waitquie.c

异步通讯C语言例行子程序

/* A module of ASYNCx.LIB version 1.10 */

#include <dos.h>
#include "asyncdef.h"

/*
** Wait for between t and t+1 18ths of a second to elapse without any
** characters arriving at port p. If max 18ths of a second elapse before
** a gap in the incomming data of t 18ths of a second has been found, a
** value of -1 is returned. If the gap is found within max 18ths of a
** second, a value of 0 is returned. If mode is set to 0, any characters
** that do arrive during the execution of this routine are discarded and
** the input buffer for the port p is empty when this routine returns.
** If mode is set to 1, characters arriving at the port are detected but
** not discarded. Be careful of buffer overflow if use mode 1. If the
** input buffer overflows, the least recent data will be lost and the
** newest data will be retained.
*/
int a_waitquiet(ASYNC *p,int t,int max,int mode)
{unsigned long t0,t1,far *t2;
 int count0;
 if (!p)
   return -1;
 /*
 ** *t2 is the current time and is incrimented by the operating system
 ** 18.21 times per second.
 */
 t2=(unsigned long far *)MK_FP(0x40,0x6c);
 /*
 ** t0 is the initial time. t1 is the time at which the last character
 ** was received. (Assume that a character was just received.)
 */
 t0=t1=*t2;
 if (mode==0)
   while ((*t2)-t1<=(unsigned long)t && (*t2)-t0<=(unsigned long)max)
    {if (a_getc(p)!=-1) /* If another character has been received, */
       t1=*t2;          /* update t1.                              */
    }
 else
  {count0=a_icount(p);            /* count0 = # of chars in buffer   */
   while((*t2)-t1<=(unsigned long)t && (*t2)-t0<=(unsigned long)max)
     if (a_icount(p)!=count0)     /* If more characters are received */
      {t1=*t2;                    /* update t1 and                   */
       count0=a_icount(p);        /* the character counter.          */
      }
  }
 if ((*t2)-t1>=(unsigned long)t)
   return 0;
 else
   return -1;
} /* end of int a_waitquiet(p,t,max,mode) */