Design of IPTV set-top box based on EM8620

Traditional TV services are consistently operated in a one-way broadcast mode. With the advancement of technology, people are increasingly hoping to implement two-way interactive functions in TV. Through interactive communication, operators can know the needs of users in a timely manner, and end users also It can change the single passive information receiving mode in the past and participate more in business operations. The recent emergence of iptv (Internet TV) made this wish possible. It is a fusion of TV and network communication technology, with ip as the transmission channel, which can provide users with a wider variety of interactive video and audio including TV. service.

In the iptv system, the user terminal set-top box is a very critical device. It is not only a terminal for watching TV programs, but also a platform for information aggregation and interaction. It is considered to be an important part of the future home multimedia center. An iptv set-top box design based on em8620 chip, which can realize interactive TV service through network, support mpeg2, mpeg4, vc-1 (wmv9), real and other video compression standard decoding, with TV program recording, digital copyright protection , dvd playback and other functions.

1 hardware design

1.1 Analysis of design requirements

Through the detailed analysis of the iptv business features, the four requirements of the fpga set-top box hardware design are summarized:

(1) With network access function, it can access the Internet by means of lan, dsl, etc., and supports various network protocols such as tcp/ip, ftp, rtp, rtsp, rtcp, and igmp.

(2) Support multiple video compression formats. Currently, mpeg2, mpeg4, vc-1 and other standards are used in iptv. Some operators even use it in crossover, which is quite different from traditional digital TV using a single mpeg2 standard. Therefore, the more compression standards that the designed set-top box can support, the more flexible the business development and the wider the scope of use of the product.

(3) It has perfect multi-proliferation business design, including video on demand, electronic voting, interactive games, web browsing, online games, etc. The proliferation business is the key to the profit of network TV, so we must fully consider the various proliferation services when designing the set-top box. Extended application.

(4) Select a low-cost dedicated hardware platform. A set-top box is different from a general-purpose computer. It is an embedded system. Low cost, low power consumption and stability are the principles to be followed by hardware design. Some early iptv set-top box designs use a high-performance general-purpose processor architecture based on Intel. Performance is good, but it is ultimately difficult to be recognized by the market and operators in terms of power consumption and cost.

1.2 em8620 hardware platform

The design uses a low-cost but relatively feature-rich integrated chip, the em8620, as the hardware platform. It is the latest multi-format decoder chip designed by Sigma Packaging for digital video communication, and a 166mhz 32-bit rsic processor. It has a rich audio and video interface, in addition to the pci bus controller and ide bus interface, which can realize network access, usb peripherals and ide peripherals (such as hard disk, optical drive) access. Figure 1 is a block diagram of the logic unit of the chip. Its main functions and features include:

(1) It can simultaneously support the decoding of two standard definition TV programs and realize picture-in-picture. ;
(2) Video supports mpeg2, mpeg4 standard definition and HD decoding, and supports standard definition decoding of vc-1 and real;
(3) Support dvd format signal decoding;
(4) Audio support dolby ac3, mpeg1 and mpeg2 layer 1, 2, 3, mpeg2 bc multi-channel layer 1, 2, 3, mpeg2 aac, mpeg4 aac, windows wma;
(5) has an adaptive deinterlacing function;
(6) osd function with de-flicker filtering, color support 32 bits/pixel;
(7) having four image layers such as video, osd, sub-image and cursor;
(8) A bus control interface with pci2.1;
(9) using 2d graphics acceleration;
(10) With ide interface, it can connect optical drive and hard disk device to realize TV recording and program storage;
(11) ntsc/pal composite video and s-video component output with optional macrovision anti-recording protection;
(12) with ypbpr / rgb component video output with optional macrovision anti-recording protection;
(13) has 3 channels of i2s serial digital pcm audio output to achieve 5.1 channel surround sound;
(14) With spdif (iec60958) digital audio output.

1.3 Design principle

Following the design requirements of the iptv set-top box, the block diagram of the hardware design with em8620 as the core is shown in Figure 2. It includes several different data processing modules.

1.3.1 pci bus

A 10/100m Ethernet controller (ctl8100) and a usb2.0 host controller (vt6212) are connected to the pci bus for network access and usb device access.

