File plugin returns Directory List empty

in my ionic app I just want to list all the files/folders in sd card, im using the cordova-file-plugin

the code is below

.controller('MyCtrl', function($scope, $cordovaFile) {

  document.addEventListener('deviceready', function () {

  var myPath = cordova.file.externalRootDirectory; // We can use the default externalRootDirectory or use a path : file://my/custom/folder

window.resolveLocalFileSystemURL(myPath, function (dirEntry) {
     var directoryReader = dirEntry.createReader();

function onSuccessCallback(entries){
  console.log( 'The magic will happen here, check out entries with');  

function onFailCallback(){
  // In case of error


}); in ngcordova file there is no function i found, so im using cordova javascript code in my ionic app,

The function returns empty array, i hae added the permission also, anyone had similar issue , pls help

and the app does not ask for permission too