Note: Descriptions are shown in the official language in which they were submitted.
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SOFTWARE ARCHITECTURE FOR A TELEVISION SET-TOP TERMINAL PROVIDING
COMPATIBILTTY WITH
MULTIPLE OPERATING ENVIRONMENTS
BACKGROUND OF THE INVENTION
This application claims the benefit of U.S.
Provisional Application No. 60/135,221, filed May 21,
1999.
The present invention provides a software
architecture that enables core software of a television
set-top terminal to be compatible with different
operating environments.
The recent advent of digital set-top terminals has
spurred the growth of subscriber television networks,
such as cable/satellite television networks. Such
terminals can support increased levels of programming
services and a variety of software-based applications
and functions, such as an electronic program guide,
stock or weather banners, shop and bank at home
services, games, and the like. Moreover, this trend is
expected to continue with the convergence of telephone,
television and computer networks, and the rise of in-
home computer networks.
A digital set-top box (e. g., subscriber terminal)
for cable or satellite television, or the like, requires
OS software, middleware and device drivers to function.
OS software provides the multithreading, real-time
OS support needed to operate the set-top.
Middleware is software that connects two otherwise
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separate applications. For example, such middleware can
be provided to mediate between an application program
and a network, thereby managing the interaction between
disparate applications across heterogeneous computing
platforms. More generally, middleware serves as the
glue between separate applications, and is sometimes
referred to as "plumbing" because it connects two sides
of an application and passes data between them.
Moreover, drivers are used to control different
hardware devices in a terminal, such as tuners,
demodulators, MPEG-2 decoders (e.g., audio, video, and
data), video encoders, audio mixers, and so forth.
In a set-top box, "core software" is provided that
allows the set-top to provide such necessary television
functions as service acquisition, system information
(SI) management, download capability (e.g., for new
application and OS software), return path communication
(e. g., for polling the set-top for billing purposes),
set-top configuration, and conditional access control
(i.e., security).
In the past, each set-top has only been designed to
use one particular operating environment. The problem
of handling multiple operating environments has not
previously been addressed in the set-top environment.
Generally, applications have been ported to various
operating environments either through rewrite of the
set-top system software to that environment or through
an abstraction layer.
Accordingly, it would be advantageous to enable a
choice of different operating environments on a set-top
without the need to change the core set-top system
software. This would enable the reuse of a single set-
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top design for multiple operating environments. It
would also enable faster implementation of alternate
operating software environments, permitting a faster
time to market new set-top devices.
In particular, it would be desirable to have a
software architecture that allows a customer, such as a
cable television system operator, to choose the
operating environment, including the OS kernel,
middleware and application software, and device drivers,
that will be used in the set-top. The core set-top
system software should allow the device to operate
within a common system environment. The architecture
should allow for the development of the core software,
and then implementation of the architecture in any of a
plurality of different operating environments, such as
VRTX, Windows CE, AperiOS, PowerTV and other set-top
operating environments.
The architecture should be suitable for terminals
that receive programming services via any type of
network, including broadband communications networks,
Digital Subscriber Loop (DSL) networks, and others.
The present invention provides a software
architecture that enjoys the aforementioned and other
advantages.
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SUMMARY OF THE INVENTION
In accordance with the present invention, a
software architecture is provided to enable core
software of a set-top device to operate in any of a
plurality of different operating environments.
In a particular embodiment, an apparatus for
providing a software architecture for implementing a
television subscriber terminal includes a computer
readable medium having computer program code means, and
means for executing the computer program code means to
implement a layered software architecture. The
architecture includes: a first, hardware layer, a
second, device driver layer, a third, device driver
interface layer, a fourth layer with the core system
software for providing television functions, and a
kernel abstraction function, a fifth layer for
middleware porting, and a sixth layer providing
middleware to interface with at least one application
program (at a seventh layer).
The kernel abstraction layer and the device driver
interface layer enable the core system software to
operate in different operating environments.
Moreover, an operating system (OS) kernel is provided at
the fourth and fifth layers.
The architecture further includes a software
interface between the core system software and the fifth
layer that enables the core system software to operate
in the different operating environments.
The television functions of the core system
software include one or more of: message reception and
distribution, system information processing, terminal
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configuration, terminal control message processing,
service acquisition, conditional access control,
download capability, return path communication, and
diagnostic data management.
