Hello all,

I have a small program which should be writing on to the serial port. I send a 'space' character and the device connected to the serial port returns '>' as an acknowledgement.

With the same setting(serial port settings of my program) if i try to send a space character with another readymade program i get an ackowledgement without any issue.

But somehow my writes are not reaching the device i believe. Is there anything that i need to flush?
I have put a sniffer(portmon) and watching whats happening and I see that it says 1 character written successfully, although this does not guarantee that it has reached the device properly because, even if the serial port cable is dangling without any connection to the extenral device, i get a message saying the write was successful.

Below is my program. Could anyone please let me know what am I doing wrong here?

#include<unistd.h>
#include<fcntl.h>
int main(void)
{
int fd=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
fcntl(fd,F_SETFL,0);
unsigned char sim = 0x20;
write(fd,&sim,1);
char *bfr=new char[255];
read(fd,bfr,1);
}
As the write has not yet reached the device, the read continuosly blocks!!!
Any clue on whats hapening.
I am trying this on cygwin. But i tried this on red hat linux enterprise 4, with the same result. The strange part is, when i started out to write this program, it was working perfectly fine on cygwin, with data being sent and recvd, but when i started adding extra code to it(like setting serial attributes etc), at some point it broke down and its not recovering

Please help!

i am stuck with this from the past 2days. any pointers would be of great help. even if its a weblink i am ready to read and implement

thanks again

Try d/l my serial utils .c and .h file. Its too large to post here.

can you not start commenting out you modifications until you get to the point where it starts working again,then go forward making small change at a time trying to pin point which line of new code breaks it.
Sorry only thing I can sugest

Ok 2 problems here in this code

1. you have no return statement use int for main with return 0;
2. You are declareing the char incorrectly.

char *bfr=new char[255];

This doesent compile with gcc under linux.

you should define all of your variables before making function calls. But that is not whats wrong with the char. it should be in 2 parts.

char *bfr;
char new[255];

hey exvor..
thanks for the response...but this is c++, sorry i didnt tell u that before..
1) return statement is not necessary. cuz it compiled without issues.
2) dynamic allocation.

slzckboy

i tried dat. no use. it still fails

randyding

i will take a peek at it.

any help..anyone. i am still stuck

Test the return values of functions like 'open' and 'write' and print them, so you can see what happens.

Compiling without issues probably means that you don't have all warnings on.

And the fact that you can't go back more-than-likely means that your HW is in an undefined state somewhere.

If of interest, I posted a setup function for RS232 in this thread

I felt the urge to respond back
There was nothing wrong with the program that I wrote to begin with. It seems the serial device that I am connecting to needs a wait period of 1.6milliseconds before it starts responding to my characters. I did not give a breathing 'space' to the poor guy.
Now things are fine. Thanks a lot for all your help.

Cheers,
Kiran

Yea i figured it was some C++ crazyness :P but dident know if it was diffrent in that language.