Как отменить метод $ interval без ng-click?

angular.module('demoApp', [])
	.controller('TimerController', TimerController)
	.controller('StopController', StopController);

function TimerController($scope, $interval) {
    var self = this,
        intPromise;
    
    $scope.$on('timerEvent:stopped', function() {
    	intPromise = null; // timer stopped in other controller
    });
    
	this.start = function() {
        if (!intPromise) {
    		intPromise = $interval(update, 1000);
        	$scope.$emit('timerEvent:start', intPromise);
        }
    }
    
    function update() {
    	self.value = Math.round(Math.random()*100, 0);
    }     
}

function StopController($rootScope, $interval) {
	var self = this;
    
    $rootScope.$on('timerEvent:start', function(evt, promise) {
        console.log(promise);
    	self.timerPromise = promise;
    });
    
    this.stop = function() {
        console.log('stoppin', self.timerPromise);
        if ( self.timerPromise ) {
    		$interval.cancel(self.timerPromise);
            $rootScope.$broadcast('timerEvent:stopped');
        }
    };
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="demoApp">
    <div ng-controller="TimerController as timerCtrl">
        <button ng-click="timerCtrl.start()">start</button>
        {{timerCtrl.value}}
    </div>
    
    <div ng-controller="StopController as stopCtrl">
        <button ng-click="stopCtrl.stop()">stop</button>
    </div>