INTERRUPT DRIVEN SERIAL COMMUNICATIONS 

 Technical Information Database

TI106C.txt   INTERRUPT DRIVEN SERIAL COMMUNICATIONS            
Category   :General
Platform    :All
Product    :Turbo C  1.0 & 1

Description:
  /*-------------------------------------------------------------*
                              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 com-
     munications 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 "serial.h"
  #include 
  #include 
  #include 
  #include 
  #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)
  {
      oldvects[0] = getvect(0x0B);
      oldvects[1] = getvect(0x0C);
      setvect(0x0B, com_int);
      setvect(0x0C, com_int);
  }
  /* Uninstall our vectors before exiting the program */
  void   resvects(void)
  {
      setvect(0x0B, oldvects[0]);
      setvect(0x0C, oldvects[1]);
  }
  /* 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);
      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;
      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;
        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(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)                                  r e t urn
  (-1);
      if (Bits < 5 || Bits > 8)                           r e t urn
  (-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);