Parsing large xml inside CDATA using PHP XMLReader

I have to parse 1.5 Giga XML file using XMLReader for php. This files are structured in block of data. Inside each block of data I have a CDATA part that contains huge xml code that I have to parse too.

Using XMLReader I can access to the file and read it in streaming. How can I read the embedded CDATA xml and parse it without have error of "huge input lookup".

What I do:

    case (XMLREADER::CDATA):
                        // echo  "found CDATA \n" ;
                        $value = $reader->value;    echo "Read CDATA\n";
                        $xmlReader = new XMLReader(); echo "New XMLReader\n";
                        $xmlReader->xml ( $value) ; echo "Parsing CDATA ... \n";
                        $nTx =0;
                        $_root ="";
                        $_parent= array();
                        $_name = "NONE";
                        $_liv=0;

                        echo "Start ... \n";

                        while ( $xmlReader->read()) {
...

This fails when I do $value = $reader->value; because too large data. How can read in streaming the CDATA block ? Thnx