Reading data from serial port

[anu29dolly]

Hello everyone...

I have written a program to write and read data from serial port....
I am able to write 80(in binary)..and is expecting 1B but i am uable to read it...

My code goes as follows,,....

 
int main()
 
{
 
int mainfd=0;
 
 
 
 
mainfd = open_port();
close(mainfd);
 
fd = open( "/dev/ttyS0" ,O_RDWR |O_NOCTTY | O_NDELAY);
if (fd == -1) {
perror("open_port: Unable to open /dev/ttyS0 - ");
return 1;
} else {
fcntl(fd, F_SETFL,0);
}
/* Clear the line */
tcflush(fd,TCIFLUSH);
 
initport(fd);
 
 
char sCmd[1];
sCmd[0] =0010;//0010;
sCmd[1] =0000;//0000;
 
if (!writeport(fd, sCmd)) {
printf("write failed\n");
close(fd);
return 1;
}
 
 
printf("written: %d%d\n", sCmd[0],sCmd[1]);
close(fd);
 
usleep(30000);
fd = 0;
fd = open( "/dev/ttyS0" ,O_RDONLY |O_NOCTTY | O_NDELAY);
char sResult[1];
fcntl(fd, F_SETFL, FNDELAY); // don't block serial read
 
if (!readport(fd,sResult)) {
printf("read failed\n");
close(fd);
return 1;
}
else
close(fd);
return 0;
}
 
 
the read write functions are as follows....
 
 
int fd;
char iIn[1];
 
int open_port (void)
{
 
 
int ser_cmd, ser_stat;
ser_cmd = TIOCM_RTS;
 
fd = open("/dev/ttyS0", O_RDONLY); // Open the serial port.
 
if (fd == -1)
{
perror("open_port: Unable to open /dev/ttyS0 -%s\n "); 
return 1; 
} else{
printf("Port 0 opened\n");
fcntl(fd, F_SETFL, 0);
}
 
// Read the RTS pin status.....
 
ioctl(fd, TIOCMGET, &ser_stat);
if (ser_stat & TIOCM_RTS)
{
printf("RTS pin is set.\n");
}
else
{
printf("RTS pin is reset.\n");
ioctl(fd, TIOCMBIC, &ser_cmd); // set the RTS pin.
if (ser_stat & TIOCM_RTS)
printf("RTS pin is set.\n");
else
printf("RTS pin is reset.\n");
 
}
return (fd);
}
 
 
 
 
int writeport(int fd, char *chars) 
 
{
int len =strlen(chars);
 
int n = write(fd, chars,strlen(chars));
if (n < 0)
{
fputs("write failed!\n", stderr);
 
return 0;
}
fcntl(fd, F_SETFL,0);//changed
return 1;
}
 
int readport(int fd, char *result) {
int iIn = read(fd, result, 1);
printf("Value Received: %x\n",*result);
 
 
return 1;
}
 
 
**************************************
here it gives 40...
************************************
int initport(int fd){
 
struct termios options;
printf("Setting Parameters...\n");
tcgetattr(fd, &options);
cfsetispeed(&options, B9600); /* Set the baud rates to 9600 */
cfsetospeed(&options, B9600);
 
/* Enable the receiver and set local mode */
options.c_cflag |= (CLOCAL | CREAD);
options.c_cflag &= ~PARENB; /* Mask the character size to 8 bits, no parity */
options.c_cflag &= ~CSTOPB;
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8; /* Select 8 data bits */
options.c_cflag &= ~CRTSCTS; /* Disable hardware flow control */ 
 
/* Enable data to be processed as raw input */
options.c_lflag &= ~(ICANON | ECHO | ISIG);
 
options.c_cc[VMIN]=0;//it will wait for one byte at a time.
options.c_cc[VTIME]=10;// it will wait for 0.1s at a time.
/* Set the new options for the port */
tcsetattr(fd, TCSANOW, &options);
printf("Parameters SET!!!...\n");
return 1;
}
 

[gpraghuram]

Hi,
whenever you are reading froma serial port try to read in chunks.
After reading a certain chunk check whther you have read desired bytes or else read the remaining bytes.
Do this in a loop always.

Thanks
Raghu

[anu29dolly]

okk but can u plz guide me how to do this...
can u suggest modifications for the same in my program...

thanks
in advance

[gpraghuram]

I have made some changes to the code . I wont say that this is perfectly right and this is only to make you understand the idea

 
int readport(int fd, char *result) 
{ 
//Have a while loop here
int lnReadLength=0;
while(lnReadLength <= 100)//I am assuming u want to read 100 bytes
{
int iIn = read(fd, result, 10); 
lnReadLength += iln;
result = (result+lnReadLength);
}
//printf("Value Received: %x\n",*result); 
return 1; 
} 
 

Raghu

[anu29dolly]

ya thank you very much...for ur help...

i hope u read my code i think i making a mistake in writing the data..as i mentioned that i have to send 80(hex value) to the serial port and then read..

i think the write function is not working and hence the read function...

the write function i am pasting again...........
can u plz have a look at it and confirm its correctness...

thanks

code as follows...

...
...
int main()
{

...
...
...

initport(fd);

int sCmd[1];

sCmd[0]=0200;

(this value is gives given in octal as we cannot give 80 in hex directly...
and serial port accepts only hex or octal values)



if (!writeport(fd, sCmd)) {
printf("write failed\n");
close(fd);
return 1;
}

printf("written: %x\n", sCmd[0]);
close(fd);

************************************************** ***********************
and this is the writeport function.....




int writeport(int fd, char *chars)

{
int len =strlen(chars);

int n = write(fd, chars,strlen(chars));
if (n < 0)
{
fputs("write failed!\n", stderr);

return 0;
}
fcntl(fd, F_SETFL,0);//changed
return 1;
}

[gpraghuram]

i think u shuld follow the same approach like writing in chunks and then return the status.

Thanks
Raghu

[anu29dolly]

i have tried that but dnot know the program is not reading data from port...now it is writing correctly....

can u please guide me..

thanks