Serial Input for the Pi

Question

I am trying to log slow serial data (about 40 bytes per minute at 9600 baud) on the Pi.

I have a rough program using wiringSerial which only provides unbuffered serialGetchar

I could write a serialGets but wonder if/why it hasn't been done before.

PS The last time I wrote something like this was in the 1980s on CP/M

Answer 1

Do you need to write a program for this or can you just use basic Unix commands? Could you provide us more details on what you want to achieve...

Assuming you serial port is connected through your USB port. You can easily log incoming bytes from serial port by redirecting (or simply listening) the right interface file, such as:

cat /dev/ttySx > /home/myloggin/data.log

In the same way, you can write on the serial port:

echo "command" > /dev/ttySx

To find out on which interface file your device is available, check /var/log/dmesg or issue a lsusb.

Answer 2

I want the equivalent of fgets(), and was going to write this using serialGetchar but the timeout caused problems, requiring post processing.

I realised the required functionality was already in the kernel, it just required different initialisation.

#include <stdio.h>
#include <termios.h>
#include <unistd.h>

#include <wiringPi.h>
#include <wiringSerial.h>

/*
 * serialOpenB:
 *  Open and initialise the serial port, 
 *  setting canonical mode, ignore CR on input, no timeout
 *********************************************************************************
 */
int serialOpenB (const char *device, const int baud, const int max)
{
    struct termios options ;
    int fd = serialOpen(device, baud);
    // Get and modify current options:
    tcgetattr (fd, &options) ;

    options.c_lflag |= ICANON;  // set canonical mode (line by line)
    options.c_iflag |= IGNCR;   // ignore CR on input
    options.c_cc [VMIN] = max-1;    // return if max-1 bytes received
    options.c_cc [VTIME] = 0;   // no timeout

    tcsetattr (fd, TCSANOW | TCSAFLUSH, &options) ;

    usleep (10000) ;    // 10mS

    return fd ;
}


/* Get a newline-terminated string of finite length.
 *********************************************************************************
 */

char * serialGets (char *buf, const int n, const int fd)
{
    int m;
    m = read (fd, buf, n);
    *(buf+m) = '\0';
    return (buf) ;
}