Problem to write to serial port

os2 · 12-02-2004, 01:24 PM

hi

under linux, i try to write to serial port who pluged to a monitor (del monitor)

with bash i do

Code:

echo -e \\000\\000\\000\\000\000\\001Z00\\002AA Keg Marty is in the house\\004 >/dev/ttyS2

that work fine.. Keg Marty is in the house is displayed on the panel

i would like to do the same thing in C

my c program (compile well... but don't work)

Code:

#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
int main (void)
{
  int iOut = 0;
  int fd = 0;
  char *sCompPort="/dev/ttyS2";
  //char cmd[70];
  char cmd[]="\\000\\000\\000\\000\000\\001Z00\\002AA Keg Marty is in the house\\004";

  fd = open(sCompPort, O_RDWR | O_NOCTTY);

  if (fd >0){
    printf("port open");

    iOut = write(fd, cmd, strlen(cmd));
    close(fd);
   }
   else{
     printf("not able to open port.");
   }

   if (iOut > 0){
     printf("no commmunication.");
   }
   else{
     printf("good Communication");
   }
   return (0);
}

return me port open and no communication...

any idea?

bastard23 · 12-02-2004, 11:34 PM

write() returns the number of bytes and -1 on error. So if (iOut >0) is backwards.

if (iOut < 0){
printf("no commmunication.");
}
else{
printf("Wrote %d of %d bytes", iOut, sizeof(cmd));
}
return (0);

Second, you don't need the double backslashes on your string (\\001), just one (\001). And remember it's octal, so use \xnn when you mean hex. You need the double backslash on the echo command because the shell interprets the backslash as well.

randyding · 12-03-2004, 07:17 PM

There's one more issue with that example code, the cmd[] array begins with a \0, so strlen() can't be used to calculate the number of bytes to transmit in the write() function. Previous poster correctly said sizeof(cmd) would work, but I think it should be sizeof(cmd)-1 to be most accurate, the compiler includes the implicit termination null in sizeof() a char array.

os2 · 12-22-2004, 10:59 AM

with this code,

Code:

#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
int main (void)
{
  int iOut = 0;
  int fd = 0;
  char *sCompPort="/dev/ttyS2";
  //char cmd[70];
  //echo -e \\000\\000\\000\\000\000\\001Z00\\002AA LINUX \\004 >/dev/ttyS2
  
  char cmd[]="\\000\\000\\000\\000\\000\\001Z00\\002AA linux \\004";
  //return
  //port open
  //strlen(cmd) 43
  //Wrote 43 of 43 bytes
  
  //char cmd[]="\000\000\000\000\000\001Z00\002AA linux\004";
  //return
  //port open
  //strlen(cmd) 0
  //Wrote 0 of 19 bytes
  
  fd = open(sCompPort, O_RDWR | O_NOCTTY);

  if (fd >0){
    printf("port open\n");
    printf("strlen(cmd) %d\n",strlen(cmd) );
    iOut = write(fd, cmd, strlen(cmd));
    close(fd);
   }
   else{
     printf("not able to open port.\n");
   }

   if (iOut < 0){
     printf("no commmunication.\n");
   }
   else{
     printf("Wrote %d of %d bytes\n", iOut, sizeof(cmd)-1);
   }
   return (0);
}

data was sending to the serial port... the port is connected to a display pannel...
there are some code to initialize the connection, centering the text, close connection... in bash mode that work fine... but not in this c program...
nothing is interpreted... all is displayed to the display pannel...

any idea?

shmonkey · 12-22-2004, 02:11 PM

How exactly are you compiling the program ?

os2 · 12-22-2004, 02:37 PM

Quote:

Originally posted by shmonkey
How exactly are you compiling the program ?

my makefile

Code:

CC= /opt/cross-ppc/bin/powerpc-855-linux-gnu-gcc-3.3
DEFS=
PROGNAME= moniteur
INCLUDES=
LIBS=

# replace -O with -g in order to debug

DEFINES= $(INCLUDES) $(DEFS)
#CFLAGS= -g -Wall $(DEFINES)
CFLAGS= -O -Wall $(DEFINES)

SRCS = moniteur.c

OBJS = moniteur.o

.c.o:
        rm -f $@
        $(CC) $(CFLAGS) -c $*.c

all:    $(PROGNAME)

$(PROGNAME) :   $(OBJS)
        $(CC) $(CFLAGS) -o $(PROGNAME) $(OBJS) $(LIBS)
        cp $(PROGNAME) /opt/good/bin

clean:
        rm -f $(OBJS) $(PROGNAME) core