Reading arduino serial in linux using C

Question

I want to read serial from arduino. I use this 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/ioctl.h>
int main(){
    char data[1024];
    char dev[] = "/dev/ttyACM1";
    int fd = open(dev, O_RDWR | O_NOCTTY | O_NDELAY);
    fcntl(fd, F_SETFL, FNDELAY);
    struct termios options;
    tcgetattr(fd, &options);
    cfsetispeed(&options, B9600);
    cfsetospeed(&options, B9600);
    options.c_cflag |= CS8;
    options.c_cflag |= CS8;
    options.c_cflag &= ~CRTSCTS;
    options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    tcsetattr(fd, TCSANOW, &options);
    ioctl(fd, TCFLSH, 2);
    while(1){
        read(fd, data, sizeof(data));
        printf(data);
    }
    //write(fd, data, sizeof(data));
}

My arduino runs very simple sketch :

int x; 
void setup() {
  Serial.begin(9600);
}
void loop() {
  Serial.println("DO YOU HEAR ME ??");
  delay(1000);
}

and output of this combinatin is that :

??OU HEAR ME ??
DO YOU HEAR ME ??
DO YOU HEAR ME ??
A¹þ
??OU HEAR ME ??
DO YOU HEAR ME ??
DO YOU HEAR ME ??
A¹þ
??OU HEAR ME ??
DO YOU HEAR ME ??
DO YOU HEAR ME ??

My question is how to make order out of chaos. I found that this issue occurs when buffer ends and new one begins(bigger buffer less junk data) but I can't have a infinite buffer. Also there is a lot of junk when it reads for the first time.. Is there a way to sync it or something ?

(Also I am not native English sorry for any mistakes.)

@DavidCullen I enabled cannonical input and now the junk only happens at the beginning of the line.. so I am now assuming that is has some extra bits on input.. But I don't know from where (it is like 3 chars, 3bytes). — Kozlowsqi
– Kozlowsqi, Commented Apr 16, 2017 at 20:49
one side note, try to increase the baud rate and see does it solves the problem? — danglingpointer
– danglingpointer, Commented Apr 16, 2017 at 21:16
@LethalProgrammer Nope I tried... I think it Has to do something with flags but I don't know with is with at this point... Why it can't be like sending ? Just write and read ? — Kozlowsqi
– Kozlowsqi, Commented Apr 16, 2017 at 21:25
If you don't check the return value of read, it might return with an error value. However, your program will still print the data buffer. Also, on success, the return value of read will be the number of bytes read, which you should use to make sure that data is null terminated. — user3657941
– user3657941, Commented Apr 17, 2017 at 15:50

RamblingMad · Accepted Answer · 2019-12-28 10:57:09Z

I found answer to my own problem. I used this time c++ to organize it in class (very poor one because it doesn't handle any errors and doesn't use c++ in the most..) Here is the code :

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <strings.h>

#include <cstring>
#include <iostream>
//Here I define some vars 
#define BAUDRATE B9600
#define MODEMDEVICE "/dev/ttyACM0"
#define _POSIX_SOURCE 1

class serial{
public:
serial(){
    fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
    if (fd <0) {perror(MODEMDEVICE); exit(-1); } 
    // Improvement No. 1 I save old setting and clean the new one 
    tcgetattr(fd,&oldtio);
    bzero(&newtio, sizeof(newtio));

    // Here I set all the flags to vars at once
    newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
    newtio.c_iflag = IGNPAR | ICRNL;
    newtio.c_oflag = 0;
    newtio.c_lflag = ICANON;
    //here I set some new flags..
    newtio.c_cc[VINTR]    = 0;     /* Ctrl-c */
    newtio.c_cc[VQUIT]    = 0;     /* Ctrl-\ */
    newtio.c_cc[VERASE]   = 0;     /* del */
    newtio.c_cc[VKILL]    = 0;     /* @ */
    newtio.c_cc[VEOF]     = 4;     /* Ctrl-d */
    newtio.c_cc[VTIME]    = 0;     /* inter-character timer unused */
    newtio.c_cc[VMIN]     = 1;     /* blocking read until 1 character  arrives */
    newtio.c_cc[VSWTC]    = 0;     /* '\0' */
    newtio.c_cc[VSTART]   = 0;     /* Ctrl-q */
    newtio.c_cc[VSTOP]    = 0;     /* Ctrl-s */
    newtio.c_cc[VSUSP]    = 0;     /* Ctrl-z */
    newtio.c_cc[VEOL]     = 0;     /* '\0' */
    newtio.c_cc[VREPRINT] = 0;     /* Ctrl-r */
    newtio.c_cc[VDISCARD] = 0;     /* Ctrl-u */
    newtio.c_cc[VWERASE]  = 0;     /* Ctrl-w */
    newtio.c_cc[VLNEXT]   = 0;     /* Ctrl-v */
    newtio.c_cc[VEOL2]    = 0;     /* '\0' */
    // and I finally save the settings 
    tcflush(fd, TCIFLUSH);
    tcsetattr(fd,TCSANOW,&newtio);
}
~serial(){
    close(fd);
}

    std::string sread(){
        res = read(fd,buf,255);
        buf[res]=0;
        return buf;
    }
    void swrite(const char* input){
        write(fd,input,std::strlen(input));
    }
private:
    int fd,c,res;
    struct termios oldtio,newtio;
    char buf[255];
};


int main(){
    serial s;
    s.swrite("Light");
    std::string buf = s.sread();
    std::cout << buf;
}

This is more of a ripoff from "Serial programming HOW TO" : http://tldp.org/HOWTO/Serial-Programming-HOWTO/ (form the example code..)

And here is the new poor arduino code :

int x; 
String buff;
int lpin = A0;
int tpin = A1;
int data;
void setup() {
  Serial.begin(9600);
  pinMode(lpin,INPUT);
  pinMode(tpin,INPUT);
}
void loop() {
  if(Serial.available() == 1)
  {
    buff = Serial.readString();
    if(buff == "Light"){
      data = analogRead(lpin);
      Serial.print(data);
      Serial.print("\n");
    }else if(buff == "Temp"){
      data = analogRead(tpin);
      Serial.print(data);
      Serial.print("\n");
    }else{
      Serial.print("Something went wrong !");
      Serial.print("\n");
    }
  }
  delay(1);
}

Collectives™ on Stack Overflow

Reading arduino serial in linux using C

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related