Hi All,

Currently I have a problem catching (or handling) SIGIOs in a Perl script. What I would like to achieve, is to have a small script reading and writing to a serial port whithout the need to poll it every now and then to see if there is indeed something to read.

The code here under opens a serial port, uses POSIX and Fcntl to configure various parameters (baud rate, etc.) and to put it in asynchronous mode.

A SIGIO handler is set a the beginning of the script, which right now just prints out a string when an IO signal has been caught. sigtrap is there just in case other type of signals are sent (apperently not the case anyway).

Once all that is done ;-) it will write something on the line and wait for the signal(s) - I verified that the device indeed answers ("OK" in this case).

The problem is: no SIGIOs are sent back.. 

use POSIX;
use Fcntl;

use sigtrap qw(die untrapped);


sub SIGIO_Handler {
  my $signame = shift;
  print "Somebody sent me a SIG$signame\n";
}

$SIG{IO} = \&SIGIO_Handler;


$| = 1;
open(LINK, "+</dev/ttyS0") || die "Can't connet to the device: $!";

my $termios = new POSIX::Termios;

$termios->getattr( fileno(LINK) );

my $c_cflag = $termios->getcflag;
my $c_lflag = $termios->getlflag;

$c_cflag |= (CLOCAL | CREAD | CS8);
$c_cflag &= ~(PARENB);
$c_cflag &= ~(CSTOPB);
$c_cflag |=  (CSIZE);

$c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
$c_oflag &= ~(OPOST);

$termios->setcc(VMIN,   0);
$termios->setcc(VTIME, 10);

$termios->setcflag($c_cflag);
$termios->setlflag($c_lflag);
$termios->setoflag($c_oflag);

$termios->setispeed(B2400);
$termios->setospeed(B2400);

$termios->setattr( fileno(LINK), TCSAFLUSH);

# -- Register "myself" ($$) to catch SIGIOs.
fcntl(LINK, &Fcntl::F_SETOWN, $$);
fcntl(LINK, F_SETFL, O_ASYNC);


print LINK "AT\r";

while (1) {
  # -- Just wait and ...
  # -- see if any SIGIO arrives
};

[download]

More precisely, if the script just waits (as it does in the above code) no SIGIOs will be catched. Instead, if (at some point) I start reading what is on the port (meaning: modify the script to actualkly read something at some point).. then the SIGIO_Handler will be used.

So, I dont want the signals to tell me that I am reading on the port.. I want them to tell me that there is something to read in the first place! (before I actually read it "myself").

Can somebody provide any hints/advice?
How can properly catch SIGIOs?
Thanks!

P.S.: by the way, I don't want to use the Device::SerialPort since I have the feeling that it should be possible through POSIX and Fcntl and they are in the standard distribution, or even Win32::SerialPort for the allready given reasons, plus.. Im on Linux (kernel v2.2)

In reply to Handling I/O Signals by stephane

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