phlayer.c

非常好用的gps数据读写接口

/***************************************************************************
                          phlayer.c  -  physical layer
                             -------------------
    begin                : So M鋜 21 17:50:31 CET 2004
    copyright            : (C) 2004 by Dennis Real
    email                : [e-mail]
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/

#include <sys/types.h>
#include <sys/stat.h> 
#include <sys/termios.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <string.h>
       
#include "phlayer.h" 
#include "def.h"

/*	init tty port
		consider 
			"man 3 termios" and
			"man 2 open" for more information
		returns -1 if error occurs 	*/
int InitTTY (void)
{
	int fd;
	struct termios mytio;                                     
	extern char ttydevice[];

	/* try to get serial port from environment variable */
	if ( getenv("LGGT_SERIAL_PORT")!=NULL )
	{
		strncpy(ttydevice, getenv("LGGT_SERIAL_PORT"), 80);
	}
          
	/* open serial port for reading & writing */
	fd = open(ttydevice, O_RDWR);
  
	if (fd < 0)
	{
    return (-1);
	}

  bzero(&mytio, sizeof(mytio));

	mytio.c_iflag = 0; 
	mytio.c_oflag = ONLRET;
	mytio.c_cflag = B9600 | CS8 | CREAD | CLOCAL | IXON | IXOFF;
	mytio.c_lflag = 0;

	/* forget old unread and unwritten data. now. */
  tcflush(fd, TCIFLUSH);
  tcsetattr(fd, TCSANOW, &mytio);

  return fd;
}


/*	close tty port	*/
void CloseTTY(int iohandler)
{
  close (iohandler);
}


/*	send garminpacket to gps.	*/
void SendPacket(int iohandler, char *gp, unsigned int packetsize)
{
  BYTE i;
  
  for ( i=0; i<packetsize; i++ )
	{
		write (iohandler, &gp[i], 1);
	}

#ifdef DEBUG	
	fprintf(stderr, "Sent %i bytes to gps: \"", packetsize);
/*  for (i = 0; i<packetsize; i++)
  {
		fprintf(stderr, "%c", (BYTE)gp[i]);
	}
	fprintf(stderr, "\"\n");*/
	
  for (i = 0; i<packetsize; i++)
  {
		fprintf(stderr, "%02x ", (BYTE)gp[i]);
	}
	fprintf(stderr, "\n\n");
#endif
  
}


/*	read from tty until 0x10 ... !0x10 0x10 0x03 received or timeout	*/
char *GetPacket(int iohandler, unsigned int *size)
{  
	static char buffer [READBUFFER];
	char ch=0, last=0;
	int t=0;
	int counted;
	int i=0, j;

	do
	{
		/* data available? */
		ioctl(iohandler, FIONREAD, &counted);

		last=ch;

		if ( counted!=0 )
		{
			/* data available! */
			if (read (iohandler, &ch, 1) != 1)  
			{
				fprintf(stderr, "Error: Reading tty failed. Exiting...\n");
				exit(-1);
    	}
    	else
    	{
    		/* 1 byte read */
				t=0;

				/* a valid packet must start with 0x10 */
				if ( (i==0) && (ch!=0x10) )
				{
//fprintf(stderr, "trashed %02x\n", (unsigned char)ch);					
				}
				else 
				{
					if ( i < (READBUFFER-1) ) 
					{
						buffer[i++]=ch;
					}
					else
					{
						fprintf(stderr, "Error: Receive buffer full. Exiting...\n");
						exit(-1);
					}
				}
				
				if ( (i==2) && ((ch==0x03) || (ch==0x10)) )
				{
					/* DTE (10) & ETX (3) will never be a packet id. */
//fprintf(stderr, "trash! %02x\n", (unsigned char)ch);										
					i=0;
					t=0;
					ch=0;
					last=0;

				}	
			}


			/*	DLE stuffing: A DLE character (0x10) in size, packet data
					or checksum will be followed by another DLE. Remove it
					in link layer later but take care of complete packet here.	*/ 
			if ( (last==0x10) && (ch==0x10) )
			{
				last=0;
			}
		}
		else
		{
			/* no data available */
			
			usleep(10000);
			if ( t++ >= READTIMEOUT )
			{
				fprintf(stderr, "Warning: Timeout while reading from tty.\n");
				*size=0;
				//exit(-1);
				return NULL;
			}
		}

  } while ( !((ch==0x03) && (last==0x10)) || (i<5) );

 	buffer[i]='\0';

	*size=(unsigned int)i;

#ifdef DEBUG  
  fprintf(stderr, "Received %i bytes from tty: \"", i);
/*  for ( j=0; j<i; j++)
  {
		fprintf(stderr, "%c", (BYTE)buffer[j]);
	}
	fprintf(stderr, "\"\n");*/
	
  for ( j=0; j<i; j++)
  {
		fprintf(stderr, "%02x ", (BYTE)buffer[j]);
	}
	fprintf(stderr, "\n\n");
#endif

  return (buffer);
}