int16_t ch);
int16_t FAR PASCAL _export trmcom(int16_t commId);
int16_t FAR PASCAL _export stacom(int16_t commId, COMSTAT FAR *stat);
int32_t FAR PASCAL _export cevt(int16_t commId, int16_t evtMask);
uint16_t FAR PASCAL _export cevtget(int16_t commId, int16_t evtMask);
int16_t FAR PASCAL _export cextfcn(int16_t commId, int16_t func);
int16_t FAR PASCAL _export cflush(int16_t commId, int16_t queue);
int16_t FAR PASCAL _export csetbrk(int16_t commId);
int16_t FAR PASCAL _export cclrbrk(int16_t commId);
DCB FAR * FAR PASCAL _export getdcb(int16_t commId);
void    FAR PASCAL _export suspendOpenCommPorts(void);
void    FAR PASCAL _export reactivateOpenCommPorts(void);
int16_t FAR PASCAL _export commWriteString(int16_t commId, void FAR *buf, int16_t len);
int16_t FAR PASCAL _export readCommString(int16_t commId, void FAR *buf, int16_t len);
int16_t FAR PASCAL _export enableNotification(int16_t commId, HWND hwnd, int16_t rxThresh, int16_t txThresh);

int     FAR PASCAL _export commNotifyWndProc(void);
int     FAR PASCAL LibMain(HANDLE hInstance, WORD wDataSeg, WORD wHeapSize, LPSTR lpCmdLine);
int     FAR PASCAL _export WEP(int nParam);

void            applyBaudRate(PortStateT *port, uint16_t baud);
void            applyLineParams(PortStateT *port, uint8_t byteSize, uint8_t parity, uint8_t stopBits);
static uint32_t cbrToBaud(uint16_t cbr);
int16_t         detect16550(uint16_t baseAddr);
void            enableFifo(PortStateT *port);
static int16_t  freeBuffers(PortStateT *port);
static int16_t  initBuffers(PortStateT *port, uint16_t rxSz, uint16_t txSz);
static void     initPortState(PortStateT *port, int16_t commId);
void            primeTx(PortStateT *port);
static void     readPortConfig(int16_t commId, uint16_t FAR *baseAddr, uint8_t FAR *irq);
static uint16_t readSystemIni(const char FAR *section, const char FAR *key, uint16_t defVal);

// -----------------------------------------------------------------------
// Port base addresses and IRQ table
// -----------------------------------------------------------------------
static const uint16_t portBase[MAX_PORTS] = {
    COM1_BASE, COM2_BASE, COM3_BASE, COM4_BASE
};

static const uint8_t portIrq[MAX_PORTS] = {
    COM1_IRQ, COM2_IRQ, COM3_IRQ, COM4_IRQ
};

// -----------------------------------------------------------------------
// Global port state array
// -----------------------------------------------------------------------
PortStateT ports[MAX_PORTS];

// -----------------------------------------------------------------------
// Global instance handle
// -----------------------------------------------------------------------
static HANDLE ghInstance = NULL;

// -----------------------------------------------------------------------
// Dynamically resolved PostMessage
//
// comm.drv is loaded from [boot] before USER.EXE, so we can't have a
// static import for PostMessage. Resolve it on first use via
// GetProcAddress(GetModuleHandle("USER"), "PostMessage").
// -----------------------------------------------------------------------
PostMessageProcT pfnPostMessage = NULL;

// ISR hit counter for diagnostics
volatile uint16_t isrHitCount = 0;


// -----------------------------------------------------------------------
// applyBaudRate - Set the baud rate divisor on the UART
//
// The DCB BaudRate field is a 16-bit UINT. For rates that fit in 16 bits
// (up to 57600), the raw value is used directly. For higher rates like
// 115200, CBR_* index constants (0xFF00+) encode the rate. We detect
// these and translate via cbrToBaud().
// -----------------------------------------------------------------------
void applyBaudRate(PortStateT *port, uint16_t baud)
{
    uint32_t actualBaud;
    uint16_t divisor;
    uint8_t  lcr;
    uint16_t base;

    if (baud == 0) {
        return;
    }

    // Translate CBR_* index constants to actual baud rate
    if ((baud & 0xFF00) == 0xFF00) {
        actualBaud = cbrToBaud(baud);
    } else {
        actualBaud = (uint32_t)baud;
    }

    if (actualBaud == 0) {
        return;
    }

    base    = port->baseAddr;
    divisor = (uint16_t)(BAUD_DIVISOR_BASE / actualBaud);

    // Set DLAB to access divisor latch
    lcr = (uint8_t)_inp(base + UART_LCR);
    _outp(base + UART_LCR, lcr | LCR_DLAB);

    _outp(base + UART_DLL, (uint8_t)(divisor & 0xFF));
    _outp(base + UART_DLM, (uint8_t)(divisor >> 8));

    // Clear DLAB
    _outp(base + UART_LCR, lcr);

    port->baudRate = baud;
}


// -----------------------------------------------------------------------
// applyLineParams - Set word length, parity, and stop bits on UART
// -----------------------------------------------------------------------
void applyLineParams(PortStateT *port, uint8_t byteSize, uint8_t parity, uint8_t stopBits)
{
    uint8_t  lcr;
    uint16_t base;

    base = port->baseAddr;
    lcr  = 0;

    // Word length
    if (byteSize >= 5 && byteSize <= 8) {
        lcr |= (byteSize - 5);
    } else {
        lcr |= LCR_WLS_8;
    }

