New to C programming here so bear with me.. I wrote a program to write/read data to and from the serial port. Everything appears to be working except when I try to read the number of bytes available at the port that have been received. Here's my code (see the read_port function):
#include <stdio.h> /* Standard input/output definitions */
#include <string.h> /* String function definitions */
#include <unistd.h> /* UNIX standard function definitions */
#include <fcntl.h> /* File control definitions */
#include <errno.h> /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */
#include <sys/ioctl.h> /* Serial Port IO Controls */
int fd; /* File descriptor for the port */
struct termios options_original; /* Original Serial Port Options */
int main()
{
fd = open_port();
flush_port();
write_port();
printf("FIONBIO value %d\n", FIONBIO);
usleep(2);
printf("FIONREAD value %d\n", FIONREAD);
read_port();
close_port();
}
/*
* open_port() - Open serial port 1.
*
* Returns the file descriptor on success or -1 on error
*/
int open_port(void)
{
struct termios options;
fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY | O_NONBLOCK);
if (fd != -1)
{
printf("Serial Port Open\n");
fcntl(fd, F_SETFL, 0);
tcgetattr(fd, &options_original);
tcgetattr(fd, &options);
cfsetispeed(&options, B115200);
cfsetospeed(&options, B115200);
options.c_cflag |= (CLOCAL | CREAD); /* Enable the receiver and set local mode */
options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); /* Raw Input Mode */
tcsetattr(fd, TCSANOW, &options); /* Set the new options for the port */
}
else
{
/* Could not open the port */
perror("open_port: Unable to open /dev/ttyUSB0 - ");
}
return (fd);
}
int close_port(void)
{
tcsetattr(fd, TCSANOW, &options_original);
printf("Serial Port Closed\n");
close(fd);
}
int flush_port(void)
{
usleep(2); // required to make flush work, for some reason
printf("Flushing IO Buffers\n");
tcflush(fd, TCIOFLUSH);
}
int write_port(void)
{
int n = write(fd, "DSC", 3);
if (n < 0)
fputs("write() of 1 byte failed!\n", stderr);
else
printf("Wrote %0d bytes to serial port\n", n);
}
int read_port(void)
{
int chars_read = 3;
int bytes;
char read_buffer[3] = {0};
int i;
fcntl(fd, F_SETFL, 0);
ioctl(fd, FIONBIO, &bytes);
printf("Number of bytes = %d\n", bytes);
int n = read(fd, read_buffer, chars_read);
printf("Character at Port: %s\n", read_buffer);
printf("Number of chars read = %0d\n", n);
}
Here's the output:
Serial Port Open
Flushing IO Buffers
Wrote 3 bytes to serial port
FIONBIO value 21537
FIONREAD value 21531
Number of bytes = 0
Character at Port: DSC
Number of chars read = 3
Serial Port Closed
For some reason 'Number of bytes' always equals 0. I have no idea why. Is there something wrong with doing this?
int bytes;
ioctl(fd, FIONBIO, &bytes);
printf("Number of bytes = %d\n", bytes);
It's pretty much verbatim from this site:
http://www.cmrr.umn.edu/~strupp/serial.html#config
Am I missing or not understanding something?
BTW I'm just doing a simple loopback test here.
ioctl(fd, FIONBIO, ...) sets a file descriptor (e.g. a socket) into blocking or
non-blocking mode. What you probably meant is
ioctl(fd, FIONREAD, &bytes);
to get the number of bytes available in the input buffer (i.e. the number of bytes
that can be read without blocking.)
Related
I'm new here.
I'm trying receive data from UART which is from Xbee.
The sample code below is allow me to check the API frame.
But what I need is make these to be a useful array.
How should i make this into a complete array?
The result shows what i need but they are independent.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h> //Used for UART
#include <fcntl.h> //Used for UART
#include <termios.h> //Used for UART
int main(int argc, char const *argv[])
{
//-------------------------
//----- SETUP USART 0 -----
//-------------------------
//At bootup, pins 8 and 10 are already set to UART0_TXD, UART0_RXD (ie the alt0 function) respectively
int uart0_filestream = -1;
//OPEN THE UART
//The flags (defined in fcntl.h):
// Access modes (use 1 of these):
// O_RDONLY - Open for reading only.
// O_RDWR - Open for reading and writing.
// O_WRONLY - Open for writing only.
//
// O_NDELAY / O_NONBLOCK (same function) - Enables nonblocking mode. When set read requests on the file can return immediately with a failure status
// if there is no input immediately available (instead of blocking). Likewise, write requests can also return
// immediately with a failure status if the output can't be written immediately.
