volatile changes

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

controllers.blog.js

import Ember from 'ember';
const { Controller, inject, computed, observer } = Ember;

export default Controller.extend({
  post: inject.controller('blog/post'),
  
  selectedPostTitleDidChange: observer('post.model.cp', function() {
    console.log('a');
  })
});

controllers.blog.post.js

import Ember from 'ember';
const { Controller, Object: EmObject, computed } = Ember;

const PostModel = EmObject.extend({
  cp: computed('title', {
    get() {
      return this.get('title').toUpperCase();
    },
    set(k, v) {
      this.set('title', v.toLowerCase());
      return v.toUpperCase();
    }
  }).volatile()
});

export default Controller.extend({
  model: PostModel.create({
    title: 'A blog Post'
  }),
  actions: {
    changeTitle() {
      this.set('model.cp', 'A New Title');
    }
  }
});

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('blog', function() {
    this.route('post');
  });
});

export default Router;

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{#link-to "blog.post"}}Go to post route{{/link-to}}
<br>
{{outlet}}
<br>
<br>

templates.blog.hbs

<h3>Blog</h3>

Selected post: {{post.model.cp}}

{{outlet}}

templates.blog.post.hbs

<h4>{{model.title}}</h4>
<button onclick={{action "changeTitle"}}>Change title</button>

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.1.2",
    "ember-data": "2.0.1",
    "ember-template-compiler": "2.1.2",
    "ember-testing": "2.1.2"
  },
  "addons": {}
}