    // Stop bits
    if (stopBits == 2) {
        lcr |= LCR_STB;
    }

    // Parity
    switch (parity) {
        case ODDPARITY:
            lcr |= LCR_PEN;
            break;
        case EVENPARITY:
            lcr |= LCR_PEN | LCR_EPS;
            break;
        case MARKPARITY:
            lcr |= LCR_PEN | LCR_SPAR;
            break;
        case SPACEPARITY:
            lcr |= LCR_PEN | LCR_EPS | LCR_SPAR;
            break;
        case NOPARITY:
        default:
            break;
    }

    _outp(base + UART_LCR, lcr);

    port->byteSize = byteSize;
    port->parity   = parity;
    port->stopBits = stopBits;
}


// -----------------------------------------------------------------------
// cbrToBaud - Translate CBR_* index constant to actual baud rate
//
// Returns baud rate as uint32_t (needed for 115200 which exceeds 16 bits).
// Returns 0 for unrecognized constants.
// -----------------------------------------------------------------------
static uint32_t cbrToBaud(uint16_t cbr)
{
    switch (cbr) {
        case CBR_110:
            return 110UL;
        case CBR_300:
            return 300UL;
        case CBR_600:
            return 600UL;
        case CBR_1200:
            return 1200UL;
        case CBR_2400:
            return 2400UL;
        case CBR_4800:
            return 4800UL;
        case CBR_9600:
            return 9600UL;
        case CBR_14400:
            return 14400UL;
        case CBR_19200:
            return 19200UL;
        case CBR_38400:
            return 38400UL;
        case CBR_56000:
            return 56000UL;
        case CBR_115200:
            return 115200UL;
        default:
            return 0UL;
    }
}


// -----------------------------------------------------------------------
// cclrbrk - Clear break signal (ordinal 14)
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export cclrbrk(int16_t commId)
{
    PortStateT *port;
    uint8_t     lcr;

    dbgInt16("COMM.DRV: cclrbrk Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return -1;
    }

    lcr = (uint8_t)_inp(port->baseAddr + UART_LCR);
    _outp(port->baseAddr + UART_LCR, lcr & ~LCR_SBRK);

    port->breakState = FALSE;
    return 0;
}


// -----------------------------------------------------------------------
// cevt - Set event mask and return pointer to event word (ordinal 11)
//
// Returns a FAR pointer to the event word (packed into int32_t).
// This matches the stock COMM.DRV behavior -- the event word is a
// volatile uint16_t that accumulates event bits until cleared.
// -----------------------------------------------------------------------
int32_t FAR PASCAL _export cevt(int16_t commId, int16_t evtMask)
{
    PortStateT *port;
    uint16_t FAR *ptr;
    int32_t       retVal;

#if DBG_ENABLED
    {
        uint16_t ssSeg;
        uint16_t bpVal;
        _asm mov ssSeg, ss
        _asm mov bpVal, bp
        dbgHex16("COMM.DRV: cevt SS", ssSeg);
        dbgHex16("COMM.DRV: cevt BP", bpVal);
        dbgDump("COMM.DRV: cevt stk", (void FAR *)((uint32_t)ssSeg << 16 | (bpVal + 6)), 16);
    }
#endif

    dbgInt16("COMM.DRV: cevt Id", commId);
    dbgHex16("COMM.DRV: cevt mask", (uint16_t)evtMask);

    if (commId < 0 || commId >= MAX_PORTS) {
        return 0L;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        dbgStr("COMM.DRV: cevt not open\r\n");
        return 0L;
    }

    port->comDeb.evtMask = (uint16_t)evtMask;

    ptr = &port->comDeb.evtWord;
    retVal = (int32_t)(void FAR *)ptr;
    dbgHex16("COMM.DRV: cevt retSeg", (uint16_t)(retVal >> 16));
    dbgHex16("COMM.DRV: cevt retOff", (uint16_t)(retVal & 0xFFFF));
    dbgStr("COMM.DRV: cevt OK\r\n");
    return retVal;
}


// -----------------------------------------------------------------------
// cevtget - Read and clear event word (ordinal 12)
//
// Returns current event bits masked by evtMask, then clears those bits.
// -----------------------------------------------------------------------
uint16_t FAR PASCAL _export cevtget(int16_t commId, int16_t evtMask)
{
    PortStateT *port;
    uint16_t    events;

    dbgInt16("COMM.DRV: cevtget Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return 0;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return 0;
    }

    _disable();
    events = port->comDeb.evtWord & (uint16_t)evtMask;
    port->comDeb.evtWord &= ~(uint16_t)evtMask;
    _enable();

    return events;
}


// -----------------------------------------------------------------------
// cextfcn - Escape function for DTR/RTS/break control (ordinal 9)
//
// Note: 16-bit API returns 0 on success (unlike Win32 nonzero=success).
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export cextfcn(int16_t commId, int16_t func)
{
    PortStateT *port;
    uint8_t     mcr;
    uint16_t    base;

    dbgInt16("COMM.DRV: cextfcn Id", commId);
    dbgInt16("COMM.DRV: cextfcn func", func);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return -1;
    }

    base = port->baseAddr;
    mcr  = (uint8_t)_inp(base + UART_MCR);

    switch (func) {
        case SETDTR:
            mcr |= MCR_DTR;
            port->dtrState = TRUE;
            break;
        case CLRDTR:
            mcr &= ~MCR_DTR;
            port->dtrState = FALSE;
            break;
        case SETRTS:
            mcr |= MCR_RTS;
            port->rtsState = TRUE;
            break;
        case CLRRTS:
            mcr &= ~MCR_RTS;
            port->rtsState = FALSE;
            break;
        case ESC_SETBREAK:
            return csetbrk(commId);
        case ESC_CLRBREAK:
            return cclrbrk(commId);
        case RESETDEV:
            // No-op for serial ports
            break;
        case SETXON:
            // Resume TX as if XON received
            _disable();
            port->txStopped = FALSE;
            if (port->txCount > 0) {
                _outp(base + UART_IER, (uint8_t)(_inp(base + UART_IER) | IER_THRE));
            }
            _enable();
            return 0;
        case SETXOFF:
            // Stop TX as if XOFF received
            port->txStopped = TRUE;
            return 0;
        default:
            return -1;
    }