5 Moreover, the television functions may include
conditional access services, including one or more of:
object authentication, object authorization, resource
authorization, baseline privacy key exchange services,
and cryptographic functions.
A corresponding method is also presented.
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BRIEF DESCRIPTION OF THE DRAWING
The Figure depicts a television subscriber terminal
architecture in accordance with the invention.
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DETAILED DESCRIPTION OF THE INVENTION
The Figure illustrates a software platform, or
achitecture, for implementing a set-top box in
accordance with the present invention. The platform can
be implemented using any suitable operating system, such
as the VRTX (virtual real-time executive) operating
system available from Mentor Graphics Corporation of
Wilsonville, Oregon, Windows CE available from Microsoft
Corporation of Redmond, Washington, AperiOS available
from Sony Corporation of New York, N.Y., PowerTV
available from PowerTV, Inc. of Cupertino, CA, etc.
The architecture can be considered to include three
main levels, including a lower level (functions 30, 32
and 34) related to hardware and device driver functions,
a middle level (functions 14, 16, 18, 20, 22, 24 and 26)
related to the core set-top software, and a high level
(functions 10, 12) related to middleware and
applications.
Specifically, the top level of the software
structure comprises one or more application programs 10
which can comprise, for example, the Digital Television
(DTV) navigator application (available from Liberate
Technologies of San Carlos, California), interactive
games, enhanced television features, Internet web
browsers, etc. These applications need to communicate
with the core set-top system software 20. This
communication is accomplished with the
middleware/application interface 12, the middleware
porting layer 14, and the software interface 26.
The next layer in the software structure comprises
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middleware/application interface APIs (application
program interfaces) 12. This layer 12 is part of the
operating environment (i.e., it is OS-specific), and
provides the interface to the application programs) 10
which execute in the set-top (e.g., cable set-top
hardware 34). The layer 12 provides facilities for
applications to use and control the set-top box
resources, and to coexist with other applications. The
layer 12 also provides the environment in which the
applications execute. Layer 12 also provides the API to
which applications are written, providing an authoring
environment. Moreover, this layer 12 handles the issues
of shared resources, multiple applications, application
selection, application launch and application
termination. Preferably, it provides a consistent
interface to the end user.
A middleware porting layer 14, e.g., for cable, DSL
or other television services, is provided to translate
the television, graphics and communication interfaces
20, 22 and 24, respectively, to the particular
functional interface required by a middleware software
component and specified by the middleware
provider/vendor. Middleware providers often specify an
interface on which their software has been tested and
proven. This layer 14, which is also part of the
operating environment, allows portability of the
middleware solution to the set-top in an expedient
manner. More specifically, the layer 14 allows the
core set-top system software 20 to remain the same while
allowing different middleware layers to execute.
An operating system (OS) kernel 16 is provided at
the levels of the middleware porting layer 14 and the
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core set-top system software 20, the graphics, audio,
video subsystem 22 and the network communication stacks
24. This kernel 16 can comprise, for example, a MIPS
(million instructions per second) port of the VRTX
kernel version 4.0, available from the Microtec division
of Mentor Graphics Corporation for the Motorola 68000
family of microprocessors. This kernel 16 provides the
multithreading, real time OS support needed to operate
the set-top. The OS kernel 16, together with the
middleware porting layer 14 and middleware/application
interface APIs 12, and the device drivers are components
of the operating environment. More particularly, the OS
kernel 16 provides OS facilities such as multitasking,
inter-task communication, synchronization, and memory
management. These facilities are used to create tasks,
set task priorities, communicate between tasks, and
synchronize operation of the system tasks and
application tasks.
A kernel abstraction component 18 in accordance
with the present invention provides generic kernel
functions needed by the other components. In
particular, component 18 abstracts these functions from
the specifics of the OS kernel 16. The kernel
abstraction component 18 includes two sections, namely,
(i) the kernel calls used by the components, and (ii)
the kernel-specific translations. Some of the supported
kernel features are implemented in a fashion that is
independent of the underlying kernel.
In accordance with the present invention, the
kernel abstraction component 18 separates the details of
the OS kernel from the core set-top system software 20,
and is used to isolate the core system software from the
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specifics of an OS kernel implementation. In this
manner, portability of the core software 20 between
operating environments is provided. The OS kernel
abstraction 18 provides standard types of OS services in
5 a generic way to the core system software 20. These
services include, e.g., messaging, thread operations,
memory management, synchronization, and event
management.
