android widget update period milles not working

I am a new android developer trying to code a widget.. The "updatePeriodMillis" parameter tell the widget to call onupdate method after the given duraion but it doesn't happen so for me....

can some one please point my mistake.. here are my files

src/hellowidget.java

package de.thesmile.android.widget;

import android.appwidget.AppWidgetProvider;
import java.util.Random;

import android.appwidget.AppWidgetManager;
import android.content.Context;
import android.content.Intent;
import android.widget.RemoteViews;



public class HelloWidget extends AppWidgetProvider {
    int number =0;


    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager,
            int[] appWidgetIds) {

         number = (new Random().nextInt(100));
        for (int appWidgetId : appWidgetIds) {


            RemoteViews views = new RemoteViews(context.getPackageName(),R.layout.main);
            views.setTextViewText(R.id.TextView01, String.valueOf(number));
            appWidgetManager.updateAppWidget(appWidgetId, views);

        }

    }


}

xml/hello_widget_provider.xml

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
android:minWidth="146dip"
android:minHeight="72dip"
android:updatePeriodMillis="1000"
android:initialLayout="@layout/main"
/>

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="fill_parent"
android:orientation="vertical"

android:layout_gravity="center"
android:layout_height="wrap_content">
<TextView android:text="@+id/TextView01" android:id="@+id/TextView01" android:layout_width="wrap_content" android:layout_height="wrap_content"></TextView><TextView android:padding="10dip" android:layout_marginTop="5dip" android:layout_gravity="center_horizontal|center" android:text="@string/widget_text" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/widget_textview" android:textColor="@android:color/black"></TextView>


</LinearLayout>

android manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="de.thesmile.android.widget"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<!-- Broadcast Receiver that will process AppWidget updates -->
<receiver android:name=".HelloWidget" android:label="@string/app_name">
<intent-filter>
<action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
</intent-filter>
<meta-data android:name="android.appwidget.provider"
android:resource="@xml/hello_widget_provider" />
</receiver>
</application>
<uses-sdk android:minSdkVersion="7" />
</manifest>