Problem with string and serial port

collinm · 03-22-2005, 11:00 AM

hi

in c programming (linux), i search a way to read the setting of the serial port (speed, parity...) and change it.

i need also to write to a led display (alpha sign communications protocole)

with bash i do:

Code:

echo -e \\000\\000\\000\\000\\000\\001Z00\\002AA Triplex\\004 >/dev/ttyS2

my source code

Code:

#include <sys/ioctl.h>
#include <stdio.h>
#include <stdlib.h>                     /*atoi, system, getenv */
#include <unistd.h>                     /*sleep, close */
#include <dirent.h>                     /*opendir, readdir, closedir */
#include <string.h>
#include <fcntl.h>                      /*open */
#include <sys/stat.h>
#include <sys/errno.h>  

char *ledisplay;

/* Opening port one for read and write */
int writeopen(char msg[])
{
    int fd1;
    int wr;
    fd1 = open(ledisplay, O_RDWR | O_NOCTTY | O_NDELAY );
    if (fd1 == -1)
    {
        fprintf(stderr, " %s open_port: Unable to open %s\n", strerror(errno), ledisplay);
    }
    else
    {
        fcntl(fd1, F_SETFL, 0);
        printf(" Port 1 has been sucessfully opened and %d is the file descriptor\n",fd1);
        
        printf("sizeof %d\n", sizeof(msg));
        
        wr=write(fd1, msg, sizeof(msg));
        printf(" Bytes sent are %d \n",wr);
        if (wr < 0)
            fputs("write() of n bytes failed!\n", stderr);
        else
            printf(" Stuff has been written into port 1\n");
        close(fd1);
    }
    return (fd1);
} 

int readopen()
{
    int fd1;
    int rd;
    char *buff=NULL;
    fd1 = open(ledisplay, O_RDONLY | O_NOCTTY | O_NDELAY );
    if (fd1 == -1)
    {
        fprintf(stderr, "%s open_port: Unable to open %s\n", strerror(errno), ledisplay); 
    }
    else
    {
        fcntl(fd1, F_SETFL, 0);
        printf(" Port 1 has been sucessfully opened and %d is the file descriptor\n",fd1);
        rd=read(fd1, buff, 100);
        printf(" Bytes recieved are %d \n",rd);
        printf("%s\n",buff);
        close(fd1);
    }
    return (fd1);
} 

int main()
{
    int result;
    
    //echo -e \\000\\000\\000\\000\000\\001Z00\\002AA TRIPLEX \\004 >/dev/ttyS2
    char msg[] = {'\0', '\0', '\0', '\0', '\0', '\1', 'Z', '0', '0', '\2', 'A', 'A', ' ', 'T', 'R', 'I', 'P', 'L', 'E', 'X', ' ', '\4' };
  
    if((result=(readRtuConfig()))!=-1)
    {
    
        printf("port série utilisé: %s\n", ledisplay);
        printf("msg = %s\n",msg);

         if((result=(writeopen(msg)))!=-1)
         {
            printf("ok\n");
         }
    }
    return 1;
}

when i run this program i get

Code:

Port 1 has been sucessfully opened and 3 is the file descriptor
Bytes sent are 4
Stuff has been written into port 1
ok

that seem ok but on the led display, i see nothing...

surely,
char msg[] = {'\0', '\0', '\0', '\0', '\0', '\1', 'Z', '0', '0', '\2', 'A', 'A', ' ', 'T', 'R', 'I', 'P', 'L', 'E', 'X', '\4' };

is not equivalent to this bash command

echo -e \\000\\000\\000\\000\\000\\001Z00\\002AA Triplex\\004 >/dev/ttyS2

any idea?

swoopy · 03-22-2005, 01:54 PM

>Bytes sent are 4
Notice you're only writing out 4 bytes to your port, even though your message is much longer. Once you pass an array to a function, all you get is the size of a pointer. You need to pass the size of the array to the function:

Code:

         if((result=(writeopen(msg, sizeof(msg))))!=-1)

Or you could wrap the array in a struct.

I don't know bash, so I can't tell you whether msg matches what you are sending using bash. If you can tell us what bash actually sends, then we can tell you what msg should be.

tjohnsson · 03-23-2005, 10:19 AM

There's tcgetattr (...) what you can use to get serial configuration...
"man termios" gives you more information about it and there's
Serial-Programming-HOWTO in tldp.org...

If your schedule is busy enough, hit "setserial" on your console,
read quick info and do what you need to.

03-22-2005, 01:54 PM	#2
swoopy Registered User Join Date: Oct 2001 Posts: 2,936	>Bytes sent are 4 Notice you're only writing out 4 bytes to your port, even though your message is much longer. Once you pass an array to a function, all you get is the size of a pointer. You need to pass the size of the array to the function: Code: if((result=(writeopen(msg, sizeof(msg))))!=-1) Or you could wrap the array in a struct. I don't know bash, so I can't tell you whether msg matches what you are sending using bash. If you can tell us what bash actually sends, then we can tell you what msg should be. __________________ http://www.freechess.org
swoopy is offline

03-23-2005, 10:19 AM	#3
tjohnsson SleepWalker Join Date: Apr 2004 Posts: 70	There's tcgetattr (...) what you can use to get serial configuration... "man termios" gives you more information about it and there's Serial-Programming-HOWTO in tldp.org... If your schedule is busy enough, hit "setserial" on your console, read quick info and do what you need to. __________________ -- Add Your Signature Here --
tjohnsson is offline

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