//
// O_NOCTTY - When set and path identifies a terminal device, open() shall not cause the terminal device to become the controlling terminal for the process.
uart0_filestream = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY); //Open in non blocking read/write mode
if (uart0_filestream == -1)
{
//ERROR - CAN'T OPEN SERIAL PORT
printf("Error - Unable to open UART. Ensure it is not in use by another application\n");
}
struct termios options;
tcgetattr(uart0_filestream, &options);
options.c_cflag = B9600 | CS8 | CLOCAL | CREAD; //<Set baud rate
options.c_iflag = IGNPAR;
options.c_oflag = 0;
options.c_lflag = 0;
tcflush(uart0_filestream, TCIFLUSH);
tcsetattr(uart0_filestream, TCSANOW, &options);
//----- TX BYTES -----
unsigned char tx_buffer[20];
unsigned char *p_tx_buffer;
p_tx_buffer = &tx_buffer[0];
*p_tx_buffer++ = 'H';
*p_tx_buffer++ = 'e';
*p_tx_buffer++ = 'l';
*p_tx_buffer++ = 'l';
*p_tx_buffer++ = 'o';
if (uart0_filestream != -1)
{
int count = write(uart0_filestream, &tx_buffer[0], (p_tx_buffer - &tx_buffer[0]));
//Filestream, bytes to write, number of bytes to write
if (count < 0)
{
printf("UART TX error\n");
}
}
char r[100];
while(1){
//----- CHECK FOR ANY RX BYTES -----
if (uart0_filestream != -1)
{
//printf("OK");
// Read up to 255 characters from the port if they are there
unsigned char rx_buffer[256];
int rx_length = read(uart0_filestream, (void*)rx_buffer, 255); //Filestream, buffer to store in, number of bytes to read (max)
if (rx_length < 0)
{
//An error occured (will occur if there are no bytes)
}
else if (rx_length == 0)
{
//No data waiting
}
else
{
//Bytes received
rx_buffer[rx_length] = '\0';
printf("%i bytes read : %s\n", rx_length, rx_buffer);
//printf("%d\n",rx_buffer[0]);
}
}
}
return 0;
}
I am trying to read some data from a text file and writing it to the ttyUSB* socket id.
I am using Hi3520d Dvr. I have it's RS485 port connected to a "RS485 to RS232 converter". This converter is connected to the PC through a USB port.
The text file is getting read properly to the buffer, but while writing last few lines of the text is not transmitting. This is happening with file with size more than 4.5kb exactly and without usleep() function.
I am using minicom on linux terminal to display both read and written text.
Thanks in advance for looking into this.
#include <stdio.h>
#include <termios.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#define Bdrate B9600
int Intserial(char *dev, int Baudrate)
{
//printf("Insterial func\n");
int sid;
int iDebug = -1;
struct termios serial_struct;
sid = open(dev, O_RDWR | O_NOCTTY | O_NDELAY);
if (sid > 0)
{
memset(&serial_struct, 0, sizeof(serial_struct)); /* clear the new struct */
serial_struct.c_cflag = Baudrate | CS8 | CLOCAL | CREAD;
serial_struct.c_iflag = IGNPAR;
serial_struct.c_oflag = 0;
serial_struct.c_lflag = 0;
serial_struct.c_cc[VMIN] = 0; /* block untill n bytes are received */
serial_struct.c_cc[VTIME] = 0; /* block untill a timer expires (n * 100 mSec.) */
iDebug = tcsetattr(sid, TCSANOW, &serial_struct);
if (iDebug < 0)
{
printf("Err 0\n"); //Unable to set serial port parameters
return (0);
}
}
else
{
printf("Err 1\n"); //Serial port not open
return (0);
}
//printf("sid is %d \n",sid);
return (sid);
}
int main()
{
int sid1 = -1, size = 0, i = 0, x, w;
size_t ln;
FILE *fd;
char buf[2233];
fd = fopen("h.txt", "r");
if (fd)
{
sid1 = Intserial("/dev/ttyAMA1", Bdrate); //RS485 port of Hi3520d
if (sid1 > -1)
{
system("himm 0x200F004C 0"); // commands transmitting and recieving
system("himm 0x201A0400 1");
system("himm 0x201a0004 1");
while (!feof(fd))
{
memset(buf, 0, sizeof(buf));
fread(buf, sizeof(buf), 1, fd);
printf("%s", buf);
write(sid1, buf, sizeof(buf));
usleep(5);
}
getchar();
}
else
printf("com port cant open\r\n ");
fclose(fd);
close(sid1);
}
else
printf("File cant open\r\n");
printf("task completed............\r\n");
}
You have to observe return value of fread for number of bytes read by fread function. the actual read size may not equal to bytes requested, also you have to pass number of bytes read by fread (as valid bytes in buffer) to write function as number of bytes to write.
