cannot properly read data string using windows serial in windows.h - c

i have a microcontroller connected to my usb port which i am reading using the code below
`
#include <windows.h>
#include <stdio.h>
#include <conio.h>
int main (void)
{
int n = 25;
char szBuff[25 + 1] = {0};
HANDLE hSerial;
DCB dcbSerialParams = {0};
COMMTIMEOUTS timeouts={0};
DWORD dwBytesRead =25;
dcbSerialParams.DCBlength=sizeof(DCB);
hSerial = CreateFile("COM4",
GENERIC_READ | GENERIC_WRITE,
0,
0,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
0);
if(hSerial==INVALID_HANDLE_VALUE)
{
if(GetLastError()==ERROR_FILE_NOT_FOUND)
{
puts ("cannot open port!");
return;
}
puts ("invalid handle value!");
return;
}
if (!GetCommState(hSerial, &dcbSerialParams))
{
puts ("error getting state");
return;
}
dcbSerialParams.BaudRate=CBR_57600;
dcbSerialParams.ByteSize=8;
dcbSerialParams.StopBits=ONESTOPBIT;
dcbSerialParams.Parity=NOPARITY;
if(!SetCommState(hSerial, &dcbSerialParams))
{
puts ("error setting port state");
return;
}
timeouts.ReadIntervalTimeout = 30;
timeouts.ReadTotalTimeoutMultiplier = 100;
timeouts.ReadTotalTimeoutConstant = 100;
if (!SetCommTimeouts(hSerial, &timeouts))
{
puts ("timeouts setting fail!");
}
while (1){
if(!ReadFile(hSerial, szBuff, n, &dwBytesRead, NULL)){
puts ("serial read error fail!");
return;
}
else
{
printf ("%s\n" , szBuff);
}
}
getch();
return 0;
}
`
i am sending data by this format: $A.B.C$ followed by a newline. so its 7 (or 8, including newline) bytes right? i set the 3rd argument for readfile to 20, greater than 7 bytes so that i can succesfully read all of the data string. however reading sometimes misses a few characters. instead of reading $A.B.C$ i read in one line $A.B.C and in the line after that $ (a hidden'\n'). how can i fix this?

This is normal. When the receive buffer contains at least one byte, you'll get back whatever is in the buffer. Which is usually but a fraction of what you expect, serial ports are quite slow. You'll have to keep reading until you get the full response.

Just to add to the answer, be sure to use some type of timeout, or you will block waiting a character that maybe never comes.
Maybe one option could be reading byte per byte then just wait the last '$' or '\n' to know that you received the complete string and then process it.

Related

How can I get data from a GPS module coming with NMEA protocol through a Serial port with c

