Electronic Design

Controller IC Is Gateway To Multiple, Secure A/V Sources

Multiple transport ports, plus a variety of demultiplexing and descrambling algorithms in a single IC, fulfill the requirements of personal video recorders and set-top boxes.

The TL8xx family of set-top box/personal video recorder (STB/PVR) controller ICs consist of single-chip, multiple-transport, descrambler/controller devices. Due to their array of on-board descramblers and demultiplexers (demuxes), they are highly versatile devices, well-suited to perform as gateways for the flow of secured and encrypted audio, video, and interactive data streams. These ICs may be used to manage arriving and departing data streams—into and out of set-top boxes, storage devices, digital TVs, PVRs—as well as home media servers that connect to broadband cable, satellite, terrestrial, and IP networks.

In particular, the ICs from TeraLogic Inc. of Mountain View, Calif., have been designed to address the needs resulting from the rise in demand for PVR designs. These systems enable live TV channels to be paused and manipulated in other ways. Examples of this manipulation are pause, record, fast forward, and rewind. New systems also enable picture-in-picture (PIP).

The STB/PVR controller IC is said to be the first IC with the integrated functions to serve as a gateway for smart-card controllers, IEEE-1394 interfaces, high-speed CPU bridge and memory controllers, PCI controllers, and other peripherals like hard-disk drives, UARTs, infrared (IR), and I2C. These capabilities are possible because the ICs bring together what in the past required many individual chips. In addition, the ICs act as gateways for the TV or STB by managing and controlling multiple transport systems.

Traditionally, a separate north bridge chip would interface to the CPU and the PCI bus. Another chip would perform the demux function. There also would be a descrambler chip, and at least one or more chips to supply the interfaces, such as IDE.

On board the STB/PVR controller ICs are a programmable transport layer RISC engine, disk controller, descramblers for secure transactions, and demuxes. In addition, the devices contain a set of descrambling technologies designed to address the conditional access (CA) systems in worldwide use today. Therefore, the ICs can process their encrypted transport streams, decrypting them by using one or more of the devices' on-board algorithms.

Included too is a flexible arrangement for switching between the descramblers, demuxes, and various ports. In fact, due to the multiplicity of access that it affords, the STB/PVR controller IC can be thought of as a large crossbar switch. By this feature, it becomes relatively easy to route data through the different demux and descrambling processing blocks. Because it also can simultaneously handle audio, video, and data streams, which are encrypted using various worldwide CA standards, these ICs can be considered a universal solution for CA.

Multiple Ports
The extraordinary flexibility of the STB/PVR controller IC is largely due to its ability to receive and manage four transport stream ports (Fig. 1). This unusual arrangement enables the IC to offer low-cost, flexible solutions for PVR applications and PIP, or any other configuration where transport streams are arriving from different sources. Incidentally, the four transport stream I/Os are compatible with a multitude of standards, including ATSC, ARIB, DVB, and DirecTV.

As an example of another application, a configuration could include receiving streams from satellite, terrestrial, digital VCR, and a hard-disk drive, all in a single, low-cost system. Or by adding the STB/PVR controller IC to an existing design, a standard set-top box can be upgraded to include PVR functions, PIP, or other more advanced, revenue-generating features.

There are two unidirectional ports—T/S 1 (in) and T/S 2 (in). One is designed to receive either parallel or serial streams, but the second only handles serial streams. These two ports are what enable the reception and management of two streams simultaneously for configuring features like PIP or watch-and-record (where the multiple ports enable the viewer to watch the input from one port while recording the other).

The third port, T/S 3 (in and out), is bidirectional, enabling transport streams to be either read or written across bidirectional interfaces such as the IEEE-1394. This interface is rapidly becoming the de facto interdevice connection for various components in the digital home of the future. It may become a common interface in set-top boxes, although it's perceived as expensive.

Following descrambling and demuxing, the output port (T/S out) feeds any one of the three arriving input streams to a source decoder IC, like the TeraLogic TL850 decoder. Any of the arriving transport streams coming in can be routed through the chip through any of the different blocks. Or, an arriving transport stream can skirt around all the processing blocks and go directly to a DTV decoder via transport out.

The other I/O port is included for I2C, SmartCards, IR, GPIO, and UART. I2C is normally used for controlling slower peripherals (400 kbits/s) like the tuner ICs and SmartCards for providing keys to the descramblers, IR for I/O to/from an infrared remote control or keyboards, and UARTs and GPIO for miscellaneous I/O.