    _outp(base + UART_MCR, mcr);
    return 0;
}


// -----------------------------------------------------------------------
// cflush - Flush receive or transmit buffer (ordinal 10)
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export cflush(int16_t commId, int16_t queue)
{
    PortStateT *port;

    dbgInt16("COMM.DRV: cflush Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return -1;
    }

    _disable();
    if (queue == FLUSH_RX) {
        port->rxHead  = 0;
        port->rxTail  = 0;
        port->rxCount = 0;
        port->comDeb.qInHead  = 0;
        port->comDeb.qInTail  = 0;
        port->comDeb.qInCount = 0;
        // Reset FIFO to clear hardware buffer too
        if (port->is16550 && port->fifoEnabled) {
            _outp(port->baseAddr + UART_FCR, FCR_ENABLE | FCR_RX_RESET | port->fifoTrigger);
        }
    } else {
        port->txHead  = 0;
        port->txTail  = 0;
        port->txCount = 0;
        port->comDeb.qOutHead  = 0;
        port->comDeb.qOutTail  = 0;
        port->comDeb.qOutCount = 0;
        if (port->is16550 && port->fifoEnabled) {
            _outp(port->baseAddr + UART_FCR, FCR_ENABLE | FCR_TX_RESET | port->fifoTrigger);
        }
    }
    _enable();

    return 0;
}


// -----------------------------------------------------------------------
// commWriteString - Write data (ordinal 19, alias for sndcom)
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export commWriteString(int16_t commId, void FAR *buf, int16_t len)
{
    dbgInt16("COMM.DRV: commWriteStr Id", commId);
    return sndcom(commId, buf, len);
}


// -----------------------------------------------------------------------
// commNotifyWndProc - Ordinal 101 stub (undocumented, Win 3.1 compat)
//
// The stock COMM.DRV and CyberCom export an unnamed function at ordinal
// 101.  Purpose is undocumented; may be an internal callback used by
// USER.EXE.  CyberCom's implementation uses plain RETF (no params).
// Return 0 (not handled).
// -----------------------------------------------------------------------
int FAR PASCAL _export commNotifyWndProc(void)
{
    dbgStr("COMM.DRV: ord101 called\r\n");
    return 0;
}


// -----------------------------------------------------------------------
// csetbrk - Assert break signal (ordinal 13)
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export csetbrk(int16_t commId)
{
    PortStateT *port;
    uint8_t     lcr;

    dbgInt16("COMM.DRV: csetbrk Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return -1;
    }

    lcr = (uint8_t)_inp(port->baseAddr + UART_LCR);
    _outp(port->baseAddr + UART_LCR, lcr | LCR_SBRK);

    port->breakState = TRUE;
    return 0;
}


// -----------------------------------------------------------------------
// ctx - Send single character with priority (ordinal 6)
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export ctx(int16_t commId, int16_t ch)
{
    PortStateT *port;

    dbgInt16("COMM.DRV: ctx Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return -1;
    }

    _disable();
    port->txImmediate = ch;
    // Enable THRE interrupt to get it sent
    _outp(port->baseAddr + UART_IER, (uint8_t)(_inp(port->baseAddr + UART_IER) | IER_THRE));
    _enable();

    return 0;
}


// -----------------------------------------------------------------------
// detect16550 - Test if the UART at baseAddr is a 16550 with working FIFOs
//
// Returns 1 if 16550A (working FIFO), 0 otherwise.
// -----------------------------------------------------------------------
int16_t detect16550(uint16_t baseAddr)
{
    uint8_t iir;

    // Try to enable FIFOs
    _outp(baseAddr + UART_FCR, FCR_ENABLE);

    // Read IIR -- bits 7:6 should be set if FIFOs are enabled
    iir = (uint8_t)_inp(baseAddr + UART_IIR);

    // Disable FIFOs for now (we'll re-enable properly later)
    _outp(baseAddr + UART_FCR, 0);

    // 16550A has both bits 7:6 set when FIFOs enabled
    // Plain 16550 (broken FIFO) only sets bit 7
    return ((iir & IIR_FIFO_MASK) == IIR_FIFO_MASK) ? 1 : 0;
}


// -----------------------------------------------------------------------
// enableFifo - Enable 16550 FIFOs with configurable trigger level
//
// Uses port->fifoTrigger (set from SYSTEM.INI COMnRxTRIGGER, default 8).
// Respects port->fifoEnabled (set from SYSTEM.INI COMnFIFO, default 1).
// -----------------------------------------------------------------------
void enableFifo(PortStateT *port)
{
    if (!port->is16550 || !port->fifoEnabled) {
        return;
    }

    // Enable + reset both FIFOs + configured RX trigger level
    _outp(port->baseAddr + UART_FCR, FCR_ENABLE | FCR_RX_RESET | FCR_TX_RESET | port->fifoTrigger);
}


// -----------------------------------------------------------------------
// enableNotification - Register window for WM_COMMNOTIFY (ordinal 100)
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export enableNotification(int16_t commId, HWND hwnd, int16_t rxThresh, int16_t txThresh)
{
    PortStateT *port;

    dbgInt16("COMM.DRV: enableNotif Id", commId);
    dbgHex16("COMM.DRV: enableNotif hwnd", (uint16_t)hwnd);
    dbgInt16("COMM.DRV: enableNotif rxTh", rxThresh);
    dbgInt16("COMM.DRV: enableNotif txTh", txThresh);

    if (commId < 0 || commId >= MAX_PORTS) {
        return FALSE;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        dbgStr("COMM.DRV: enableNotif not open\r\n");
        return FALSE;
    }

