Waiting for a char received by a serial port (Device::SerialPort)

[Olaf Stetzer]

Hello,

I just did my first steps in programming perl today and got
a "nearly" functioning program. What it should do:
Send a file to /dev/ttyS0 char by char. After each char,
wait for the echo to come back, then continue.
Here is what I wrote, but there seems to be a bug in the
receving/waiting part, it waits endlessly! :-(

Can anyone help me out here?

Thanks,

Olaf

--------------
#!/usr/bin/perl

use Device::SerialPort qw( :PARAM :STAT 0.07);

$Port = "/dev/ttyS0";
$file = "rollei.out";

$device = new Device::SerialPort($Port);
$device->baudrate(9600) || die ("Couldnt set baudrate");
$device->parity("none") || die ("Couldnt Set Parity");
$device->databits(8) || die ("Couldnt Set Databits ");
$device->stopbits(1) || die ("Couldnt set stopbits");
$device->write_settings || die ("No Settings");

open(INFO, $file); # Open for input
@lines = <INFO>; # Read it into an array
close(INFO); # Close the file

foreach $curr_line (@lines) {
for ($i = 0; $i <= length($curr_line); $i++) {
$pass=$device->write(substr($curr_line,$i,1));
$in=1;
while ($in) {
$rcv = $device->input;
if ($rcv ne "") {
print $rcv;
$in=0;
}
}
}
}

undef $device;

[Bbirthisel]

Hi Olaf,

>What it should do:
>Send a file to /dev/ttyS0 char by char.

It looks like it does do that.

> After each char,
>wait for the echo to come back, then continue.

Two issues:

1. What are you doing to get an echo? Are you connecting via a loopback?
The module (and the port itself) does not echo characters back to the
program that writes them.

2. Unless you set them otherwise, linux ports are commonly configured to
receive a full line of data at a time. You can arrange to receive
char-by-char,
see demo6 for a read-timeout-based way, demo8 for a way that samples
from a recurring loop. You can also adjust the port using stty - but that
is
more difficult to get right than using the time-based alternatives.

There is a lot of error handling missing from the script - especially from
critical
operations like "new" and "open" which really can fail. And no "-w" or "use
strict"
either - and BOTH are recommended when working with devices.

I think you should start by running the examples that come with the
distribution,
to see what they do and assure yourself everything is running properly. Then
try
modifying demo8 to do what you want (your file write replaces the section with
the TERM::Readkey call).

Good luck,

-bill