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Question

Good day!

I’m trying to write a program for serial communication on TRB246 from Teltonika (BusyBox v1.34.1).

Incoming data is raw, in hex bytes, coming every seconds.

Three solutions:
1/ Use microcom in a shell script (swift option, should be sufficient)
2/ Write my own program from scratch
3/ Try to customize microcom

1/ Use microcom : a fail
Script:

#!/bin/sh

ask_dataA='xFFx12xB0x80x28x00x01x01x00xEAx00x00x00x00x77xA8x04xFF'


echo "Asking data A..."
echo -en $ask_dataA > /dev/rs485            # send query
nice -20 microcom -t 1100 -s 9600 /dev/rs485 > tmpsf    # listen
if [ -s tmpsf ]; then                   # checks if file is empty
    hexdump -ve '/1 "%02x"' -n 36 tmpsf         # convert to ascii
    echo ""
else
    echo "nothing"
fi

Output:
enter image description here

Sometimes if gives the hex answer as expected.

I am spying the communication using Docklight, every messages travel correctly and on time. It is just the TRB246 that does not catch the answer.

I think I come too late with microcom, since answer comes a few tens of milliseconds after the echo.

2/ Write my own program from scratch: a fail (read() is not working properly)
code:

#include <fcntl.h>
#include <termios.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <errno.h>


#define RS485_DEV       "/dev/ttyS1"
#define RS485_BAUDRATE  B9600
#define RS485_TIMEOUT   0  //in tenths of sec; or use poll() https://man7.org/linux/man-pages/man2/poll.2.html
#define RS485_MINBRD    16 //min bytes to read     see http://manpagesfr.free.fr/man/man3/termios.3.html

#define RS485_IBUFFSIZE 32


int main()
{

  printf("Hello guys!n");
  uint8_t ibuff[RS485_IBUFFSIZE];

  int fd = open(RS485_DEV, O_RDWR | O_NOCTTY | O_NDELAY);

  if (fd == -1) { printf("Failed to open rs485 port: %sn", strerror(errno)); exit(1); }

  struct termios term_conf;
  struct termios new_term_conf;

  if (tcgetattr(fd, &term_conf) == -1)  { printf("Failed to get term config: %sn", strerror(errno)); } //get current settings

  printf("Former terminal configuration:n");
  printf("term_conf:ntc_iflag = %untc_oflag = %untc_cflag = %untc_lflag = %unn",
        term_conf.c_iflag, term_conf.c_oflag, term_conf.c_cflag, term_conf.c_lflag); 
  for (int i=0 ; i<NCCS ; i++)  { printf("tc_cc[%d] = %un", i, term_conf.c_cc[i]); }
  printf("n");
  // Configure terminal settings

  //cfmakeraw(&term_conf);
    // Control flags

    // Input flags
    // convert break to null byte, no CR to NL translation,
    // no NL to CR translation, don't mark parity errors or breaks
    // no input parity check, don't strip high bit off,
    // no XON/XOFF software flow control
  term_conf.c_iflag &= ~(IGNBRK | BRKINT | ICRNL | INLCR | PARMRK | INPCK | ISTRIP | IXON); //cfmakeraw adds IGNCR and removes INPCK

    // Output flags
    // no CR to NL translation, no NL to CR-NL translation,
    // no NL to CR translation, no column 0 CR suppression,
    // no Ctrl-D suppression, no fill characters, no case mapping,
    // no local output processing
  term_conf.c_oflag = 0;

    // Local flags
    // echo off, echo newline off, canonical mode off,
    // extended input processing off, signal chars off
  term_conf.c_lflag &= ~(ECHO | ECHONL | ICANON | IEXTEN | ISIG);

    // Chars processing
  term_conf.c_cflag &= ~(CSIZE | PARENB); //clear current char size mask, no parity checking
  term_conf.c_cflag |= CS8;               //force 8 bit input