    // Lazily resolve PostMessage from USER.EXE
    // (not available at boot when comm.drv is loaded from [boot])
    if (!pfnPostMessage) {
        HMODULE hUser = GetModuleHandle("USER");
        if (hUser) {
            pfnPostMessage = (PostMessageProcT)GetProcAddress(hUser, "PostMessage");
        }
    }

    port->hwndNotify     = hwnd;
    port->rxNotifyThresh = rxThresh;
    port->txNotifyThresh = txThresh;

    dbgStr("COMM.DRV: enableNotif OK\r\n");
    return TRUE;
}


// -----------------------------------------------------------------------
// freeBuffers - Free ring buffers for a port
// -----------------------------------------------------------------------
static int16_t freeBuffers(PortStateT *port)
{
    HGLOBAL hMem;

    if (port->rxBuf) {
        hMem = (HGLOBAL)LOWORD(GlobalHandle(SELECTOROF(port->rxBuf)));
        if (hMem) {
            GlobalUnlock(hMem);
            GlobalFree(hMem);
        }
        port->rxBuf = NULL;
    }

    if (port->txBuf) {
        hMem = (HGLOBAL)LOWORD(GlobalHandle(SELECTOROF(port->txBuf)));
        if (hMem) {
            GlobalUnlock(hMem);
            GlobalFree(hMem);
        }
        port->txBuf = NULL;
    }

    return 0;
}


// -----------------------------------------------------------------------
// getdcb - Return pointer to internal DCB (ordinal 15)
//
// Takes int16_t commId (2 bytes, RETF 2).  Returns DCB FAR * in DX:AX.
// The caller (USER.EXE / COMMTASK.DLL) copies from this pointer.
// CyberCom confirms: RETF 2, return pointer.
// -----------------------------------------------------------------------
DCB FAR * FAR PASCAL _export getdcb(int16_t commId)
{
    PortStateT *port;

    dbgInt16("COMM.DRV: getdcb Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        dbgStr("COMM.DRV: getdcb bad id\r\n");
        return NULL;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        dbgStr("COMM.DRV: getdcb not open\r\n");
        return NULL;
    }

    dbgHex16("COMM.DRV: getdcb isrHits", isrHitCount);
    dbgStr("COMM.DRV: getdcb OK\r\n");
    return &port->dcb;
}


// -----------------------------------------------------------------------
// inicom - Open a COM port (ordinal 1)
//
// Opens the port specified in dcb->Id, allocates ring buffers, hooks ISR,
// enables interrupts, and applies DCB settings.
//
// rxBuf and rxSize are ignored (legacy params); we allocate our own buffers.
//
// Returns commId (0-3) on success, negative error code on failure.
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export inicom(DCB FAR *dcb)
{
    int16_t     commId;
    PortStateT *port;
    uint16_t    rxBufSize;
    uint16_t    txBufSize;
    uint8_t     mcr;

    dbgStr("COMM.DRV: inicom enter\r\n");

    // Dump raw stack to see actual parameters passed by caller
    {
        uint16_t bpVal;
        uint16_t ssVal;
        void FAR *stkPtr;
        _asm mov bpVal, bp
        _asm mov ssVal, ss
        stkPtr = (void FAR *)((uint32_t)ssVal << 16 | (bpVal + 6));
        dbgHex16("COMM.DRV: inicom SS", ssVal);
        dbgHex16("COMM.DRV: inicom BP", bpVal);
        dbgDump("COMM.DRV: inicom stk", stkPtr, 24);
    }

    if (!dcb) {
        dbgStr("COMM.DRV: inicom NULL dcb\r\n");
        return IE_DEFAULT;
    }

    dbgFarPtr("COMM.DRV: inicom dcb", (void FAR *)dcb);
    dbgDump("COMM.DRV: inicom raw", (void FAR *)dcb, 16);
    dbgHex16("COMM.DRV: sizeof(DCB)", (uint16_t)sizeof(DCB));

    commId = dcb->Id;
    dbgInt16("COMM.DRV: inicom Id", commId);
    dbgHex16("COMM.DRV: inicom BaudRate", dcb->BaudRate);
    dbgHex16("COMM.DRV: inicom ByteSize", (uint16_t)dcb->ByteSize);
    dbgHex16("COMM.DRV: inicom Parity", (uint16_t)dcb->Parity);
    dbgHex16("COMM.DRV: inicom StopBits", (uint16_t)dcb->StopBits);

    if (commId < 0 || commId >= MAX_PORTS) {
        dbgStr("COMM.DRV: inicom IE_BADID\r\n");
        return IE_BADID;
    }

    port = &ports[commId];
    if (port->isOpen) {
        dbgStr("COMM.DRV: inicom IE_OPEN\r\n");
        return IE_OPEN;
    }

    // Initialize port state
    initPortState(port, commId);
    dbgHex16("COMM.DRV: inicom baseAddr", port->baseAddr);
    dbgHex16("COMM.DRV: inicom irq", (uint16_t)port->irq);

    // Read buffer sizes from SYSTEM.INI if available (COMnBuffer key)
    {
        char bufKey[12];
        bufKey[0] = 'C';
        bufKey[1] = 'O';
        bufKey[2] = 'M';
        bufKey[3] = (char)('1' + commId);
        bufKey[4] = 'B';
        bufKey[5] = 'u';
        bufKey[6] = 'f';
        bufKey[7] = 'f';
        bufKey[8] = 'e';
        bufKey[9] = 'r';
        bufKey[10] = '\0';
        rxBufSize = readSystemIni("386Enh", bufKey, DEFAULT_RX_SIZE);
    }
    txBufSize = rxBufSize;
    dbgHex16("COMM.DRV: inicom rxBufSize", rxBufSize);

