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Top Forums Programming Wrong data with Read from a serial port. Post 302731423 by enaud on Thursday 15th of November 2012 03:01:17 AM
Old 11-15-2012
Quote:
Originally Posted by achenle
Also, the read() library call returns "ssize_t", not "long int". They might coincidentally be the same on your system's architecture, but they are not the same by definition. You then truncate the "long int" value by returning an "int" from your readPort() method.

Also, you are not checking the return values for your calls to fcntl(), tcgetattr(), cfsetispeed(), cfsetospeed(), or tcsetattr(). How do you know if those calls succeeded?
how checking the return values for my calls? thanks?

I've modified my Read Function:

Code:
int cClassSerialLIB::ReadPort_poll(){
 
    int iIn;
    struct pollfd pfds[5];
 
    pfds[0].fd     = fd;
    pfds[0].events = POLLIN;
    int nfds = 1;
 
    while(1){
        /* poll aspetta indefinitivamente (-1) */
        int pollret = poll(pfds, nfds, -1);
 
        if (pollret == -1) {
           //perror("poll");
           continue;
        }
 
        /* 2) timeout: this should never happen really... */
        if (pollret == 0) {
 
           continue;
        }
 
        if(pfds[0].revents == POLLIN){
               iIn = read(fd, array_uart2, sizeof(array_uart2));
               if (iIn < 0)
               {
                   if (errno == EAGAIN)
                   {
                           continue; // assume that command generated no response
                   }
                   else
                   {
                           printf("read error %d %s\n", errno, strerror(errno));
                   } // end if
               }
 
               aggiorna1();
        }
    }
}

aggiorna() is decodified function of my packets data, infact i receive a packet data(310 byte at max) every 50ms and so (115200 8n1) i have 1byte every 87us and so 27 ms for trasmission!

With this function i have error in my arrayuart2(the work's buffer) infact i have error on byte for example len payload is wrongor other similar errors:

My protocol:

M A M <-- header first 3 bytes
len payload <-- 2 byte
payload <--1--300 byte
EOM='m' <--1 byte
checksum<--1 byte


If i write
if(pfds[0].revents == POLLIN){
sleep(1);
iIn = read(fd, array_uart2, sizeof(array_uart2));

It work without errors but i think that i lose some packets of data because i receive data every 50ms and i wait 1second...

Thanks
Regards

Last edited by enaud; 11-15-2012 at 04:55 AM..
 

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explain_poll_or_die(3)					     Library Functions Manual					    explain_poll_or_die(3)

NAME
explain_poll_or_die - wait for some event on file descriptor and report errors SYNOPSIS
#include <libexplain/poll.h> int explain_poll_or_die(struct pollfd *fds, int nfds, int timeout); int explain_poll_on_error(struct pollfd *fds, int nfds, int timeout); DESCRIPTION
The explain_poll_or_die function is used to call the poll(2) system call. On failure an explanation will be printed to stderr, obtained from the explain_poll(3) function, and then the process terminates by calling exit(EXIT_FAILURE). The explain_poll_on_error function is used to call the poll(2) system call. On failure an explanation will be printed to stderr, obtained from the explain_poll(3) function, but still returns to the caller. fds The fds, exactly as to be passed to the poll(2) system call. nfds The nfds, exactly as to be passed to the poll(2) system call. timeout The timeout, exactly as to be passed to the poll(2) system call. RETURN VALUE
The explain_poll_or_die function only returns on success, see poll(2) for more information. On failure, prints an explanation and exits, it does not return. The explain_poll_on_error function always returns the value return by the wrapped poll(2) system call. EXAMPLE
The explain_poll_or_die function is intended to be used in a fashion similar to the following example: int result = explain_poll_or_die(fds, nfds, timeout); SEE ALSO
poll(2) wait for some event on a file descriptor explain_poll(3) explain poll(2) errors exit(2) terminate the calling process COPYRIGHT
libexplain version 0.52 Copyright (C) 2010 Peter Miller explain_poll_or_die(3)
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