I need to get data from a GPS module which is coming in NMEA protocol through a Serial port, and the input looks something like this:
$GPRMC,190335.389,V,3754.931,N,08002.496,W,33.6,0.59,110619,,E*47
$GPGGA,190336.389,3754.931,N,08002.496,W,0,00,,,M,,M,,*52
$GPGLL,3754.931,N,08002.496,W,190337.389,V*33
$GPVTG,0.59,T,,M,33.6,N,62.2,K*5C
$GPRMC,190339.389,V,3754.932,N,08002.494,W,11.9,0.62,110619,,E*4D
$GPGGA,190340.389,3754.932,N,08002.494,W,0,00,,,M,,M,,*52
$GPGLL,3754.932,N,08002.494,W,190341.389,V*33
The thing is, I only need the lines starting with GPRMC. And the problem is the data is coming asynchronous, first comes the first half of a line, for example, then the other half and some of the other line and so on. Now how can I get the input line-by-line and only get the ones starting with GPRMC. The input is coming incessant and I need to get the correct line real-time. How could I do this with C?
I don't really know how to read from a Serial port, I tried something but because the input's coming asynchronous, I couldn't get the correct lines. Oh, and one more thing, the maximum length of a line is 83.
Here's some code I tried, I know it's bad
int a = 0;
int test = 0;
int gprmc_find(char* gps)
{
while(a < strlen(gps))
{
if(gps[a] =='$' && gps[a+1] == 'G' && gps[a+2] == 'P' && gps[a+3] == 'R' )
{
test = 1;
break;
}
else
{
test = 0;
}
a++;
return test;
}
}
int main()
{
DWORD accessdirection =GENERIC_READ | GENERIC_WRITE;
HANDLE hSerial = CreateFile("COM4",
accessdirection,
0,
0,
OPEN_EXISTING,
0,
0);
if (hSerial == INVALID_HANDLE_VALUE) {
printf("Invalid\n");
}
DCB dcbSerialParams = {0};
dcbSerialParams.DCBlength=sizeof(dcbSerialParams);
if (!GetCommState(hSerial, &dcbSerialParams)) {
printf("could not get the state of the comport\n");
}
dcbSerialParams.BaudRate=9600;
dcbSerialParams.ByteSize=8;
dcbSerialParams.StopBits=ONESTOPBIT;
dcbSerialParams.Parity=NOPARITY;
if(!SetCommState(hSerial, &dcbSerialParams)){
printf("Error\n");
}
COMMTIMEOUTS timeouts={0};
timeouts.ReadIntervalTimeout=50;
timeouts.ReadTotalTimeoutConstant=50;
timeouts.ReadTotalTimeoutMultiplier=10;
timeouts.WriteTotalTimeoutConstant=50;
timeouts.WriteTotalTimeoutMultiplier=10;
if(!SetCommTimeouts(hSerial, &timeouts)){
printf("handle error1");
}
char buf[83] = {0};
while(1)
{
DWORD dwBytesRead = 0;
//CloseHandle(hSerial);
if(!ReadFile(hSerial, buf, 82, &dwBytesRead, NULL)){
printf("handle error");
}
printf(" %d \n", test);
if(gprmc_find(buf) == 1)
{
printf(buf);
}
memset(buf, 0, 83);
delay(1);
}
return 0;
}
GPS NMEA 0183 is a text-based protocol and can be processed with a platform-independent C language standard library.
Many libraries and parsers have already been developed, and you can use them without redevelopment.
For example, you can find this article on the StackOverflow site:
NMEA library - nmeaINFO empty / NMEA Library
C Gps nmea parser from linux serial port does not parse the last line of the read buffer
Parsing code for GPS NMEA string
Other site:
MULTI-PLATFORM SERIAL INTERFACING USING BOOST: A GPS SENSOR AND OPENDDS - PART I / PART II
These are parsers, libraries that parse the read data.
jacketizer/libnmea
kosma/minmea
MaJerle/GPS_NMEA_parser
After analyzing in the above library, you should use only the data you want.

Entire characters in the text file is not getting transmitted in Hi 3520D

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);
...

Connecting two serial ports in C

I want to connect/bridge two serial ports in C.
I have 2 threads reading the ports, and writing to the other port.
Here is one example:
void *rfid_to_uart_thread(void *) {
char rfid_read_buffer[100];
int writeCounter;
do {
writeCounter = read(rfidCom, rfid_read_buffer, sizeof(rfid_read_buffer)-1);
if (writeCounter > 0) {
write(uartCom, rfid_read_buffer, writeCounter);
} else
usleep(25);
} while (!bKillBridgeThreads);
return NULL;}
The problem is, it seems that the writes are too slow. I often receive only half of the String on the other side. It seems like the write is asynchronously and thus the buffer is overwritten again in the next loop and overwrites the last 'write', so that the data is crippled?!
Is that right?
The ports are opened NON_BLOCKING and RW, Baudrate is and has to be 9600.
Looking at the man:
read() attempts to read up to count bytes from file descriptor fd into the buffer starting at buf.
In other wordsread does not grants to return all bytes send by other task, can give you a single byte up to sizeof(rfid_read_buffer)-1
What you can do is:
loop reading from rfidCom until the number of chars matches the number of chars sent.
You can use a specific terminator of messages and check for it to validate received message
encapsulate chars into a protocol message with an header that embed the message length, so the receiver can count the received chars and stop reading when last char is received.
For example:
void *rfid_to_uart_thread(void *)
{
char rfid_read_buffer[100] = {0};
int writeCounter;
char RXchar;
ssize_t retVal;
bool send = false;
do
{
memset(rfid_read_buffer, 0x00, sizeof(rfid_read_buffer));
send = true;
do
{
retVal = read(rfidCom, &RXchar, 1);
if (retVal > 0)
{
rfid_read_buffer[writeCounter] = RXchar;
writeCounter++;
}
else if (retVal < 0)
{
send = false;
RXchar = '\r'
break;
}
else
{
usleep(25);
}
}
while(RXchar != '\r');
if (send)
{
write(uartCom, rfid_read_buffer, writeCounter);
}
}
while (!bKillBridgeThreads);
return NULL;
}
OK, I've found a solution to my problem I think.
void *rfid_to_uart_thread(void *) {
char rfid_read_buffer[10];
ssize_t writeCounter = -1;
do {
writeCounter = read(rfidCom, &rfid_read_buffer, sizeof(rfid_read_buffer)-1);
if (writeCounter>0){
rfid_read_buffer[writeCounter] = 0;
LOGE("RFID -> UART: %s", rfid_read_buffer);
write(uartCom, rfid_read_buffer, writeCounter);
}else{
usleep(25);
}
tcdrain(uartCom);
} while (!bKillBridgeThreads);
return NULL;}
I've created my own define for a tcdrain, because the Android NDK I am using is not offering it in termios.h
Now, all the values seem to get transmitted to the UART port.
tcdrain is now defined as:
#define tcdrain(fd) ioctl(fd, TCSBRK, 1)