1.3.2 10/100m Ethernet Controller

The 10/100m Ethernet controller uses Realtek's rtl8100, a highly integrated, low-cost single-chip Ethernet controller with acpi power and Wake-on-LAN functionality, using magic packets and wake-up The frame method can easily realize network management and maintenance, so it can realize an ideal embedded network solution. It also has pci/mini-pci interface and 10/100mhz network bandwidth adaptive function, and is compatible with pci2. .2 and pc99/pc2001, pci storage space or i/o space mapping data transmission and other functions.

1.3.3 usb2.0 main controller

The usb2.0 main controller uses VIA's vt6212, which is a four-port usb2.0 control chip that supports transmission speeds up to 480mbps and uses dynamic stop clock control to reduce power consumption. Vt6212 provides high-speed data transmission by means of the enhanced host controller interface. It is backward compatible with low-speed usb1.1 data transmission through the universal host controller interface. In addition, tv6212 also supports 32-bit card bus. Mode, can be used with the pcmcia interface as a usb 2.0 hub, increasing the number of peripheral access.

1.3.4 Video output

The em8620 can provide both analog and digital video signal output. The analog video is directly output by composite (cvbs), component (s-video and yprpb), and the macrovision technology can be used for anti-piracy recording protection in the output. Digital video (24bit rgb) is connected to the dvi signal synthesis chip (sil164), which is encoded as dvd format and output.

1.3.5 dvi signal synthesis

Dvi is a very widely used digital video interface that can be used for both high/standard definition digital TV displays and general computer monitor displays. Here, silicon image company's sil164 is selected to implement dvi signal synthesis and transmission. The sil164 is designed with paneilink digital technology and supports resolution range from vga to uxga (640×480-1600×1200) with data rate range of 25-165mbps, 12bit (half-pixel clock edge) and 24bit (true color support). Two design modes, support for i2c bus control, hot swappable, fully compatible with the dvi1.0 specification.

1.3.6 Audio output

The em8620 can provide two serial digital audio signals, such as three-way i2s and one spdif. Each i2s signal carries two channels of pcm data. After three channels of i2s are connected to the audio dac, they are converted into six channels of analog audio. For 5.1-channel surround sound of dolby ac3; spdif serial digital signal output directly, can carry two pcm audio or compressed 5.1 channel dolby ac3 audio.

1.3.7 Peripheral bus

The peripheral bus is connected with an ide hard disk, a dvd optical drive and a flash memory. The ide hard disk is used to implement a personal video recorder function. The user can conveniently store the played circuit program to the ide hard disk, and can also be used for storing the multimedia service through the proliferation service. Download various other data; dvd optical drive can make the set-top box realize dvd playback function, the role of flash memory is very important, used to store the operating system software of the entire set-top box. Although it is also possible to install the operating system to the ide hard disk, the stability of the ide hard disk is far less than that of the flash memory, and it is also vulnerable to other applications, especially viruses, which can easily cause a system crash.

1.3.8 fp/vfd and infrared signal reception

Fp/vfd is used for the front panel control and status display of the set top box, and the infrared signal receiving is used to receive the control signal sent by the remote controller.

1.3.9 uart

Although iptv has a two-way service channel, it can implement the copyright protection of the program by means of authentication. However, in view of the fact that the conditions in the digital TV are currently received by the smart card method, in order to protect the compatibility of the system, a smart card based on uart is still designed here. A communication module that supports the use of smart cards for key decryption.

2 software design

The software mainly includes an embedded operating system and various types of drivers and application software. Because of the excellent portability and extensive compatibility of Linux, the operating system is implemented by μclinux in this solution, and the application software mainly includes electronic program guide, digital copyright protection and conditional access, browser, graphical user interface and software. Decoding module, etc.

2.1 Embedded Operating System

Cclinux is an embedded operating system designed for mmu (memory management unit). The kernel is developed from the linux2.0 kernel. Compared with the standard linux, it inherits the main advantages of strong work stability and powerful network functions. In addition, it has the characteristics of small footprint and high execution efficiency. Since the iptv set-top box needs to implement various network-based proliferation services, the requirements for network communication protocols are relatively wide. μclinux includes various network protocols such as tcp/ip, which can support the current Various ip-based services, and it also has good openness, any new protocol can be easily added to the kernel, with the ability to continuously upgrade and expand.