The code should be something like this
memset(buf,0,sizeof(buf));
size_t bytesRead = fread(buf,sizeof(buf),1,fd);
if(bytesRead > 0)
write(sid1,buf, bytesRead);
Also as LPs said, fread doesn't end buffer with termination character, so passing buffer filled by fread to printf("%s") will be undefined behavior
There are numerous issues with your code, but the salient cause of "the text is not transmitting" is probably the failure to check the return value of
write(sid1, buf, sizeof(buf));
Because the serial terminal was opened in non-blocking mode, each write() will return immediately, before the data has been actually transmitted.
Since the serial terminal is configured for a rather slow 9600 baud, the data could be queued up in the line discipline buffer and other intermediate buffers.
The line discipline buffer is typically 4096 bytes long.
Assuming that the fread() operations are always successful (which you seem to have verified), then the second iteration of the write() of 2233 bytes could potentially saturate the line discipline buffer, and return with a short write return value (which would be ignored).
The third iteration of the write(), if it's quick enough, could then be outright rejected with a return value of -1 and an errno of EAGAIN to indicate that the write would block.
This error condition would be silently ignored, and this 2233 bytes of data will never be transmitted.
This seems to correlate perfectly with your observation of "last few lines of the text is not transmitting ... with file with size more than 4.5kb exactly and without usleep() function."
ADDENDUM
Revised code for blocking mode, proper terminal setup, and checking of return values is shown below.
A corrected version of #e.jahandar's suggestion and comments from #LPs are also incorporated.
...
sid = open(dev, O_RDWR | O_NOCTTY);
if (sid < 0) {
printf("Err 1\n"); //Serial port not open
return (-1);
}
if (tcgetattr(sid, &serial_struct) < 0) {
printf("Err 2\n");
return (-2);
}
cfsetospeed(&serial_struct, (speed_t)Baudrate);
cfsetispeed(&serial_struct, (speed_t)Baudrate);
cfmakeraw(&serial_struct);
serial_struct.c_cc[VMIN] = 1;
serial_struct.c_cc[VTIME] = 10;
serial_struct.c_cflag &= ~CSTOPB;
serial_struct.c_cflag &= ~CRTSCTS; /* no HW flow control? */
serial_struct.c_cflag |= CLOCAL | CREAD;
if (tcsetattr(sid, TCSANOW, &serial_struct) < 0) {
printf("Err 3\n"); //Unable to set serial port parameters
return (-3);
}
...
#define BUFSIZE 2233
char buf[BUFSIZE + 1];
...
size_t frv;
ssize_t wrv;
...
do {
frv = fread(buf, 1, BUFSIZE, fd);
buf[frv] = 0; /* terminate string for printf */
if (frv > 0) {
wrv = write(sid1, buf, frv);
if (wrv < frv) {
/* handle error or short write */
}
} else
break;
} while (1);
...
I'm writing a simple C program that can read data from a USB port that is connected to my Arduino device. The Arduino outputs data at a baud rate of 9600 in chunks of 4 bytes.
I want the input from the Arduino to my computer to look something like this:
136.134.132.130.129.127.126.124.121.119.117.115.113.111.
However, I'm getting something like this:
271.274.281..2.4062.4022.40225.4021
Question: How do I get the input in my C program to neatly synchronize with out loosing data/ rereading data? Are there some kind of flags that could tell my program when the port has new data?
Code:
#include <stdio.h> /* Standard input/output definitions */
#include <string.h> /* String function definitions */
#include <unistd.h> /* UNIX standard function definitions */
#include <fcntl.h> /* File control definitions */
#include <errno.h> /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */
#include <sys/types.h>
int open_port(void)
{
int fd; /* File descriptor for the port */
fd = open("/dev/tty.usbmodemfd121", O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1)
{
perror("open_port: Unable to open /dev/tty");
}
else
fcntl(fd, F_SETFL, 0);
struct termios options;
tcgetattr(fd,&options);
cfsetospeed(&options,B9600);
options.c_cflag |=(CLOCAL | CREAD);
tcsetattr(fd, TCSANOW, &options);
return (fd);
}
int main (){
int i;
for(i=0; i<50; i++){
fcntl(open_port(), F_SETFL, FNDELAY);
char buf[5];
size_t nbytes;
ssize_t bytes_read;
nbytes = sizeof(buf);
bytes_read = read(open_port(), buf, nbytes);
printf("%s ", buf);
buf[0]=0;
}
return 0;
}
Your program does not properly open() the serial port for reading it.