    //  Others
  printf("term_conf.c_cc[VTIME] = %d, RS485_TIMEOUT = %d, VTIME = %dnn", term_conf.c_cc[VTIME], RS485_TIMEOUT, VTIME);
  printf("term_conf.c_cc[VMIN] = %d, RS485_MINBRD = %d, VMIN = %dnn", term_conf.c_cc[VMIN], RS485_MINBRD, VMIN);
  term_conf.c_cc[VTIME] = RS485_TIMEOUT;
  printf("term_conf.c_cc[VTIME] = %d, RS485_TIMEOUT = %d, VTIME = %dnn", term_conf.c_cc[VTIME], RS485_TIMEOUT, VTIME);
  term_conf.c_cc[VMIN] = RS485_MINBRD;
  printf("term_conf.c_cc[VMIN] = %d, RS485_MINBRD = %d, VMIN = %dnn", term_conf.c_cc[VMIN], RS485_MINBRD, VMIN);

  if (cfsetispeed(&term_conf, RS485_BAUDRATE) == -1)  { printf("Failed to set term ispeed: %sn", strerror(errno)); }
  if (cfsetospeed(&term_conf, RS485_BAUDRATE) == -1)  { printf("Failed to set term ospeed: %sn", strerror(errno)); }

  tcsetattr(fd, TCSANOW, &term_conf); // apply new conf now 

  tcgetattr(fd, &new_term_conf);      // get conf again
  if (memcmp(&term_conf, &new_term_conf, sizeof(term_conf)) != 0) // compare to check if changes applied
  {
    printf("Terminal configuration failedn");
    printf("term_conf:ntc_iflag = %untc_oflag = %untc_cflag = %untc_lflag = %unn",
        term_conf.c_iflag, term_conf.c_oflag, term_conf.c_cflag, term_conf.c_lflag); 
    for (int i=0 ; i<NCCS ; i++)  { printf("tc_cc[%d] = %un", i, term_conf.c_cc[i]); }
    printf("n");

    printf("new_term_conf:ntc_iflag = %untc_oflag = %untc_cflag = %untc_lflag = %unn",
        new_term_conf.c_iflag, new_term_conf.c_oflag, new_term_conf.c_cflag, new_term_conf.c_lflag); 
    for (int i=0 ; i<NCCS ; i++)  { printf("tc_cc[%d] = %un", i, new_term_conf.c_cc[i]); }
    printf("n");
    printf("new_term_conf.c_cc[VTIME] = %d, RS485_TIMEOUT = %d, VTIME = %dnn", new_term_conf.c_cc[VTIME], RS485_TIMEOUT, VTIME);
    printf("new_term_conf.c_cc[VMIN] = %d, RS485_MINBRD = %d, VMIN = %dnn", new_term_conf.c_cc[VMIN], RS485_MINBRD, VMIN);
  }

  //if (ioctl(fd, TIOCEXCL, NULL) == -1)   { printf("Failed to get exclusivity: %s", strerror(errno)); }

  //if (tcflush(fd, TCIOFLUSH) == -1)   { printf("Failed to flush: %s", strerror(errno)); }

  memset(ibuff, 0, RS485_IBUFFSIZE);
  int i=20000;
  while (i)
  {
    i--;

    if(read(fd, ibuff, 1) !=-1) { printf("%xn", ibuff[0]); }
    usleep(200);
  }

  close(fd);


  //printf("EAGAIN = %dn", EAGAIN);

  return 0;
}

output:

Hello guys!
Former terminal configuration:
term_conf:
    c_iflag = 0
    c_oflag = 0
    c_cflag = 3261
    c_lflag = 0

    c_cc[0] = 3
    c_cc[1] = 28
    c_cc[2] = 127
    c_cc[3] = 21
    c_cc[4] = 16
    c_cc[5] = 0
    c_cc[6] = 0
    c_cc[7] = 0
    c_cc[8] = 17
    c_cc[9] = 19
    c_cc[10] = 26
    c_cc[11] = 0
    c_cc[12] = 18
    c_cc[13] = 15
    c_cc[14] = 23
    c_cc[15] = 22
    c_cc[16] = 4
    c_cc[17] = 0
    c_cc[18] = 0
    c_cc[19] = 0
    c_cc[20] = 0
    c_cc[21] = 0
    c_cc[22] = 0
    c_cc[23] = 0
    c_cc[24] = 64
    c_cc[25] = 235
    c_cc[26] = 119
    c_cc[27] = 0
    c_cc[28] = 0
    c_cc[29] = 0
    c_cc[30] = 0
    c_cc[31] = 100

