PHP script to look for a better location of 3G modem

gistfile1.aw

<?php

$fcmd = fopen('/dev/ttyUSB0', 'w');
$fp = fopen('/dev/ttyUSB0', 'r');

if ($fp === false || $fcmd === false) {
    throw new Exception("Failed to open modem device");
}

$levels = array();
echo "Checking";

// switch to 3g only
fwrite($fcmd, "AT^SYSCFG=14,2,3FFFFFFF,2,4\r\n");
fflush($fcmd);
sleep(5);

for ($i = 0; $i < 300; $i++) {
    fwrite($fcmd, "AT+CSQ\r\n");
    fflush($fcmd);

    try {
        $str = '';
        while (!preg_match('/\+CSQ:\s*(\d+),\s*(\d+)/', $str, $matches)) {
            stream_set_blocking($fp, 0);

            $read = array($fp);
            $write = null;
            $except = null;

            if (false === ($num_changed_streams = stream_select($read, $write, $except, null))) {
                throw new Exception("stream_select error");
            } else if ($num_changed_streams == 1) {
                $a = fread($fp, 10);
                $str .= $a;
            } else {
                throw new Exception("stream_select error - $num_changed_streams streams changed, but excepected 1");
            }
        }

        $signal_level = $matches[1];
        #echo "Signal level: $signal_level\n";
        $levels[] = $signal_level;
        echo get_levels_summary($levels) . "\n";
        sleep(1);
    } catch (Exception $e) {
        echo "Error: " . $e->getMessage(); 
    }
}

// switch to 'prefer 3g' mode
fwrite($fcmd, "AT^SYSCFG=2,2,3FFFFFFF,2,4\r\n");
fflush($fcmd);

fclose($fp);

function get_levels_summary($levels) {
    $sum = 0;
    foreach ($levels as $level) {
        $sum += $level;
    }
    $avg = $sum / count($levels);

    $result = "Cnt: " . count($levels) . '; ';
    $result .= "Cur: " . $levels[count($levels) - 1] . '; ';
    $result .= "Max: " . max($levels) . '; ';
    $result .= "Min: " . min($levels) . '; ';
    $result .= "Avg: " . $avg . ";";
    return $result;
}