    // Allocate ring buffers
    if (initBuffers(port, rxBufSize, txBufSize) != 0) {
        dbgStr("COMM.DRV: inicom IE_MEMORY\r\n");
        return IE_MEMORY;
    }
    dbgStr("COMM.DRV: inicom buffers OK\r\n");

    // Detect 16550 FIFO
    port->is16550 = (uint8_t)detect16550(port->baseAddr);
    dbgHex16("COMM.DRV: inicom is16550", (uint16_t)port->is16550);

    // Hook ISR
    if (hookIsr(port) != 0) {
        dbgStr("COMM.DRV: inicom hookIsr FAIL\r\n");
        freeBuffers(port);
        return IE_HARDWARE;
    }
    dbgStr("COMM.DRV: inicom ISR hooked\r\n");

    port->isOpen = TRUE;

    // Enable FIFOs if 16550 detected
    enableFifo(port);

    // Apply DCB settings
    _fmemcpy(&port->dcb, dcb, sizeof(DCB));
    applyBaudRate(port, dcb->BaudRate);
    applyLineParams(port, dcb->ByteSize, dcb->Parity, dcb->StopBits);

    // Set flow control from DCB
    if (dcb->fOutxCtsFlow && dcb->fInX) {
        port->hsMode = HS_BOTH;
    } else if (dcb->fOutxCtsFlow) {
        port->hsMode = HS_RTSCTS;
    } else if (dcb->fInX) {
        port->hsMode = HS_XONXOFF;
    } else {
        port->hsMode = HS_NONE;
    }

    port->xonChar  = dcb->XonChar;
    port->xoffChar = dcb->XoffChar;
    port->xonLim   = dcb->XonLim;
    port->xoffLim  = dcb->XoffLim;

    // Raise DTR and RTS, enable OUT2 (master interrupt gate)
    mcr = MCR_DTR | MCR_RTS | MCR_OUT2;
    _outp(port->baseAddr + UART_MCR, mcr);
    port->dtrState = TRUE;
    port->rtsState = TRUE;

    // Clear any pending status
    _inp(port->baseAddr + UART_LSR);
    port->comDeb.msrShadow = (uint8_t)_inp(port->baseAddr + UART_MSR);
    _inp(port->baseAddr + UART_RBR);

    // Populate ComDEB for third-party compatibility
    port->comDeb.port      = port->baseAddr;
    port->comDeb.baudRate   = port->baudRate;
    port->comDeb.qInSize    = port->rxSize;
    port->comDeb.qOutSize   = port->txSize;

    // Enable receive and line status interrupts
    _outp(port->baseAddr + UART_IER, IER_RDA | IER_LSI | IER_MSI);

    dbgInt16("COMM.DRV: inicom OK, ret", commId);
    return commId;
}


// -----------------------------------------------------------------------
// initBuffers - Allocate ring buffers via GlobalAlloc
// -----------------------------------------------------------------------
static int16_t initBuffers(PortStateT *port, uint16_t rxSz, uint16_t txSz)
{
    HGLOBAL hRx;
    HGLOBAL hTx;

    hRx = GlobalAlloc(GMEM_MOVEABLE | GMEM_ZEROINIT, (DWORD)rxSz);
    if (!hRx) {
        return -1;
    }

    hTx = GlobalAlloc(GMEM_MOVEABLE | GMEM_ZEROINIT, (DWORD)txSz);
    if (!hTx) {
        GlobalFree(hRx);
        return -1;
    }

    port->rxBuf  = (uint8_t FAR *)GlobalLock(hRx);
    port->rxSize = rxSz;
    port->rxHead = 0;
    port->rxTail = 0;
    port->rxCount = 0;

    port->txBuf  = (uint8_t FAR *)GlobalLock(hTx);
    port->txSize = txSz;
    port->txHead = 0;
    port->txTail = 0;
    port->txCount = 0;

    return 0;
}


// -----------------------------------------------------------------------
// initPortState - Initialize a port state structure with defaults
//
// Reads COMnBase, COMnIRQ, COMnFIFO, and COMnRxTRIGGER from
// SYSTEM.INI [386Enh] to support non-standard port configurations.
// -----------------------------------------------------------------------
static void initPortState(PortStateT *port, int16_t commId)
{
    uint16_t baseAddr;
    uint8_t  irq;
    uint16_t fifoEnabled;
    uint16_t rxTrigger;

    _fmemset(port, 0, sizeof(PortStateT));

    port->commId = commId;

    // Read port address and IRQ from SYSTEM.INI (or use defaults)
    readPortConfig(commId, &baseAddr, &irq);
    port->baseAddr = baseAddr;
    port->irq      = irq;

    // Read FIFO enable setting (default: enabled)
    {
        char fifoKey[10];
        fifoKey[0] = 'C';
        fifoKey[1] = 'O';
        fifoKey[2] = 'M';
        fifoKey[3] = (char)('1' + commId);
        fifoKey[4] = 'F';
        fifoKey[5] = 'I';
        fifoKey[6] = 'F';
        fifoKey[7] = 'O';
        fifoKey[8] = '\0';
        fifoEnabled = readSystemIni("386Enh", fifoKey, 1);
    }
    port->fifoEnabled = (uint8_t)(fifoEnabled ? 1 : 0);

