/*========================================================================*/
/*  The following example routine has been provided by the Technical      */
/*  Support staff at Borland International.  It is provided as a          */
/*  courtesy and not as part of a Borland product, and as such, is        */
/*  provided without the assurance of technical support or any specific   */
/*  guarantees.                                                           */
/*========================================================================*/
/*                                                                        */
/*------------------------------------------------------------------------*/

  /*------------------------------------------------------------------*
                                 SERIAL.C

      The following code shows how to take advantage of some of
      the Turbo C extensions to the C language to do asynchronous
      communications without having to write supporting assembly-
      language routines.

      This program bypasses the less-than-adequate PC BIOS
      communications routines and installs a serial interrupt
      handler. Direct access to PC hardware allows the program to
      run at faster baud rates and eliminates the need for
      the main program to continuously poll the serial port for
      data; thus implementing background communications. Data that
      enters the serial port is stored in a circular buffer.

      * Compile this program with Test Stack Overflow OFF.

  *------------------------------------------------------------------*/

#include <dos.h>
#include <conio.h>
#include <stdio.h>
#include <string.h>
#include "serial.h"

#define VERSION 0x0101

#define FALSE           0
#define TRUE           (!FALSE)

#define NOERROR         0       /* No error               */
#define BUFOVFL         1       /* Buffer overflowed      */

#define ESC             0x1B    /* ASCII Escape character */
#define ASCII           0x007F  /* Mask ASCII characters  */
#define SBUFSIZ         0x4000  /* Serial buffer size     */

int            SError          = NOERROR;
int            portbase        = 0;
void           interrupt(*oldvects[2])();

static   char  ccbuf[SBUFSIZ];
unsigned int   startbuf        = 0;
unsigned int   endbuf          = 0;


/* Handle communications interrupts and put them in ccbuf */
void   interrupt com_int(void)
{
    disable();
    if ((inportb(portbase + IIR) & RX_MASK) == RX_ID)
    {
        if (((endbuf + 1) & SBUFSIZ - 1) == startbuf)
            SError = BUFOVFL;

        ccbuf[endbuf++] = inportb(portbase + RXR);
        endbuf &= SBUFSIZ - 1;
    }

    /* Signal end of hardware interrupt */
    outportb(ICR, EOI);
    enable();
}

/* Output a character to the serial port */
int    SerialOut(char x)
{
    long int           timeout = 0x0000FFFFL;

    outportb(portbase + MCR,  MC_INT | DTR | RTS);

    /* Wait for Clear To Send from modem */

//    while ((inportb(portbase + MSR) & CTS) == 0)
//      if (!(--timeout))
//	return (-1);

    timeout = 0x0000FFFFL;

    /* Wait for transmitter to clear */
    while ((inportb(portbase + LSR) & XMTRDY) == 0)
        if (!(--timeout))
            return (-1);

    disable();
    outportb(portbase + TXR, x);
    enable();

    return (0);
}

/* Output a string to the serial port */
void   SerialString(char *string)
{
    while (*string)
       SerialOut(*string++);
}

/* This routine returns the current value in the buffer */
int    getccb(void)
{
    int                res;

    if (endbuf == startbuf)
        return (-1);

    res = (int) ccbuf[startbuf++];
    startbuf %= SBUFSIZ;
    return (res);
}

/* Install our functions to handle communications */
void   setvects(void)
{
	switch( portbase ) {
		case COM1BASE:
			oldvects[0] = getvect(0x0C);
			setvect(0x0C, com_int);
			break;
		case COM2BASE:
			oldvects[0] = getvect(0x0B);
			setvect(0x0B, com_int);
			break;
		case COM3BASE:
			oldvects[0] = getvect(0x0D);
			setvect(0x0D, com_int);
			break;
		case COM4BASE:
			oldvects[0] = getvect(0x0D);
			setvect(0x0D, com_int);
			break;
	}
}

/* Uninstall our vectors before exiting the program */
void   resvects(void)
{
	switch( portbase ) {
		case COM1BASE:
			setvect(0x0C, oldvects[0]);
			break;
		case COM2BASE:
			setvect(0x0B, oldvects[0]);
			break;
		case COM3BASE:
			setvect(0x0D, oldvects[0]);
			break;
		case COM4BASE:
			setvect(0x0D, oldvects[0]);
			break;
	}
}

/* Turn on communications interrupts */
void   i_enable(int pnum)
{
    int                c;

    disable();
    c = inportb(portbase + MCR) | MC_INT;
    outportb(portbase + MCR, c);
    outportb(portbase + IER, RX_INT);
	switch( pnum ) {
		case COM1:
			c = inport( IMR ) & IRQ4;
			break;
		case COM2:
			c = inport( IMR ) & IRQ3;
			break;
		case COM3:
			c = inport( IMR ) & IRQ5;
			break;
	}
//    c = inportb(IMR) & (pnum == COM1 ? IRQ4 : IRQ3);
    outportb(IMR, c);
    enable();
}

/* Turn off communications interrupts */
void   i_disable(void)
{
    int                c;

    disable();
    c = inportb(IMR) | ~IRQ3 | ~IRQ4;
    outportb(IMR, c);
    outportb(portbase + IER, 0);
    c = inportb(portbase + MCR) & ~MC_INT;
    outportb(portbase + MCR, c);
    enable();
}

