Using Serial Port in Linux. Weird problem with receiving data.

[lutherchp]

A baffling end to my week! I open my serial port on my Debian PC (Debian version 5.0.1) I have a decent Null Modem lead going to another PC (I'll call it PC#2), with its port open with the same parameters. I send a series of bytes from the Debian PC which comes through, no problem.

I reply from PC#2, but the read buffer of the Debian PC's port shows nothing. What's more, the message gets sent directly back to the PC#2, with certain bytes getting changed. (I'm guessing its just invalid ascii codes that get changed, e.g. 0x02 always gets changed to 0x5e 0x42, which is ^B. Displayable bytes don't get changed.)

I've tried changing the Flow control method but that hasn't helped.

I'm using php_serial.class.php, from http://www.phpclasses.org/browse/package/3679.html. It is a highly rated class and I'm guessing its not to blame.
My code is a very slight modification of the example that comes with the class (modifying just so it keeps reading any messages for a number of seconds):

include "php_serial.class.php";
$serial = new phpSerial;
 
$serial->deviceSet("COM1");
 
// We can change the baud rate
$serial->confBaudRate(9600);
$serial->confCharacterLength(8);
$serial->confStopBits(1);
$serial->confParity("none");
 
//$serial->confFlowControl ("none");
// Then we need to open it
$serial->deviceOpen();
 
$serial->sendMessage(chr(0xff).chr(0x02).chr(0x4B)); // Sends with no problem
 
do{
    // Or to read from
    $read = $serial->readPort();
    echo $read;
    $pause1 += 0.01;
} while (empty($read) && $pause1 < 99999);
// Read never becomes non-empty whatever I send back from other PC within this time
 
$serial->deviceClose();
 

If anyone has a strong hunch about why I'm getting this problem, or any thing helpful to say, thank you very much.

[lutherchp]

I ought to have included this from the actual class that I downloaded. I now think that this is where the problem is:

        function deviceOpen ($mode = "r+b")
    {
        $this->_dHandle = fopen($this->_device, $mode);
 
        if ($this->_dHandle !== false)
        {
            stream_set_blocking($this->_dHandle, 0);
            $this->_dState = SERIAL_DEVICE_OPENED;
            return true;
        }
 
        $this->_dHandle = null;
        trigger_error("Unable to open the device", E_USER_WARNING);
        return false;
    }
 

I'm pretty sure now that the problem is use of the function stream_set_blocking(). According to user comments on the manual, this function is ignored by php5.2. So it seems the serial port cannot be unblocked - hence data coming in not getting read and getting sent straight back down the line.

Is my only solution to use php4? Anyone know a workaround for the stream_set_blocking() bug?