    // Read RX trigger level from SYSTEM.INI (default: 8)
    {
        char trigKey[16];
        trigKey[0]  = 'C';
        trigKey[1]  = 'O';
        trigKey[2]  = 'M';
        trigKey[3]  = (char)('1' + commId);
        trigKey[4]  = 'R';
        trigKey[5]  = 'x';
        trigKey[6]  = 'T';
        trigKey[7]  = 'R';
        trigKey[8]  = 'I';
        trigKey[9]  = 'G';
        trigKey[10] = 'G';
        trigKey[11] = 'E';
        trigKey[12] = 'R';
        trigKey[13] = '\0';
        rxTrigger = readSystemIni("386Enh", trigKey, 8);
    }
    switch (rxTrigger) {
        case 1:
            port->fifoTrigger = FCR_TRIG_1;
            break;
        case 4:
            port->fifoTrigger = FCR_TRIG_4;
            break;
        case 14:
            port->fifoTrigger = FCR_TRIG_14;
            break;
        case 8:
        default:
            port->fifoTrigger = FCR_TRIG_8;
            break;
    }

    port->xonChar  = 0x11;   // DC1
    port->xoffChar = 0x13;   // DC3
    port->xonLim   = DEFAULT_RX_SIZE / 4;
    port->xoffLim  = DEFAULT_RX_SIZE / 4;

    port->txImmediate    = -1;
    port->rxNotifyThresh = -1;
    port->txNotifyThresh = -1;
}


// -----------------------------------------------------------------------
// primeTx - Prime the transmitter by enabling THRE interrupt
//
// Called after writing data to the TX ring buffer to kick off
// transmission if it's not already running.
// -----------------------------------------------------------------------
void primeTx(PortStateT *port)
{
    uint8_t ier;

    ier = (uint8_t)_inp(port->baseAddr + UART_IER);
    if (!(ier & IER_THRE)) {
        _outp(port->baseAddr + UART_IER, ier | IER_THRE);
    }
}


// -----------------------------------------------------------------------
// reactivateOpenCommPorts - Reactivate all ports after task switch (ordinal 18)
//
// Called by Windows when switching back to this VM.
// Re-enables interrupts and restores MCR state.
// -----------------------------------------------------------------------
void FAR PASCAL _export reactivateOpenCommPorts(void)
{
    int16_t     i;
    PortStateT *port;
    uint8_t     mcr;

    dbgStr("COMM.DRV: reactivate\r\n");

    for (i = 0; i < MAX_PORTS; i++) {
        port = &ports[i];
        if (!port->isOpen) {
            continue;
        }

        // Restore MCR (DTR, RTS, OUT2)
        mcr = MCR_OUT2;
        if (port->dtrState) {
            mcr |= MCR_DTR;
        }
        if (port->rtsState) {
            mcr |= MCR_RTS;
        }
        _outp(port->baseAddr + UART_MCR, mcr);

        // Re-enable FIFOs
        enableFifo(port);

        // Re-enable interrupts
        _outp(port->baseAddr + UART_IER, IER_RDA | IER_LSI | IER_MSI);
        if (port->txCount > 0) {
            _outp(port->baseAddr + UART_IER, (uint8_t)(_inp(port->baseAddr + UART_IER) | IER_THRE));
        }

        // Unmask IRQ at PIC
        {
            uint8_t picMask = (uint8_t)_inp(PIC_DATA);
            picMask &= ~port->irqMask;
            _outp(PIC_DATA, picMask);
        }
    }
}


// -----------------------------------------------------------------------
// readCommString - Read data (ordinal 20, alias for reccom)
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export readCommString(int16_t commId, void FAR *buf, int16_t len)
{
    dbgInt16("COMM.DRV: readCommStr Id", commId);
    return reccom(commId, buf, len);
}


// -----------------------------------------------------------------------
// readPortConfig - Read port base address and IRQ from SYSTEM.INI
//
// Checks [386Enh] for COMnBase (hex) and COMnIRQ overrides.
// Falls back to standard defaults if not present.
// -----------------------------------------------------------------------
static void readPortConfig(int16_t commId, uint16_t FAR *baseAddr, uint8_t FAR *irq)
{
    char key[10];
    char buf[16];

    // Defaults
    *baseAddr = portBase[commId];
    *irq      = portIrq[commId];

    // Check COMnBase (e.g., COM3Base=3E8)
    key[0] = 'C';
    key[1] = 'O';
    key[2] = 'M';
    key[3] = (char)('1' + commId);
    key[4] = 'B';
    key[5] = 'a';
    key[6] = 's';
    key[7] = 'e';
    key[8] = '\0';

    GetPrivateProfileString("386Enh", key, "", buf, sizeof(buf), "SYSTEM.INI");
    if (buf[0] != '\0') {
        // Parse hex string manually (no strtoul in small model CRT)
        uint16_t val = 0;
        int16_t  i   = 0;
        char     ch;

        while (buf[i] != '\0') {
            ch = buf[i];
            val <<= 4;
            if (ch >= '0' && ch <= '9') {
                val |= (uint16_t)(ch - '0');
            } else if (ch >= 'A' && ch <= 'F') {
                val |= (uint16_t)(ch - 'A' + 10);
            } else if (ch >= 'a' && ch <= 'f') {
                val |= (uint16_t)(ch - 'a' + 10);
            }
            i++;
        }
        if (val != 0) {
            *baseAddr = val;
        }
    }

    // Check COMnIRQ (e.g., COM3Irq=5)
    key[4] = 'I';
    key[5] = 'r';
    key[6] = 'q';
    key[7] = '\0';

    {
        uint16_t irqVal = readSystemIni("386Enh", key, (uint16_t)*irq);
        if (irqVal > 0 && irqVal <= 7) {
            *irq = (uint8_t)irqVal;
        }
    }
}


// -----------------------------------------------------------------------
// readSystemIni - Read an unsigned integer value from SYSTEM.INI
// -----------------------------------------------------------------------
static uint16_t readSystemIni(const char FAR *section, const char FAR *key, uint16_t defVal)
{
    return (uint16_t)GetPrivateProfileInt(section, key, (int)defVal, "SYSTEM.INI");
}


