Ajax : Call external PHP file

I have event-func.php which I place at the root(/) of my dir installation. This file contains function get-all() {} which returns a json encode string.
I am requesting this from the events-list-manager.php under using this ajax script at the top page.

jQuery.ajax({
			type: "POST",
			url: "event-func.php",
			action: "get-all-a",
			dataType: "jsonp",
			data: {event: "Hi"},
			cache: false,
			success: function(dataa) {
				jQuery("#eventDetails").html(dataa);
			},
			error: function(resultt, statut, error_) {
				jQuery("#eventDetails").html(error_);
			}
		});

This is the content of get-all():

<?php

add_action( 'wp_ajax_nopriv_get-all-a', 'get-all' );

function get-all() {
 echo json_encode("Test OK!");
}
?>

But I am getting an Intenal Error 500 . How can I solve this issue ?