C: sockets: can't read the whole server response

I'm programming in C an IRC chat client. everything it's working well except I can't read the whole answer sent by the server. here's the code:
char buffer[2048];
write_on_screen(current_page(), "LOG COMMAND", command);
write(sockfd, command, strlen(command)); //write to socket
bzero(buffer, sizeof(buffer));
read(sockfd, buffer, sizeof(buffer));
write_on_screen(current_page(), "RESPONSE", buffer);
return buffer;
most of the time buffer will contain just a piece of the response (which is shorter than 2048 bytes) and other times it contains nothing. in both cases if I do another read() after the first one, it returns me the rest of the answer or another small piece (and then I've to do another read() again). if I put a sleep(1) between write() and read() I get the whole answer, but I'm sure this not a good pratice.
Is there some way I can avoid this?
thank you in advance
You're making the usual mistakes. It is impossible to write correct network code without storing the result of read() or recv() into a variable. You have to:
Check it for -1, and if so look at errno to see whether was fatal, which it almost always is except for EAGAIN/EWOULDBLOCK, and if fatal close the socket and abandon the process.
Check it for zero, which means the peer disconnected. Again you must close the socket and abandon the process.
Use it as the count of bytes actually received. These functions are not obliged nor guaranteed to fill the buffer. Their contract in blocking mode is that they block until an error, end of stream, or at least one byte is transferred. If you're expecting more than one byte, you normally have to loop until you get it.
According to RFC-1459, a single line of text in IRC can contain up to 512 characters and is terminated by a CRLF (\r\n) pair. However:
You're not guaranteed to receive exactly 512 bytes each time. For example, you might receive a comparatively short message from someone else one in the channel: Hi!
Related to the above: A group of 512 bytes might represent more than one message. For example, the buffer might contain a whole line, plus part of the next line: PRIVMSG <msgtarget> <message>\r\nPRIVMS
Given that you could have zero-or-more complete lines plus zero-or-one incomplete lines in your buffer[] at any time, you could try doing something along the lines of:
char buffer[2048];
while(keep_going)
{
char **lines;
int i, num_lines;
// Receive data from the internet.
receiveData(buffer);
// Create an array of all COMPLETE lines in the buffer (split on \r\n).
lines = getCompleteLines(buffer, &num_lines);
removeCompleteLinesFromBuffer(buffer);
// Handle each COMPLETE line in the array.
for (i = 0; i < num_lines; ++i) { handle_line(lines[i]); }
freeLines(lines);
}
This would allow you to handle zero or more complete lines in one go, with any incomplete line (i.e anything after the final \r\n pair) being kept around until the next call to receiveData().
You need to loop around read() until a CRLF had been detected.
A possible way to do this would be:
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
ssize_t read_until_crlf(int sd, char * p, size_t s, int break_on_interupt)
{
ssize_t bytes_read = 0;
ssize_t result = 0;
int read_cr = 0;
int read_crlf = 0;
while (bytes_read < s)
{
result = read(sd, p + bytes_read, 1);
if (-1 == result)
{
if ((EAGAIN == errno) || (EWOULDBLOCK == errno))
{
continue;
}
else if (EINTR == errno)
{
if (break_on_interupt)
{
break;
}
continue;
}
else
{
perror("read() failed");
break;
}
}
else if (0 == result)
{
break; /* peer disconnected */
}
if ('\r' == p[bytes_read])
{
read_cr = 1;
}
else if (('\n' == p[bytes_read]) && read_cr)
{
read_crlf = 1;
break; /* CRLF detected */
}
else
{
read_cr = 0;
}
++bytes_read;
}
if (!read_crlf)
{
result = -1; /* Buffer full without having read a CRLF. */
errno = ENOSPC; /* ... or whatever might suite. */
}
return (0 >= result) ?result :bytes_read;
}
Call it like this:
#include <stdio.h>
ssize_t read_until_crlf(int sd, char * p, size_t s, int break_on_interupt);
int main(void)
{
int sd = -1;
/* init sd here */
{
char line[2048] = "";
ssize_t result = read_until_crlf(sd, line, sizeof line, 0);
if (-1 == result)
{
perror("read_until_newline() failed");
}
printf("read '%s'\n", line);
}
return 0;
}

