php read data from serial port on linux

Question

I try to read serial port on Linux platform using PHP.
But I cant read any data. When I try to read using .net, this time I can read.

I use "php_serial.class.php" class for serial port operations. You can read this class from this link :
here

My code is like this :

<?php  
 include "php_serial.class.php";  

// Let's start the class
$serial = new phpSerial;

// First we must specify the device. This works on both linux and windows (if
// your linux serial device is /dev/ttyS0 for COM1, etc)
$serial->deviceSet("/dev/ttyS1");

// We can change the baud rate, parity, length, stop bits, flow control
$serial->confBaudRate(19200);
$serial->confParity("none");
$serial->confCharacterLength(8);
$serial->confStopBits(1);
$serial->confFlowControl("none");

// Then we need to open it
$serial->deviceOpen();  

// read from serial port
$read = $serial->readPort();

//Determine if a variable is set and is not NULL
if(isset($read)){
   while(1){
       $read = $serial->readPort();
       print_r(" (size ".strlen($read). " ) ");
       for($i = 0; $i < strlen($read); $i++)
       {
          echo ord($read[$i])." ";
       }
       print_r("\n");
       sleep(1);
  }// end while
}// end if  


// If you want to change the configuration, the device must be closed
$serial->deviceClose();

// We can change the baud rate
$serial->confBaudRate(19200);  
?>

the line "print_r(" (size ".strlen($read). " ) ");" always return zero. What is the reason why I cant read data from serial port?

DId you try to run "cat /dev/ttyS1" for example as the PHP user (probably named Apache or www-data)? Does this user have read-access to /dev/ttyS1 ? — Erwin Moller
yes, user has read-access to /dev/ttyS1. I am using com2 port and I can open port and send data to port. But I cant read data from port. Also I try "cat /dev/ttyS1" but cant read anything as well. — cukcuk
Have you checked that your PHP install is configured to report errors and warnings? The class uses warnings to report issues. Try adding trigger_error("logging is working", E_USER_WARNING); at the top of the script - if you don't see it in the output, then it's likely something is failing later and you're suppressing the error message. — symcbean
I have already use trigger_error in php_serial class to check any error or warning. My problem is not about it. My problem is to read data from serial port on linux. I use $read = $serial->readPort(); for reading but sometimes it can read , sometimes it cant — cukcuk

mrmin24 mrmin24 · Accepted Answer · 2012-10-04T08:46:44

I am sure you have rsolved this by now, but here is my 2c worth.

You read the serial port twice. Once to check if there is data and then again when there is data. In my experience, reading it once clears the buffer and thus reading it again will yield an empty result.

Just do not read it the second time

php read data from serial port on linux

3 Answers