// /app/config/config.yml

framework:
    charset:       UTF-8
    error_handler: null
    csrf_protection:
        enabled: true
        secret: xxxxxxxxxx
    router:        { resource: "%kernel.root_dir%/config/routing.yml" }
    validation:    { enabled: true, annotations: true }
    templating:    { engines: ['twig'] } #assets_version: SomeVersionScheme
    session:
        default_locale: en
        lifetime:       3600
        auto_start:     true
        name:           diem

# Twig Configuration
twig:
    debug:            %kernel.debug%
    strict_variables: %kernel.debug%

# Assetic Configuration
assetic: ~

## Doctrine Configuration
doctrine:
   dbal:
       dbname:   sf2_diem
       user:     root
       password: salut
       logging:  %kernel.debug%
   orm:
       auto_generate_proxy_classes: %kernel.debug%
       mappings:
           diemBundle: ~
       proxy_namespace: Proxies
       proxy_dir: %kernel.cache_dir%/doctrine/orm/Proxies
       default_entity_manager: default
       default_connection: default
       metadata_cache_driver: apc
       query_cache_driver: apc
       result_cache_driver: apc
       entity_managers:
           default:
               connection:       default



// /src/diem/diemBundle/Entity/User.php
<?php
namespace diem\diemBundle\Entity;

/**
 * @orm:Entity
 */
class User
{
    /**
     * @orm:Id
     * @orm:Column(type="integer")
     * @orm:GeneratedValue(strategy="IDENTITY")
     */
    protected $id;

    /**
     * @orm:Column(type="string", length="255")
     */
    protected $name;
}

Then running php app/console doctrine:generate:entities diemBundle gives me:
[RuntimeException]
  Bundle diemBundle does not contain any mapped entities.