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Writing to a Serial Port

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# 43  
Old 10-28-2014
Corona688 -

Thanks.

I changed the permissions to 666.

Same behavior. When I execute the program, it hangs, no error message.

---------- Post updated at 02:00 PM ---------- Previous update was at 01:57 PM ----------

If it helps at all, we had a power failure at this end, but I was able to restart everything. Maybe I missed something
# 44  
Old 10-28-2014
I added a program to my message.
# 45  
Old 10-29-2014
Corona688

Thanks.

Checked w/ minicom. Works beautifully.

Tried w/ your code. Compiles, links. Hangs on command line and in the PHP code.
# 46  
Old 10-29-2014
If it doesn't work from prompt it's certainly not going to work from php, it's not magic.

The incredibly frustrating thing about this is we have absolutely no way to test anything we do. Everything we say is a shot in the dark. For all we know minicom is doing translation.

Try stty -g -F /dev/ttyS0 while minicom is running.

Try this code.

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

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

int main() {
        char buf[64];
        int pos=0;

        int fd;
        fprintf(stderr, "About to open /dev/ttyS0\n");
        fd=open("/dev/ttyS0", O_RDWR);
        if (fd < 0) {
            perror("Couldn't open");
            exit(1);
        }

        fprintf(stderr, "Wrote %ld bytes\n", (long int)write(fd, "W\r\n", 3));

        tcdrain(fd);

        while(read(fd, buf+pos, 1) == 1)
        {
                fprintf(stderr, "Read 0x%02x\n", buf[pos]);
                if(buf[pos++] == '\n') break;
        }

        buf[pos]='\0';

        printf("got line:\n%s", buf);
}

Tell me everything it outputs.

Make sure nothing else is holding /dev/ttyS0 again.
Last edited by Corona688; 10-29-2014 at 12:22 PM..
# 47  
Old 10-29-2014
Corona688 -

Thanks.

I'll try your suggestions when I get home, approx 8pm EDT.

What is absolutely confusing to me is that I had a C program and a PHP script that ran perfectly from both the command line and a as a script, then suddenly stopped running.
# 48  
Old 10-29-2014
Quote:
Originally Posted by Meow613
What is absolutely confusing to me is that I had a C program and a PHP script that ran perfectly from both the command line and a as a script, then suddenly stopped running.
I bet the terminal settings on /dev/ttyS0 changed. They are global... If you change it, it stays changed until something else changes it (or the computer reboots). Terminal settings can do a lot, not just baud rate but things like "should I force you to wait until there's an entire line?", "how many seconds until I give up, or wait forever?" and "should I strip out or translate carriage returns, or give them to you raw?"

That's probably why it works in minicom and not your shell, too. minicom knows how to set up the terminal. And why I want the printout from stty -g -F /dev/ttyS0 while minicom is running -- if we can get its "working" settings maybe we can steal them.
# 49  
Old 10-30-2014
Corona688 -

Thanks

Excellent.

I'll try it when I get home.

I'll also try minicom to set the parameters, since we had power failure.

UPS!!!

---------- Post updated at 08:16 PM ---------- Previous update was at 01:10 PM ----------

Corona688 -

Thanks.



Code:
root@meow:/var/www#  stty -g -F /dev/ttyS0 
1:0:80000dad:0:3:1c:7f:15:4:5:1:0:11:13:1a:0:12:f:17:16:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0

Tell me everything it outputs.

Make sure nothing else is holding /dev/ttyS0 again.
Code:
About to open /dev/ttyS0
Wrote 3 bytes

---------- Post updated 10-30-14 at 10:08 AM ---------- Previous update was 10-29-14 at 08:16 PM ----------

Corona688 -

Thanks.

A new listing of stty -


Code:
root@meow:/var/www#  stty -a -F /dev/ttyS0
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 hupcl -cstopb cread clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff
-iuclc -ixany -imaxbel -iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt
echoctl echoke

Sorry. The above was run while minicom was NOT running. Here it is when minicom IS running. Note the differences.

Code:
root@meow:/var/www#  stty -a -F /dev/ttyS0
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 5;
parenb -parodd cs7 hupcl -cstopb cread clocal crtscts
ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany -imaxbel -iutf8
-opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
-isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase -tostop -echoprt -echoctl -echoke

Last edited by Meow613; 10-30-2014 at 11:58 AM..
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