The core set-top system software 2Q contains
10 support for the television system features. For
example, this software can be written to support the
DigiCipher~ II digital television system features.
DigiCipher~ II is a proprietary system developed by
General Instrument Corporation of Horsham, Pennsylvania,
U.S.A., the assignee hereof. This system includes
features that are specific to the cable television
environment for downstream and upstream communications.
The features supported by the core set-top system
software 20 include, without limitation, service
acquisition (e. g., acquisition of a pay-per-view movie),
system information management, set-top configuration and
control, return path for polling, download capability
including authentication and authorization, and non-
volatile memory management.
The core set-top system software 20 also includes
conditional access system drivers (CABIOS), which are
used to provide security and access control. This
component supports the features of object
authentication, object authorization, resource
authorization, cryptographic tool kit, and baseline
privacy key exchange. The interface layer for the
cryptographic tool kit (Crypto Toolkit) is the Public
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Key Cryptography Standards (PKCS) 11 standard.
More specifically, the core set-top system software
20 provides the services that allow the set-top to exist
in a communication (e.g., cable television) network. As
noted above, the functions of this software include:
Message reception and distribution - This software
component receives messages over a control channel or
through an in-band channel, and distributes them to the
appropriate software process for interpretation and
processing.
System information processing - This component
interprets the System Information provided by the
protocol (e. g., Advanced Television Systems Committee
(ATSC), or Digital Video Broadcast (DVB) standard)
specifying the Modulation Type, Channel Map, Service
Maps, Service Descriptions, Service Components. This
information allows the software to find, reconstruct and
deliver the service to the user or application.
Configuration and control message processing - This
component interprets the configuration and control
messages sent to the set-top from, e.g., a cable headend
controller. This information is used to provision a
set-top to operate within the cable television system or
other applicable network. The component sets up the
set-top's features and provides the ability to control
the set-top operation remotely by the system operator.
Digital and analog service acquisition - This component
performs all of the necessary functions to 'tune' a
video/audio service to be presented to the television
viewer.
Conditional access subsystem - this component
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authorizes services and applications. Video services
are delivered to the set-top in an encrypted form. The
Conditional Access (CA) system compares authorization
information about the service with authorization
information that is delivered to the set-top. When a
service is deemed authorized, the CA system enables the
decryption of that service.
Download subsystem - this component acquires software
objects from the cable or other applicable network and
stores them in the set-top's memory. These objects may
include, e.g., software suites or applications. The
download subsystem determines if it is authorized to
accept the object and, if it is, then processes and
stores each segment of the object. Once the object is
stored, it is validated and can then be enabled to
execute either from, e.g., the headend control, or by
the operating system.
Return path subsystem - This component collects
purchase and diagnostic information and transmits it
back to the headend (or other appropriate system
operator site) upon command. This information is
ultimately sent to a billing system to enable billing of
services used by the set-top. The return path can be a
store-and-forward mechanism or an on-demand interactive
mechanism.
Diagnostic Data management subsystem - This component
collects and manages data which can be used to diagnose
the state of the set-top, allowing for remote
determination of the operation and health of the set-top
software. This data is made available to the OS for
display to the user or installer. It is also made
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available to the return path subsystem for collection by
a computer at the system operator's site (e.g., at a
cable headend) .
The CABIOS (Conditional Access Basic Services)
provides conditional access services above the normal
service access control, including:
Object Authentication - This function authenticates a
software object to determine that the object is the
intended object. Such authentication is accomplished,
for example, by matching a signature delivered with the
object.
Object Authorization - This function authorizes objects
to be loaded and executed in the set-top. It uses the
conditional access hardware to determine the
authorization status of the set-top.
Resource Authorization - This function authorizes the
use of set-top resources through the conditional access
hardware.
Baseline Privacy Key Exchange Services - These functions
support the key exchange requirements of the Cable modem
system, which may conform to the Data-Over-Cable Service
Interface Specifications (DOCSIS).
Cryptographic Functions - These functions provide a
basic cryptographic toolkit for use by the application
operating system and applications within the set-top.
As indicated above, a typical cryptographic tool set
follows the PKCS 11 standard, although other standards
can be used.