In fact it repeatedly opens it two times every iteration of the for loop.
The device should be opened only once by your program.
Instead of
for (i=0; i<50; i++) {
fcntl(open_port(), F_SETFL, FNDELAY);
bytes_read = read(open_port(), buf, nbytes);
}
the main program should be structured like
fd = open_port();
if (fd < 0) {
/* handle error condition */
}
rc = fcntl(fd, F_SETFL, FNDELAY);
if (rc < 0) {
/* handle error condition */
}
for (i=0; i<50; i++) {
bytes_read = read(fd, buf, nbytes);
if (bytes_read < 0) {
/* handle error condition */
}
}
close(fd);
Your program is too "simple". It sets only a few attributes, and doesn't bother to check the return codes of system calls.
Is this supposed to be canonical or non-canonical (aka raw) mode (i.e. is the data ASCII text or binary)?
Refer to this Serial Programming Guide for proper setup of the serial port.
read data from a USB port
USB is a bus.
The device your program reads from is a serial port attached to that USBus.
Second coding issue
Your original code may print garbage data.
nbytes = sizeof(buf);
bytes_read = read(open_port(), buf, nbytes);
printf("%s ", buf);
buf[0]=0;
The bytes returned by the read() operation are not likely to be terminated by a NULL byte, so a string operation on that read buffer could exceed the bounds of the allocated array.
Code that would not misbehave would be something like:
nbytes = sizeof(buf) - 1;
bytes_read = read(fd, buf, nbytes);
if (bytes_read < 0) {
/* handle error condition */
} else {
buf[bytes_read] = 0; /* append terminator */
printf("%s ", buf);
}
Note that nbytes is one less than the allocated size of the buffer.
This is to ensure that there is an available byte to store the string terminator byte when the read() operation returns a "full" buffer of nbytes.
For efficiency the assignment of nbytes should be performed before entering the for loop, rather than within the loop.
This question already has answers here:
Reading from a serial port after writing on it
(5 answers)
Closed 8 years ago.
I have written a program in c for reading and writing serial port.But the problem is I am using while loop and it is continuously sending the command over the serial port.
I want to write some command on serial port
wait for answer
write another command
wait for some answer and so on
My code goes like this:-
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <string.h>
#include <errno.h>
#include <time.h>
int main()
{
printf("\n");
printf("Please wait till serial Port is being Initialized .... \n");
sleep(2);
printf("\n................. Initializing ................\n");
sleep(2);
printf("\n");
printf("\n\n");
static int fd = 0;
int len;
char res[100];
char s[100] = " Hellow World";
struct termios options;
//==================================================================
// hard coaded port ttyO3
//==================================================================
fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
fcntl(fd, F_SETFL, O_NONBLOCK);
//==================================================================
// Error Handling
//==================================================================
if (fd < 0)
{
printf("Serial open error %d %s\n", errno, strerror(errno));
}
printf("\n");
printf("\n==================================================\n");
//==================================================================
// Get the current options for the port...
//==================================================================
tcgetattr(fd, &options);
//==================================================================
// Set the baud rates to 115200...
//==================================================================
cfsetispeed(&options, B115200);
cfsetospeed(&options, B115200);
//=================================================================
// Enable the receiver and set local mode..
//==================================================================
options.c_cflag |= (CLOCAL | CREAD);
//==================================================================
// Set the new options for the port...
//==================================================================
tcsetattr(fd, TCSANOW,&options);
while(1)
{
write(fd,s,strlen((char*)s));
sleep(1);
len = read(fd,res,100);
if (len < 0)
{
if (errno == EAGAIN)
{
continue;
}
else
{
printf("read error %d %s\n", errno, strerror(errno));
}
}
else
{
res[len < 100 ? len:100] ='\0';
printf("read %d chars: %s\n",len, res);
}
}
close(fd);
}
where am I getting wrong.
Thanks and Regards
It looks like the file descriptor is opened as non-blocking (fcntl(fd, F_SETFL, O_NONBLOCK);). You must have some blocking operation if you want to wait for data to be read.