/* Tell modem that we're ready to go */
void   comm_on(void)
{
    int                c, pnum;

	switch( portbase ) {
		case COM1BASE:
			pnum = COM1;
			break;
		case COM2BASE:
			pnum = COM2;
			break;
		case COM3BASE:
			pnum = COM3;
			break;
		case COM4BASE:
			pnum = COM4;
			break;
	}
//    pnum = (portbase == COM1BASE ? COM1 : COM2);
    i_enable(pnum);
    c = inportb(portbase + MCR) | DTR | RTS;
    outportb(portbase + MCR, c);
}

/* Go off-line */
void   comm_off(void)
{
    i_disable();
    outportb(portbase + MCR, 0);
}

void   initserial(void)
{
    endbuf = startbuf = 0;
    setvects();
    comm_on();
}

void   closeserial(void)
{
    comm_off();
    resvects();
}

/* Set the port number to use */
int    SetPort(int Port)
{
    int                Offset, far *RS232_Addr;

    switch (Port)
    { /* Sort out the base address */
      case COM1 : Offset = 0x0000;
                  break;
		case COM2 : Offset = 0x0002;
                  break;
		case COM3 : Offset = 0x0004;
					break;
		case COM4 : Offset = 0x0006;
					break;
      default   : return (-1);
    }

    RS232_Addr = MK_FP(0x0040, Offset);  /* Find out where the port is. */
    if (*RS232_Addr == NULL) return (-1);/* If NULL then port not used. */
    portbase = *RS232_Addr;              /* Otherwise set portbase      */

    return (0);
}

/* This routine sets the speed; will accept funny baud rates. */
/* Setting the speed requires that the DLAB be set on.        */
int    SetSpeed(unsigned int Speed)
{
    char		c;
    int		divisor;

    if (Speed == 0)            /* Avoid divide by zero */
        return (-1);
    else
        divisor = (int) (115200L/Speed);

    if (portbase == 0)
        return (-1);

    disable();
    c = inportb(portbase + LCR);
    outportb(portbase + LCR, (c | 0x80)); /* Set DLAB */
    outportb(portbase + DLL, (divisor & 0x00FF));
    outportb(portbase + DLH, ((divisor >> 8) & 0x00FF));
    outportb(portbase + LCR, c);          /* Reset DLAB */
    enable();

    return (0);
}

/* Set other communications parameters */
int    SetOthers(int Parity, int Bits, int StopBit)
{
    int                setting;

    if (portbase == 0)					return (-1);
    if (Bits < 5 || Bits > 8)				return (-1);
    if (StopBit != 1 && StopBit != 2)			return (-1);
    if (Parity != NO_PARITY && Parity != ODD_PARITY && Parity != EVEN_PARITY)
							return (-1);

    setting  = Bits-5;
    setting |= ((StopBit == 1) ? 0x00 : 0x04);
    setting |= Parity;

    disable();
    outportb(portbase + LCR, setting);
    enable();

    return (0);
}

/* Set up the port */
int    SetSerial(int Port, unsigned int Speed, int Parity, int Bits, int StopBit)
{
    if (SetPort(Port))                    return (-1);
    if (SetSpeed(Speed))                  return (-1);
    if (SetOthers(Parity, Bits, StopBit)) return (-1);

    return (0);
}

/*  Control-Break interrupt handler */
int    c_break(void)
{
    i_disable();
    fprintf(stderr, "\nStill online.\n");

    return(0);
}

main()
{
    /* Communications parameters */
    int        port     = COM3;
    unsigned int speed  = 9600;
    int        parity   = NO_PARITY;
    int        bits     = 8;
    int        stopbits = 1;

    int        c, done  = FALSE;

    if (SetSerial(port, speed, parity, bits, stopbits) != 0)
    {
        fprintf(stderr, "Serial Port setup error.\n");
        return (99);
    }

    initserial();

    ctrlbrk(c_break);

    fprintf(stdout, "TURBO C TERMINAL\n"
		    "...You're now in terminal mode, "
		    "press [ESC] to quit...\n\n");

    /*
       The main loop acts as a dumb terminal. We repeatedly
       check the keyboard buffer, and communications buffer.
    */
    do {
        if (kbhit())
        {
            /* Look for an Escape key */
            switch (c=getch())
            {
                case ESC: done = TRUE;  /* Exit program */
                          break;

                /* You may want to handle other keys here... */
			}
			if (!done)
				SerialOut(c);
        }
        if ((c=getccb()) != -1)
            fputc(c & ASCII, stdout);

    } while (!done && !SError);

    /* Check for errors */
    switch (SError)
    {
        case NOERROR: fprintf(stderr, "\nbye.\n");
                      closeserial();
                      return (0);

        case BUFOVFL: fprintf(stderr, "\nBuffer Overflow.\n");
                      closeserial();
                      return (99);

        default:      fprintf(stderr, "\nUnknown Error, SError = %d\n",
                              SError);
                      closeserial();
                      return (99);
    }
}