The graphics, audio and video subsystem 22
includes, in a preferred embodiment, two-dimensional
(2D), three-dimensional (3D), and video libraries
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working on top of a graphics display driver. Such
display drivers are commonly available from various
vendors such as ATI Technologies Inc. of Thornhill,
Ontario, Canada. Subsystem 22 provides a standard API
to which middleware providers can be ported, and enables
video to be viewed combined with graphics. More
particularly, the analog or digital video is combined
with a graphics overlay to present a combined view to
the user. This subsystem 22 also provides audio, which
can exist in multiple modes, such as stereo and surround
sound. The audio subsystem can also support record and
playback of audio files.
The network communications stacks 24 provide
standardized networking stacks to facilitate web
browsing and communications with external devices. This
subsystem 24 includes many standardized network
protocols which can be delivered over multiple
communications paths. The stacks can comprise, for
example, Mentor/Microtec's CNX communications extension
to the VRTX operating system, available from Mentor
Graphics Corporation of Wilsonville, Oregon.
This subsystem 24 resides on top of the
communications drivers (e. g., Ethernet and DOCSIS
drivers) and provides, for example, a Berkeley sockets
(Berkeley Software Design, Inc.) interface to protocols
such as Transmission Control Protocol (TCP)/Internet
Protocol (IP) (e. g., a TCP/IP interface over a DOCSIS
modem or over an Ethernet device), User Datagram
Protocol (UDP), Address Resolution Protocol (ARP),
Internet Control Message Protocol (ICMP), Dynamic Host
Configuration Protocol (DHCP) Client, Domain Name System
(DNS) Client, and Point-to-Point Protocol (PPP) (dial-up
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uses CCP, Linlc Control Protocol (LCP) and Internet
Protocol Control Protocol (IPCP) protocols).
For the set-top hardware 34 to operate the set-top
box for its intended functions, various drivers must be
5 provided, as well known in the art. These are depicted
in the Figure as low level device drivers 32, which, in
accordance with the present invention, are interfaced to
a driver model used by the core set-top system software
via device drivers-to-driver model interface 30.
10 The interface 30 separates the details of the
driver model environment from the core system software
20. The interface 30 is used to isolate the device
drivers 32 from the specifics of the driver model
provided by the operating environment. The low level
15 device driver software 32 is hardware-specific and
portable across operating environments. The driver
model interface 30 ties the hardware-specific device
driver 32 to the OS by providing the OS's desired
interface to the driver.
20 Device drivers are provided for each device
supported on the set-top. These include a graphics
driver, which may be written, e.g., on an ATI Hardware
Access Provider (HAP) layer available from ATI
Technologies, Inc. A graphics library for use in the
set-top can written on the HAP. Other typical set-top
device drivers include a communications driver, the
tuner (e. g., a combination of the General Instrument
DOCSIS tuner and Quadrature Amplitude Modulation (QAM)
code), serial ports (using, e.g., an IEEE 1394 high
performance serial bus), parallel ports, Ethernet ports,
Universal Serial Bus (USB) ports, Light-Emitting Diodes
(LEDs), Keypad and/or Keyboard drivers, a DOCSIS driver,
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such as the Broadcom DOCSIS driver available from
Broadcom Corporation of Irvine, California, U.S.A., and
a smart card driver. A smart card may be used in the
set-top for consumer purchasing applications such as on-
line buying. Each device in the set-top requires a
driver function to operate.
It should now be appreciated that the present
invention solves the problem of enabling core set-top
software to be compatible with multiple .set-top
operating environments. With the software architecture
provided by the invention, it is not necessary to port
the core software to different operating environments by
rewriting code specific to each environment or through
an abstraction layer. Instead, a unique device drivers-
to-driver model interface is provided together with a
kernel abstraction component that overcomes portability
issues and provides for a clean interface between layers
in the architecture. The invention can be implemented
using object oriented techniques, such as C++ or Java
programming, although the invention is by no means
limited to such an implementation.
The combination of the components described herein
provides a basis for set-top software to enable advanced
features of an advanced set-top box implementation.
Each of the components provides necessary functions
required by an advanced set-top terminal. The novel
architecture of the invention provides the benefits of
reuse and portability of the core set-top software to
alternate operating environments, thereby allowing well-
understood and previously tested software components to
be reused. The architecture also allows implementations
in alternate operating environments to be quickly and
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straightforwardly provided.
Although the invention has been described in
connection with various specific implementations, it
should be appreciated that various adaptations and
modifications can be made thereto without departing from
the scope of the invention as set forth in the claims.