The on-chip descramblers are an essential feature. They decode the encrypted data stream arriving with content copy protection, which is often the case in a set-top box or a TV—pay-per-view movies or personally addressed data, for instance.

To decode a stream into the clear, both the correct descrambling algorithm and the correct key are required. The combination of the key and the descrambling algorithm enable the STB/PVR controller IC to decrypt the transport stream so that it can then be fed to the demultiplexer and sent on to the decoder. TeraLogic believes that the STB/PVR controller IC has more on-chip algorithms than any other on the market.

There are two descramblers. Each can decrypt an arriving transport stream and deliver video, audio, and data content in the clear—regardless of whether the stream is arriving through cable, terrestrially via a network interface module, or through an external set-top box. In the case of terrestrial signals, many arriving programs are "free to air," so they aren't encrypted. But this role is changing, as broadcasters seek further revenue-generating services. The descramblers support a variety of worldwide descrambling algorithms, including DVB, DirecTV, DES-ECB, MPEG DES, Triple DES-CBC, and Multi-2.

As time goes on, there will likely be more protected content. A common example today is pay-per-view movies, where streams arrive encrypted and once payment has been confirmed, the set-top box or TV is empowered to decrypt the protected stream.

A descrambling key can be supplied by a SmartCard. Alternatively, in the case of open cable systems, the whole stream is passed through a PCMCIA-form-factor card that's installed in a point of deployment (POD) module.

There are either one or two demultiplexers. Each one receives an encrypted or else a decrypted stream of audio, video, and data, separates out the information by type, and feeds each to a buffer. The demultiplexers are microprogrammable engines, so their algorithms can be changed whenever new standards come out or if there arises a need to change the behavior of the demultiplexing unit. Thus, the STB/PVR controller IC isn't rendered obsolete due to changing transmission standards. Additionally, it can be enhanced even further for proprietary PVR systems.

A Plethora Of Buses
The STB/PVR controller IC has been configured with a unified memory architecture (UMA). This enables both the external CPU and the STB/PVR controller IC to share identical memory via the 32-bit SDRAM interface. The memory controller, which is effectively shared by the CPU and the STB/PVR controller IC, unifies the memory for the STB/PVR controller chip and anything else connected to it that needs memory. The benefit is that it prevents memory chunks from being scattered around the system by concentrating all memory into one place. Therefore, the UMA aids in holding down the cost of the overall system.

Consequently, to access its memory, the CPU actually goes through the STB/PVR controller IC with the latter acting as memory controller. A 16-bit local bus connects to Flash and EPROM and controls fast peripherals like IEEE-1394 devices and open cable POD modules. In addition, the IC acts as a bridge between the CPU and PCI bus, enabling access to a wide variety of inexpensive PCI peripherals.

A dual-channel IDE interface provides for the connection of up to two disk drives to the IDE bus. Both drives can then be used for storing incoming (or outgoing) transport streams in PVR appliances.

There are two SmartCard interfaces. They are used for CA applications to handle encrypted data arriving on one or more of the transport streams or from the disk drive. Each SmartCard interface functions in conjunction with the on-chip descramblers and perhaps a POD module. The key contained in the SmartCard authorizes a descrambler to decipher the arriving encrypted transport stream producing clear video, audio, and data.

The PVR I/O port is the key feature of the STB/PVR controller IC because it allows transport streams or elementary streams to be captured for viewing later, or for a pause-and-play capability. Elementary streams are the streams delivered by a demux.

The PCI Bus is a general-purpose bus for interfacing with other components in the system. For a long time, the PCI Bus has been perceived as solely PC-oriented. But over the past several years, it has become well accepted in the consumer electronics industry. Plus, now that such a large number of PCI-style components are in the marketplace, it has become quite convenient. Furthermore, PCI is an easy way to download software supplied by TeraLogic or written by the product designer, or to debug a DTV system.

The CPU Interface (SysAD Bus) is a standard 32-bit bus for connecting a MIPS-style microprocessor. The STB/PVR controller IC is compatible with MIPS microprocessors from a variety of manufacturers.

A Look At The Arriving Stream
The local bus controller is an 8- or 16-bit bus (selectable) that can be used for connecting peripherals of varying types—like Flash, EPROM, and other I/Os as required. So if there are miscellaneous I/Os that need to be controlled externally, the local bus is a good way to do it. For instance, ISAs and 68k-style peripherals can be connected and the STB/PVR controller IC local bus controller can be employed to access and control them. The local bus acts as a Flash bus, as well. This enables booting up the entire set-top box from one set of Flash connected to the local bus.