You can make the file descriptor blocking, or use some asynchronous manager like select.
Since you make your file descriptor non-blocking (twice), you have to as the system to wait between the steps. A common way to do this is the select system call, which you can use to wait until there is something to read from the file descriptor.
Can be done something like this:
write(...);
fd_set poll_set;
FD_ZERO(&poll_set);
FD_SET(fd, &poll_set);
/* Wait, with no timeout, for something to be readable */
int rc = select(fd + 1, &poll_set, NULL, NULL, NULL);
if (rc == -1)
{
perror("select");
}
else
{
/* Continue to next step, where you read */
}
Also note that the read-calls may actually not receive the complete messages in the first attempt. You may have to read multiple times to get the complete message. If your messages are of a fixed size, then read in a loop while decreasing the amount of bytes to read until you have received the complete message. If your message have a end-of-message marker, then read byte by byte until you receive it. If your messages contain a header with the message size, then use the first fixed-size read method twice, once to get the header and once to get the data.
I am trying to write a C program in Linux to send and receive data from a microcontroller over the serial port. As a test, I have configured the microcontroller to immediately echo all characters sent. I have verified that this works in minicom and also by using "cat" and "echo" to send and receive data.
However, when I try to do the same in a C program, my read call blocks forever. I am setting the serial port to non-canonical mode, with a MIN of '1' and TIME of '0'. My minicom test proves that the microcontroller is returning characters as they are typed, so I expect read to return after the write call has sent characters. I have compared my code to several online examples, and I haven't found anything that I am missing. I have tried several permutations of the code below with no luck. Can someone spot the problem?
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <termios.h>
#define UART_SPEED B115200
char buf[512];
void init_serial (int fd)
{
struct termios termios;
int res;
res = tcgetattr (fd, &termios);
if (res < 0) {
fprintf (stderr, "Termios get error: %s\n", strerror (errno));
exit (-1);
}
cfsetispeed (&termios, UART_SPEED);
cfsetospeed (&termios, UART_SPEED);
termios.c_iflag &= ~(IGNPAR | IXON | IXOFF);
termios.c_iflag |= IGNPAR;
termios.c_cflag &= ~(CSIZE | PARENB | CSTOPB | CREAD | CLOCAL);
termios.c_cflag |= CS8;
termios.c_cflag |= CREAD;
termios.c_cflag |= CLOCAL;
termios.c_lflag &= ~(ICANON | ECHO);
termios.c_cc[VMIN] = 1;
termios.c_cc[VTIME] = 0;
res = tcsetattr (fd, TCSANOW, &termios);
if (res < 0) {
fprintf (stderr, "Termios set error: %s\n", strerror (errno));
exit (-1);
}
}
int main (int argc, char **argv)
{
int fd;
int res;
int i;
if (argc < 2) {
fprintf (stderr, "Please enter device name\n");
return -1;
}
fd = open (argv[1], O_RDWR | O_NOCTTY);
if (fd < 0) {
fprintf (stderr, "Cannot open %s: %s\n", argv[1], strerror(errno));
return -1;
}
init_serial (fd);
res = write (fd, "P=20\r\n", 6);
if (res < 0) {
fprintf (stderr, "Write error: %s\n", strerror(errno));
return -1;
}
tcdrain (fd);
res = read (fd, buf, 512);
printf ("%d\n", res);
if (res < 0) {
fprintf (stderr, "Read error: %s\n", strerror(errno));
return -1;
}
for (i=0; i<res; i++) {
printf ("%c", buf[i]);
}
return 0;
}
You might want to insert some delays, or loop waiting for input.
After setting the bit rate, some types of UART hardware takes one or two characters at the new speed to synchronize to the new speed. It is possible the first few characters are being lost on the write.
After the six character write, the read is issued immediately with a 0.1 second timeout. It is possible that not all the characters from the write() have finished being transmitted before the read(), let alone any time for the remote device to respond.
For example, one solution is:
init_serial (fd);
usleep (100000); // delay 0.1 seconds (Linux) so term parameters have time to change
res = write (fd, "P=20\r\n", 6);
if (res < 0) {
fprintf (stderr, "Write error: %s\n", strerror(errno));
return -1;
}
tcdrain (fd);
usleep (250000); // delay 0.25 for device to respond and return data
res = read (fd, buf, 512);
Another approach would be to continue reading until a sufficient number of characters arrive or a reasonable amount of time passes.