// -----------------------------------------------------------------------
// reccom - Read from RX ring buffer (ordinal 4)
//
// Copies up to len bytes from the receive ring buffer into buf.
// Returns number of bytes read, or negative error code.
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export reccom(int16_t commId, void FAR *buf, int16_t len)
{
    PortStateT  *port;
    uint8_t FAR *dst;
    int16_t      bytesRead;

    dbgInt16("COMM.DRV: reccom Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return -1;
    }

    dst       = (uint8_t FAR *)buf;
    bytesRead = 0;

    _disable();
    while (bytesRead < len && port->rxCount > 0) {
        *dst++ = port->rxBuf[port->rxTail];
        port->rxTail++;
        if (port->rxTail >= port->rxSize) {
            port->rxTail = 0;
        }
        port->rxCount--;
        bytesRead++;
    }
    _enable();

    // If flow control was asserted and buffer has drained, deassert
    if (port->rxStopped && port->rxCount <= port->xonLim) {
        _disable();
        port->rxStopped = FALSE;

        if (port->hsMode == HS_XONXOFF || port->hsMode == HS_BOTH) {
            port->txImmediate = port->xonChar;
            _outp(port->baseAddr + UART_IER, (uint8_t)(_inp(port->baseAddr + UART_IER) | IER_THRE));
        }
        if (port->hsMode == HS_RTSCTS || port->hsMode == HS_BOTH) {
            _outp(port->baseAddr + UART_MCR, (uint8_t)(_inp(port->baseAddr + UART_MCR) | MCR_RTS));
        }
        _enable();
    }

    // Sync ComDEB queue counts
    port->comDeb.qInCount = port->rxCount;
    port->comDeb.qInTail  = port->rxTail;

    return bytesRead;
}


// -----------------------------------------------------------------------
// setcom - Apply DCB settings to hardware (ordinal 2)
//
// Takes DCB FAR * (4 bytes, RETF 4).  CommId is in dcb->Id.
// Both USER.EXE and COMMTASK.DLL push 4 bytes for this call.
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export setcom(DCB FAR *dcb)
{
    int16_t     commId;
    PortStateT *port;

    dbgStr("COMM.DRV: setcom enter\r\n");

    if (!dcb) {
        dbgStr("COMM.DRV: setcom NULL dcb\r\n");
        return -1;
    }

    commId = dcb->Id;
    dbgInt16("COMM.DRV: setcom Id", commId);
    dbgHex16("COMM.DRV: setcom BaudRate", dcb->BaudRate);
    dbgHex16("COMM.DRV: setcom ByteSize", (uint16_t)dcb->ByteSize);
    dbgHex16("COMM.DRV: setcom Parity", (uint16_t)dcb->Parity);
    dbgHex16("COMM.DRV: setcom StopBits", (uint16_t)dcb->StopBits);

    if (commId < 0 || commId >= MAX_PORTS) {
        dbgStr("COMM.DRV: setcom IE_BADID\r\n");
        return IE_BADID;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        dbgStr("COMM.DRV: setcom port not open\r\n");
        return -1;
    }

    // Save DCB
    _fmemcpy(&port->dcb, dcb, sizeof(DCB));

    // Apply hardware settings
    _disable();

    applyBaudRate(port, dcb->BaudRate);
    applyLineParams(port, dcb->ByteSize, dcb->Parity, dcb->StopBits);

    // Update flow control
    if (dcb->fOutxCtsFlow && dcb->fInX) {
        port->hsMode = HS_BOTH;
    } else if (dcb->fOutxCtsFlow) {
        port->hsMode = HS_RTSCTS;
    } else if (dcb->fInX) {
        port->hsMode = HS_XONXOFF;
    } else {
        port->hsMode = HS_NONE;
    }

    port->xonChar  = dcb->XonChar;
    port->xoffChar = dcb->XoffChar;
    port->xonLim   = dcb->XonLim;
    port->xoffLim  = dcb->XoffLim;

    // Sync ComDEB shadow fields
    port->comDeb.baudRate  = port->baudRate;
    port->comDeb.lcrShadow = (uint8_t)_inp(port->baseAddr + UART_LCR);
    port->comDeb.mcrShadow = (uint8_t)_inp(port->baseAddr + UART_MCR);

    _enable();

    dbgStr("COMM.DRV: setcom OK\r\n");
    return 0;
}


// -----------------------------------------------------------------------
// setque - Resize RX/TX buffers (ordinal 3)
//
// Caller passes port ID and requested RX/TX buffer sizes.
// We manage our own GlobalAlloc'd buffers.
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export setque(int16_t commId, int16_t rxSz, int16_t txSz)
{
    PortStateT *port;

    dbgInt16("COMM.DRV: setque Id", commId);
    dbgInt16("COMM.DRV: setque rxSz", rxSz);
    dbgInt16("COMM.DRV: setque txSz", txSz);

    if (commId < 0 || commId >= MAX_PORTS) {
        dbgStr("COMM.DRV: setque bad id\r\n");
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        dbgStr("COMM.DRV: setque port not open\r\n");
        return -1;
    }