term_conf.c_cc[VTIME] = 0, RS485_TIMEOUT = 0, VTIME = 5

term_conf.c_cc[VMIN] = 16, RS485_MINBRD = 16, VMIN = 4

term_conf.c_cc[VTIME] = 0, RS485_TIMEOUT = 0, VTIME = 5

term_conf.c_cc[VMIN] = 16, RS485_MINBRD = 16, VMIN = 4

Terminal configuration failed
term_conf:
    c_iflag = 0
    c_oflag = 0
    c_cflag = 3261
    c_lflag = 0

    c_cc[0] = 3
    c_cc[1] = 28
    c_cc[2] = 127
    c_cc[3] = 21
    c_cc[4] = 16
    c_cc[5] = 0
    c_cc[6] = 0
    c_cc[7] = 0
    c_cc[8] = 17
    c_cc[9] = 19
    c_cc[10] = 26
    c_cc[11] = 0
    c_cc[12] = 18
    c_cc[13] = 15
    c_cc[14] = 23
    c_cc[15] = 22
    c_cc[16] = 4
    c_cc[17] = 0
    c_cc[18] = 0
    c_cc[19] = 0
    c_cc[20] = 0
    c_cc[21] = 0
    c_cc[22] = 0
    c_cc[23] = 0
    c_cc[24] = 64
    c_cc[25] = 235
    c_cc[26] = 119
    c_cc[27] = 0
    c_cc[28] = 0
    c_cc[29] = 0
    c_cc[30] = 0
    c_cc[31] = 100

new_term_conf:
    c_iflag = 0
    c_oflag = 0
    c_cflag = 3261
    c_lflag = 0

    c_cc[0] = 3
    c_cc[1] = 28
    c_cc[2] = 127
    c_cc[3] = 21
    c_cc[4] = 16
    c_cc[5] = 0
    c_cc[6] = 0
    c_cc[7] = 0
    c_cc[8] = 17
    c_cc[9] = 19
    c_cc[10] = 26
    c_cc[11] = 0
    c_cc[12] = 18
    c_cc[13] = 15
    c_cc[14] = 23
    c_cc[15] = 22
    c_cc[16] = 4
    c_cc[17] = 0
    c_cc[18] = 0
    c_cc[19] = 0
    c_cc[20] = 0
    c_cc[21] = 0
    c_cc[22] = 0
    c_cc[23] = 161
    c_cc[24] = 7
    c_cc[25] = 64
    c_cc[26] = 0
    c_cc[27] = 168
    c_cc[28] = 152
    c_cc[29] = 232
    c_cc[30] = 119
    c_cc[31] = 104

new_term_conf.c_cc[VTIME] = 0, RS485_TIMEOUT = 0, VTIME = 5

new_term_conf.c_cc[VMIN] = 16, RS485_MINBRD = 16, VMIN = 4

4
fe
4
fe
4
fe
4
fe
4
fe
4
fe

4 and fe are the standard final bytes of my messages. Even if I change the nbytes to read in the function call, I never get the other bytes.
note: over the 10k reads, it returns only a few bytes.
When nothing is returned, read() fails and returns -1, with errno = 11 = EAGAIN, and strerror(errno) gives “Resource temporarily unavailable”.

I have tried to setup VMIN = 0 and VTIME = 12 (1.2 sec), but read() does not wait at all, just as if VTIME = 0. Why?

3/ Try to customize microcom
This is now the solution I am looking for in parallel, trying to make a new program inside busybox, but that’s not proper…

I do thank you very much if you can give an advise on how to make the 1/ script work, or on how to solve the read() issue!

Cheers,

Francis

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