Serial communication not working. Readfile goes wrong

After hours of browsing and reading, I still can't figure out why my code isn't working. I saw similar code snippets on different websites, but I can't seem to get it to work. The writing part is working, but the reading goes wrong. Every 'real character' is followed by three null terminators. Writing a string of 19 characters works and the FPGA I am using gives the correct data on the display. The FPGA should reverse the input and send this pack to the serial port. In the Hyperterminal this is working without any problem.
Can someone maybe point me on my mistake and tell me what I am doing wrong?
Thanks in advance =)
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <time.h>
#include <commdlg.h>
//#include <windef.h>
#define BUFFERLENGTH 19
void writeToSerial(char *line, HANDLE hSerial, DWORD dwBytesWritten);
void printBuffer(char * buffRead, DWORD dwBytesRead);
int main(){
HANDLE hSerial;
COMMTIMEOUTS timeouts;
COMMCONFIG dcbSerialParams;
char *line, *buffWrite, *buffRead;
DWORD dwBytesWritten, dwBytesRead;
/* Create a handle to the serial port */
hSerial = CreateFile("COM3",
GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
NULL);
/* Check if the handle is valid */
if(hSerial == INVALID_HANDLE_VALUE){
if(GetLastError() == ERROR_FILE_NOT_FOUND){
printf("Serial port does not exist \n");
}else{
printf("Port occupied. Please close terminals!\n");
}
}else{
printf("Handle created\n");
/* Check the state of the comm port */
if(!GetCommState(hSerial, &dcbSerialParams.dcb)){
printf("Error getting state \n");
}else{
printf("Port available\n");
/* Configure the settings of the port */
dcbSerialParams.dcb.DCBlength = sizeof(dcbSerialParams.dcb);
/* Basic settings */
dcbSerialParams.dcb.BaudRate = CBR_57600;
dcbSerialParams.dcb.ByteSize = 8;
dcbSerialParams.dcb.StopBits = ONESTOPBIT;
dcbSerialParams.dcb.Parity = NOPARITY;
/* Misc settings */
dcbSerialParams.dcb.fBinary = TRUE;
dcbSerialParams.dcb.fDtrControl = DTR_CONTROL_DISABLE;
dcbSerialParams.dcb.fRtsControl = RTS_CONTROL_DISABLE;
dcbSerialParams.dcb.fOutxCtsFlow = FALSE;
dcbSerialParams.dcb.fOutxDsrFlow = FALSE;
dcbSerialParams.dcb.fDsrSensitivity= FALSE;
dcbSerialParams.dcb.fAbortOnError = TRUE;
/* Apply the settings */
if(!SetCommState(hSerial, &dcbSerialParams.dcb)){
printf("Error setting serial port state \n");
}else{
printf("Settings applied\n");
GetCommTimeouts(hSerial,&timeouts);
//COMMTIMEOUTS timeouts = {0};
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier= 10;
if(!SetCommTimeouts(hSerial, &timeouts)){
printf("Error setting port state \n");
}else{
/* Ready for communication */
line = "Something else\r";
//****************Write Operation*********************//
writeToSerial(line, hSerial, dwBytesWritten);
//***************Read Operation******************//
if(ReadFile(hSerial, buffRead, BUFFERLENGTH, &dwBytesRead, NULL)){
printBuffer(buffRead, dwBytesRead);
}
}
}
}
}
CloseHandle(hSerial);
system("PAUSE");
return 0;
}
void printBuffer(char * buffRead, DWORD dwBytesRead){
int j;
for(j = 0; j < dwBytesRead; j++){
if(buffRead[j] != '\0'){
printf("%d: %c\n", j, buffRead[j]);
}
}
}
void writeToSerial(char *line, HANDLE hSerial, DWORD dwBytesWritten){
WriteFile(hSerial, line, 19, &dwBytesWritten,NULL);
if(dwBytesWritten){
printf("Writing success, you wrote '%s'\n", line);
}else{
printf("Writing went wrong =[\n");
}
}
In this line:
if(ReadFile(hSerial, buffRead, BUFFERLENGTH, &dwBytesRead, NULL))
the buffRead parameter is an uninitialised pointer. Change the declaration to:
char *line, *buffWrite, buffRead [BUFFERLENGTH+1];
Hyper terminal probably doesn't display null characters so it's possible that your fpga is actually sending them.
You could try testing it with Br#y Terminal in hex mode, or looking at the line with an oscilloscope.

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