WinComm/vbx/serial.c

// serial.c - Serial port abstraction layer
//
// Wraps Windows 3.1 comm API for use by the MSComm VBX control.
// All functions operate on a comm ID returned by serialOpen().

#include <windows.h>
#include <string.h>
#include "serial.h"

// -----------------------------------------------------------------------
// Prototypes
// -----------------------------------------------------------------------
int16_t serialClose(int16_t commId);
int16_t serialConfigure(int16_t commId, int16_t port, const char FAR *settings);
BOOL    serialEnableNotify(int16_t commId, HWND hwnd, int16_t rxThreshold, int16_t txThreshold);
int16_t serialEscape(int16_t commId, int16_t func);
int16_t serialFlush(int16_t commId, int16_t queue);
UINT    serialGetEventMask(int16_t commId, UINT mask);
int16_t serialGetStatus(int16_t commId, COMSTAT FAR *stat);
int16_t serialOpen(int16_t port, int16_t inBufSize, int16_t outBufSize);
int16_t serialRead(int16_t commId, char FAR *buf, int16_t len);
int16_t serialSetHandshaking(int16_t commId, int16_t mode);
int16_t serialSetOptions(int16_t commId, BOOL nullDiscard, const char FAR *parityReplace);
int16_t serialWrite(int16_t commId, const char FAR *buf, int16_t len);


// -----------------------------------------------------------------------
// serialClose - Close an open comm port
// -----------------------------------------------------------------------
int16_t serialClose(int16_t commId)
{
    // Drop DTR and RTS before closing
    EscapeCommFunction(commId, CLRDTR);
    EscapeCommFunction(commId, CLRRTS);

    return (int16_t)CloseComm(commId);
}


// -----------------------------------------------------------------------
// serialConfigure - Set baud, parity, data bits, stop bits
// -----------------------------------------------------------------------
int16_t serialConfigure(int16_t commId, int16_t port, const char FAR *settings)
{
    DCB  dcb;
    char buf[64];
    int  rc;

    // Get current state to preserve existing settings
    rc = GetCommState(commId, &dcb);
    if (rc != 0) {
        return -1;
    }

    // Build DCB from "COMn:baud,parity,data,stop" string
    wsprintf(buf, "COM%d:%s", (int)port, (LPSTR)settings);
    rc = BuildCommDCB(buf, &dcb);
    if (rc != 0) {
        return -1;
    }

    // Ensure binary mode for reliable operation
    dcb.fBinary = 1;

    // Ensure comm ID matches our open port
    dcb.Id = (BYTE)commId;

    rc = SetCommState(&dcb);
    if (rc != 0) {
        return -1;
    }

    return 0;
}


// -----------------------------------------------------------------------
// serialEnableNotify - Enable WM_COMMNOTIFY messages
// -----------------------------------------------------------------------
BOOL serialEnableNotify(int16_t commId, HWND hwnd, int16_t rxThreshold, int16_t txThreshold)
{
    // Enable event mask for modem status line changes, errors, and breaks
    SetCommEventMask(commId, EV_CTS | EV_DSR | EV_RLSD | EV_RING | EV_ERR | EV_BREAK | EV_RXCHAR);

    return EnableCommNotification(commId, hwnd, rxThreshold, txThreshold);
}


// -----------------------------------------------------------------------
// serialEscape - Execute escape function (DTR, RTS, break control)
// -----------------------------------------------------------------------
int16_t serialEscape(int16_t commId, int16_t func)
{
    LONG rc;

    rc = EscapeCommFunction(commId, func);
    return (rc == 0) ? 0 : -1;
}


// -----------------------------------------------------------------------
// serialFlush - Flush receive or transmit buffer
// -----------------------------------------------------------------------
int16_t serialFlush(int16_t commId, int16_t queue)
{
    return (int16_t)FlushComm(commId, queue);
}


// -----------------------------------------------------------------------
// serialGetEventMask - Get and clear event mask bits
// -----------------------------------------------------------------------
UINT serialGetEventMask(int16_t commId, UINT mask)
{
    return GetCommEventMask(commId, mask);
}