    _disable();
    freeBuffers(port);
    if (initBuffers(port, (uint16_t)rxSz, (uint16_t)txSz) != 0) {
        _enable();
        dbgStr("COMM.DRV: setque IE_MEMORY\r\n");
        return IE_MEMORY;
    }
    // Sync ComDEB queue sizes
    port->comDeb.qInSize   = port->rxSize;
    port->comDeb.qInCount  = 0;
    port->comDeb.qInHead   = 0;
    port->comDeb.qInTail   = 0;
    port->comDeb.qOutSize  = port->txSize;
    port->comDeb.qOutCount = 0;
    port->comDeb.qOutHead  = 0;
    port->comDeb.qOutTail  = 0;
    _enable();

    dbgStr("COMM.DRV: setque OK\r\n");
    return 0;
}


// -----------------------------------------------------------------------
// sndcom - Write to TX ring buffer and prime transmitter (ordinal 5)
//
// Copies up to len bytes from buf into the transmit ring buffer.
// Returns number of bytes written, or negative error code.
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export sndcom(int16_t commId, void FAR *buf, int16_t len)
{
    PortStateT       *port;
    uint8_t FAR      *src;
    int16_t           bytesWritten;

    dbgInt16("COMM.DRV: sndcom Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        return -1;
    }

    src          = (uint8_t FAR *)buf;
    bytesWritten = 0;

    _disable();
    while (bytesWritten < len) {
        if (port->txCount >= port->txSize) {
            port->errorFlags |= CE_TXFULL;
            break;
        }

        port->txBuf[port->txHead] = *src++;
        port->txHead++;
        if (port->txHead >= port->txSize) {
            port->txHead = 0;
        }
        port->txCount++;
        bytesWritten++;
    }
    _enable();

    // Sync ComDEB queue counts
    port->comDeb.qOutCount = port->txCount;
    port->comDeb.qOutHead  = port->txHead;

    // Prime transmitter if we wrote anything
    if (bytesWritten > 0 && !port->txStopped) {
        primeTx(port);
    }

    return bytesWritten;
}


// -----------------------------------------------------------------------
// stacom - Return and clear error flags plus COMSTAT (ordinal 8)
//
// Returns accumulated error flags (CE_*) and fills the COMSTAT
// structure with current buffer counts and status.
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export stacom(int16_t commId, COMSTAT FAR *stat)
{
    PortStateT *port;
    int16_t     errors;

    dbgInt16("COMM.DRV: stacom Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        dbgStr("COMM.DRV: stacom bad id\r\n");
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        dbgStr("COMM.DRV: stacom not open\r\n");
        return -1;
    }

    _disable();
    errors = (int16_t)port->errorFlags;
    port->errorFlags = 0;
    _enable();

    if (stat) {
        stat->status = 0;
        if (port->txStopped) {
            stat->status |= CSTF_XOFFHOLD;
        }
        stat->cbInQue  = port->rxCount;
        stat->cbOutQue = port->txCount;
    }

    dbgHex16("COMM.DRV: stacom errors", (uint16_t)errors);
    return errors;
}


// -----------------------------------------------------------------------
// suspendOpenCommPorts - Suspend all ports during task switch (ordinal 17)
//
// Called by Windows when switching away from this VM.
// Disables interrupts on all open ports to prevent ISR problems.
// -----------------------------------------------------------------------
void FAR PASCAL _export suspendOpenCommPorts(void)
{
    int16_t     i;
    PortStateT *port;

    dbgStr("COMM.DRV: suspend\r\n");

    for (i = 0; i < MAX_PORTS; i++) {
        port = &ports[i];
        if (!port->isOpen) {
            continue;
        }

        // Disable UART interrupts
        _outp(port->baseAddr + UART_IER, 0);

        // Mask IRQ at PIC
        {
            uint8_t picMask = (uint8_t)_inp(PIC_DATA);
            picMask |= port->irqMask;
            _outp(PIC_DATA, picMask);
        }
    }
}


// -----------------------------------------------------------------------
// trmcom - Close a COM port (ordinal 7)
//
// Disables interrupts, drops DTR/RTS, unhooks ISR, frees buffers.
// Returns 0 on success.
// -----------------------------------------------------------------------
int16_t FAR PASCAL _export trmcom(int16_t commId)
{
    PortStateT *port;

    dbgInt16("COMM.DRV: trmcom Id", commId);

    if (commId < 0 || commId >= MAX_PORTS) {
        return -1;
    }

    port = &ports[commId];
    if (!port->isOpen) {
        dbgStr("COMM.DRV: trmcom port not open\r\n");
        return -1;
    }

    // Disable UART interrupts
    _outp(port->baseAddr + UART_IER, 0);

    // Disable FIFOs
    if (port->is16550) {
        _outp(port->baseAddr + UART_FCR, 0);
    }

    // Drop DTR, RTS, OUT2
    _outp(port->baseAddr + UART_MCR, 0);

    // Unhook ISR
    unhookIsr(port);

    // Free buffers
    freeBuffers(port);

    // Clear notification
    port->hwndNotify = NULL;

    port->isOpen = FALSE;

    dbgHex16("COMM.DRV: trmcom isrHits", isrHitCount);
    dbgStr("COMM.DRV: trmcom OK\r\n");
    return 0;
}


// -----------------------------------------------------------------------
// LibMain - DLL entry point
// -----------------------------------------------------------------------
int FAR PASCAL LibMain(HANDLE hInstance, WORD wDataSeg, WORD wHeapSize, LPSTR lpCmdLine)
{
    int16_t i;

    (void)wDataSeg;
    (void)lpCmdLine;

    ghInstance = hInstance;

    dbgStr("COMM.DRV: LibMain\r\n");

    if (wHeapSize > 0) {
        UnlockData(0);
    }

    // Zero all port states
    for (i = 0; i < MAX_PORTS; i++) {
        _fmemset(&ports[i], 0, sizeof(PortStateT));
        ports[i].txImmediate = -1;
    }

    return 1;
}


// -----------------------------------------------------------------------
// WEP - DLL exit procedure
// -----------------------------------------------------------------------
int FAR PASCAL _export WEP(int nParam)
{
    int16_t i;

    (void)nParam;

    // Close any ports still open
    for (i = 0; i < MAX_PORTS; i++) {
        if (ports[i].isOpen) {
            trmcom(i);
        }
    }

    return 1;
}