The ICAM Block is a dedicated descrambler for decoding systems that are enabled by New Data Services (NDS). It's their conditional access mechanism. In combination with a SmartCard, the ICAM block can be activated to descramble arriving NDS protected data streams. This is popular in Europe.

The signal arriving at a DTV tuner or set-top box is rf. The arriving rf signal from either a terrestrial, satellite, or cable source passes though a DTV tuner to a demodulator. As it passes through the front-end device, it's digitized and applied to one of the transport inputs of the STB/PVR controller IC. What arrives at the STB/PVR controller IC is a data stream chopped up into 188- or 130-byte packets. This complies with the ATSC standard for high-definition TV digital transmission, which defines this 188-byte packet. (This is the MPEG-2 transmission format, as well.) There also are proprietary standards, such as DirecTV, that employ 130-byte packets. In some cases, the format, as well as the length, varies. The algorithms stored in the STB/PVR controller IC are designed to comply with these various standards.

Pause-And-Play TV
Because the STB/PVR controller IC has enough ports and processing capability to receive multiple transport streams, it can readily handle PIP. For example, two tuners may be connected to the STB/PVR controller IC via the transport input ports (Fig. 2). The IC will process both streams simultaneously, decrypting one or both, as necessary. It can do this because it has two identical descrambler blocks. The composite PIP can then be forwarded to the demux and next fed to a DTV decoder for separating out the video, audio, and data.

Although PIP is relatively simple, there might be cases in a PVR system when the viewer wishes to use the third transport stream. For instance, in addition to having PIP active, there could be a requirement to simultaneously record data arriving at the third transport port for subscription/nonsubscription data devices.

A lot of the TV and set-top box companies have been quite surprised by the success of PVR manufacturers. They're eager to take advantage of the opportunities arising as PVR is catching on.

What is really novel about PVR is that it enables viewers to pause live TV. The arriving stream is decrypted, if necessary, and loaded directly onto a hard disk at the same time it's being read, fed through the demultiplexer, decoded, and forwarded on to the viewing screen (Fig. 3). There's only a fraction of a second delay between the content loading on the disk drive and the content being viewed on the screen.

The trick is to do it in real time—to write to the disk at the same time that it's being read. Once the viewer presses the pause control, the disk must continue recording the arriving transport flow in anticipation that the viewer will want to resume viewing shortly.

One might ask if the transport stream is always descrambled before it's demuxed. The designer has to decide whether to descramble the transport stream before or after it's demuxed. Descrambling a stream before it's fed to the hard drive is technically simpler. The content industry, however, prefers the descrambling to be delayed until after the streams are read from the disk. That's because, in theory, the disk drive is removable (Fig. 4). Therefore, it might be possible to connect it to a PC to permit unauthorized, decrypted content to be fed to an unauthorized screen.

Normally, the descrambler requires that a valid SmartCard be connected. The SmartCard, in effect, gives the descrambler a key that enables a particular algorithm. The algorithm uses this key as part of the descrambling mechanism. With the wrong key, of course, the viewer receives an unintelligible transport stream. These keys are automatically changed every so often.

Another technique for protecting the content involves stripping out the time stamp associated with the incoming data and manipulating the signals during demultiplexing. The PVR/STB controller can do this.

As video gobbles much disk space, the STB/PVR controller IC can manage arriving data to conserve the space. Say a particular disk drive can store 10 hours of video, but not all of the information arriving on any transport stream is of interest to the viewer. A 6-MHz TV channel may contain four or five standard-definition channels for instance. Instead, the 6-MHz band might carry a few standard-definition channels plus a data channel. Most likely, a viewer would wish to record only one of these channels. The arriving data stream can first be descrambled, if necessary, and then fed to the demux. There, the unwanted channels can be discarded so only the desired information is forwarded to the hard drive for storage (Fig. 5).

Price & Availability
There are three versions of the STB/PVR controller IC. Each comes in a 324-pin BGA package. The TL810 is designed for worldwide satellite applications—including DirecTV (USA), ARIB (Japan), and DVB (Europe). The TL811 also is suitable for worldwide satellite applications, but it will handle cable and terrestrial systems as well. This includes capabilities for ATSC, which is the U.S. standard for terrestrial digital transmission, and OpenCable for U.S. cable applications. The TL821 provides all of the capabilities of the TL811, plus a second demux, enabling simultaneous decryption from two transport streams. Prices range from $15 to $20 in high volume. The devices are available now.

TeraLogic Inc., 1240 Villa St., Mountain View, CA 94041; (650) 526-2000; fax (650) 526-2006; www.teralogic-inc.com.

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