// -----------------------------------------------------------------------
// serialGetStatus - Get error status and buffer counts
// -----------------------------------------------------------------------
int16_t serialGetStatus(int16_t commId, COMSTAT FAR *stat)
{
    return (int16_t)GetCommError(commId, stat);
}


// -----------------------------------------------------------------------
// serialOpen - Open a COM port with specified buffer sizes
// -----------------------------------------------------------------------
int16_t serialOpen(int16_t port, int16_t inBufSize, int16_t outBufSize)
{
    char name[8];
    int  commId;

    wsprintf(name, "COM%d", (int)port);
    commId = OpenComm(name, (UINT)inBufSize, (UINT)outBufSize);

    return (int16_t)commId;
}


// -----------------------------------------------------------------------
// serialRead - Read data from receive buffer
// -----------------------------------------------------------------------
int16_t serialRead(int16_t commId, char FAR *buf, int16_t len)
{
    return (int16_t)ReadComm(commId, (LPSTR)buf, len);
}


// -----------------------------------------------------------------------
// serialSetHandshaking - Apply handshaking mode
// -----------------------------------------------------------------------
int16_t serialSetHandshaking(int16_t commId, int16_t mode)
{
    DCB dcb;
    int rc;

    rc = GetCommState(commId, &dcb);
    if (rc != 0) {
        return -1;
    }

    // Clear all flow control settings
    dcb.fOutxCtsFlow = 0;
    dcb.fOutxDsrFlow = 0;
    dcb.fOutX        = 0;
    dcb.fInX         = 0;
    dcb.fRtsDisable  = 0;
    dcb.fRtsflow     = 0;

    switch (mode) {
    case HANDSHAKE_XONXOFF:
        dcb.fOutX    = 1;
        dcb.fInX     = 1;
        dcb.XonChar  = 0x11;  // Ctrl-Q
        dcb.XoffChar = 0x13;  // Ctrl-S
        dcb.XonLim   = 256;
        dcb.XoffLim  = 256;
        break;

    case HANDSHAKE_RTSCTS:
        dcb.fOutxCtsFlow = 1;
        dcb.fRtsflow     = 1;
        break;

    case HANDSHAKE_BOTH:
        dcb.fOutxCtsFlow = 1;
        dcb.fRtsflow     = 1;
        dcb.fOutX        = 1;
        dcb.fInX         = 1;
        dcb.XonChar      = 0x11;
        dcb.XoffChar     = 0x13;
        dcb.XonLim       = 256;
        dcb.XoffLim      = 256;
        break;

    case HANDSHAKE_NONE:
    default:
        break;
    }

    dcb.Id = (BYTE)commId;
    rc = SetCommState(&dcb);
    if (rc != 0) {
        return -1;
    }

    return 0;
}


// -----------------------------------------------------------------------
// serialSetOptions - Apply null-discard and parity-replace settings
// -----------------------------------------------------------------------
int16_t serialSetOptions(int16_t commId, BOOL nullDiscard, const char FAR *parityReplace)
{
    DCB dcb;
    int rc;

    rc = GetCommState(commId, &dcb);
    if (rc != 0) {
        return -1;
    }

    dcb.fNull = nullDiscard ? 1 : 0;

    if (parityReplace != NULL && parityReplace[0] != '\0') {
        dcb.fParity = 1;
        dcb.PeChar  = parityReplace[0];
    } else {
        dcb.fParity = 0;
        dcb.PeChar  = '\0';
    }

    dcb.Id = (BYTE)commId;
    rc = SetCommState(&dcb);
    if (rc != 0) {
        return -1;
    }

    return 0;
}


// -----------------------------------------------------------------------
// serialWrite - Write data to transmit buffer
// -----------------------------------------------------------------------
int16_t serialWrite(int16_t commId, const char FAR *buf, int16_t len)
{
    return (int16_t)WriteComm(commId, (LPSTR)buf, len);
}