On Feb 20, 3:06 pm, MVennebu...@web.de wrote:
Quote:
Hi,
>
I want to read/parse the binary output of a GPS receiver written to
the serial interface. The data packages start with a "$@".
>
The following program does read from the serial interface, but it does
not find the beginning of a data block. (I am very sure that the
binary data sent from the GPS receiver does contain the "$@"!). So
there must be an error in the if-statement. Do I have to cast either
"buf[0]" or the '$'-sign? What else could be wrong?
As the snippet that follows uses POSIX headers and functions, your
question(s) belong in another newsgroup, namely comp.unix.programmer.
comp.lang.c discusses ISO C and ISO C only.
<bellow is OT>
Quote:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
>
#define BAUDRATE B38400
This doesn't seem valid..
Quote:
#define MODEMDEVICE "/dev/ttyS0"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
Rather annoying macros IMHO.
Quote:
#define BLOCKSIZE 1
Since you won't change this (or else, your whole code would change as
seen bellow)
why not write a readbyte(sock, buf) function instead? (or just use
read with 1 as size)
Quote:
int main()
{
int fd;
struct termios oldtio,newtio;
char buf[BLOCKSIZE];
>
ssize_t res;
>
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) { printf("ERROR while opening MODEMDEVICE \n");
perror(MODEMDEVICE); return 0; }
>
tcgetattr(fd,&oldtio); /* save current port settings */
>
bzero(&newtio, sizeof(newtio));
bzero marked as a legacy function from the open group base spec issue
6.
(available online at <http://www.opengroup.org/onlinepubs/009695399/>)
Use memset(&newtio, 0, sizeof newtio); instead, or the macro suggested
by open group.
Quote:
#define bzero(b,len) (memset((b), '\0', (len)), (void) 0)
Quote:
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
You have defined BAUDRATE as B38400, that would probably be a syntax
error.
Quote:
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
>
/* set input mode (non-canonical, no echo,...) */
newtio.c_lflag = 0;
>
newtio.c_cc[VTIME] = 0; /* inter-character timer unused */
newtio.c_cc[VMIN] = 5; /* blocking read until 5 chars received
*/
>
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
>
while (1) {
>
res = read(fd, &buf, BLOCKSIZE);
Why don't you check the return value of read?
Why set it every time you run the loop?
Quote:
>
printf("%c\n", buf[0]);
// Why does the following not work???
if (buf[0] == '$') { printf("Possible beginning of data!\n");
Possibly? that is not reliable at all. Have a size_t object that
counts the data that has been read.
if(buf[0] == '$' && count == 0) /* possibly beginning of data */
Quote:
sleep(1); }
// read next byte and check for "@"...
Do you really want to sleep there?
It is very likely that you have not posted the code that doesn't
"work".