When using μclinux for software design, a problem that needs to be considered is memory management. Since em8620 does not have mmu management memory, μclinux cannot use virtual memory management technology. Memory access should be directly addressed. All programs access addresses. The actual physical address, after the operating system memory space is lost, the processes in the system actually share the same memory space. Therefore, when designing multi-process tasks, special attention should be paid to memory protection to prevent program operations from overflowing. Specifically, when each process is initialized, μclinux allocates a continuous stack address space according to the user's application, and then all data operations in the process are completed in this memory space, so the developer must perform each task. The maximum memory space required by the process is correctly estimated and allocated. Once the generated data space is larger than the allocated memory space, a memory overflow occurs, which infringes the address space of other programs, resulting in abnormal operation of the program, which may result in serious system breakdown.

One of the biggest shortcomings of traditional Linux is that after the system is shut down abnormally, the hard disk fragmentation is often generated, so that the operating system cannot boot normally. Here, the μclinux is compiled and burned to the flash using the flash kernel boot mode, which avoids the above. Disadvantages.

2.2 Application Software

2.2.1 Electronic Program Guide

The electronic program guide is a direct way for users to obtain broadcast information of TV programs. From the survey of existing digital TV users, the electronic program guide is currently the most popular function for users. The electronic program guide generally includes TV program list, program introduction, The current program information display, program scheduling and other links, usually its design is based on the middleware or custom programming software modules, the process is complex, the flexibility is poor. Here, a browser-based electronic program guide design is adopted, and the television program information is transmitted in html mode or xml mode. After the set top box is received and displayed by the browser for viewing by the user, the style and browsing manner are highly flexible, due to other types. The proliferation services such as web browsing and TV shopping require browsers, so using the browser does not increase the overhead of the system.

2.2.2 Digital Copyright Protection

Digital copyright protection design is divided into two types, one is for the protection of recorded programs, and the other is for the protection of live broadcast programs. Because the set-top box has the function of personal video recorder, users can conveniently record the TV programs broadcast in real time. Go to the hard disk and copy it out via the usb interface for distribution. In order to prevent such pirated copying, a strict digital copyright protection module is designed. When the user performs recording, the program stored on the hard disk is encrypted, and the encryption key is generated by the hardware information unique to each set-top box, so that even Copying the program to other set-top boxes of the same type can not be played, thus achieving strict copyright protection function. For the encrypted program broadcasted in real time, the smart card-based working mode is followed, and the key data stream transmitted by the ip network is first extracted. It is sent to the smart card through the uart interface for decryption. After decryption, the control word is stored in the memory and destroyed immediately after use to prevent theft and cracking.

2.2.3 Graphical User Interface

In order to conveniently operate the ide hard disk and other interfaces, the user interface is provided here. It uses the minigui engine. After the interface is started, the user can operate it easily through the remote control or by connecting the usb mouse/keyboard.

In addition to the above application software, it can also support various java and flash programs to run, which is convenient for TV shopping and online games. In addition, it includes a series of multimedia playback programs such as wmv9 and real for various types of network audio and video programs. And local dvd disc playback.

2.3 Software debugging

Software debugging is divided into two steps: kernel debugging and application debugging.

2.3.1 Kernel debugging

A simple way to debug the kernel is to use the jtag writer to write the μclinux directly into the flash. This debugging process requires repeated flashing of the flash. The process is cumbersome and time consuming. In order to overcome the above shortcomings, this is written for em8620. A bootloader program that downloads μclinux to memory via Ethernet. After the kernel debugging is stable, it is burned to the flash, which can effectively simplify the entire debugging process and improve work efficiency.

2.3.2 Application debugging

The development and debugging of the application adopts two methods. One is a program with less functions and less resources, and is directly developed and debugged by using telnet to connect to the set-top box through Ethernet. Because μclinux supports multi-user working mode, many different developers can log in to the system for their own debugging without affecting each other. However, as an embedded processor, the computing power of em8620 is limited. If too many tasks will affect debugging. Speed, for this reason, the application that consumes a large amount of resources needs to adopt the cross-compilation method, that is, the debugging and compiling of the program is completed on the faster PC, and then the gnu tool is cross-compiled into the target code based on μclinux, and then passed through the ether. The network is transmitted to the set top box for operation.

At present, the development of iptv is in full swing. TV and telecom operators around the world are stepping up efforts to build iptv. The demand for iptv set-top boxes will expand rapidly in the next few years. The em8620-based iptv set-top box realized in this paper has a rich functional interface. And can support high-definition and standard definition multiple video format decoding, in line with the technical requirements of future iptv business development, is a long-term effective solution.