Design of ARM and STi5x Digital Network Set Top Box

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Abstract : This paper designs a digital network set-top box based on ARM9 and Sti5518. In the paper, the traditional digital set-top box and digital network set-top box are compared. It is found that the digital network set-top box adds ARM9 core CPU module and dual-port RAM module on the basis of the traditional digital set-top box. After the digital network set-top box is designed and implemented, it can not only be completed. All the functions of a traditional digital set-top box, and the ability to store TV programs, connect to the Internet, and other functions that can be done over the Internet. The hardware logic design of the digital network set-top box is also given in the paper.
Keywords : digital network set-top box; dual-port RAM; ARM9 core; STi5518

1 Introduction

With the deep development of computer technology, the advent of the post-PC era, the convergence of cable TV networks, the Internet, and telecommunications networks has become an inevitable trend of the times. However, since the three networks have great differences in data transmission methods, it is still not possible to integrate the three networks on the technical level. Therefore, to achieve the integration of the three networks, it is necessary to resort to similar network set-top boxes ( IPTV) equipment to complete the integration of the three networks. China's cable digital TV standard adopts the European DVB-C standard. Although there are digital TV set-top boxes on the market, they all use some complete set-top box solutions of enterprises, such as the DVB-C set-top box solution of Philips. The tuner and channel decoder use TDA8274 and TDA10023 [1] respectively , the CPU adopts MIPS core PNX831X; the US ST company's STi5518 CPU set-top box solution [2] , its CPU core is ST20, etc., these complete digital set-top boxes The central control module of the solution tends to focus on the functions of demultiplexing, video decoding, audio decoding and PAL/NTSC encoding of digital TV signals, so the recording and Internet functions of these set-top boxes are very weak, and because of them It is not well embedded in common embedded operating systems, so many applications are very computationally intensive and many functions are difficult to implement.

2 Comparison of traditional digital set-top boxes and digital network boxes

Digital television systems are divided into the transmission of digital television, the transmission of digital television and the reception of digital television. The transmission of digital TV mainly includes the production of digital programs, audio and video coding, and its standard adopts MP@ML of MPEG-2 standard, and its data compression rate can reach 30~50 times, so as to facilitate the storage and transmission of information; Program multiplexing to increase channel transmission capacity; signal modulation, different transmission methods use different modulation methods. There are three forms of signal transmission, satellite transmission, and modulation method using four-phase shift keying (QPSK). Terrestrial broadcast transmission, its modulation method uses DMB. The cable transmission mode uses quadrature amplitude modulation (MQAM). The logical structure of a traditional digital set-top box is shown in Figure 1:

Figure 1 Traditional digital set-top box logic structure

This design combines the digital TV demultiplexing module STi5518 and ARM9 core technology organically to design a set-top box based on ARM9 and STi5518 cable digital network. The tuner and channel decoder at the front end of the cable digital set-top box use Philips TDA8274 and TDA10023, the demultiplexer uses STi5518, and the ARM9 core uses Samsung S3C2410A. The data communication of the two CPUs uses IDT's dual-port RAM. Its hardware structure is shown in Figure 2 below:


Figure 2 Digital network set-top box logic structure

Compared with the traditional set-top box, the digital network set-top box only has more ARM module and dual-port RAM module, but the function is greatly increased. The main function of the digital network set-top box is to complete the reception of the digital television program and save the processed program signal. To the storage device and to the display device display, while being able to complete the connection with the Internet. This is done in several steps: the silicon tuner of the set-top box receives the RF signal, the downlink is converted to the intermediate frequency signal, amplified, and then sent to the AD converter for analog to digital conversion, and then sent to the demodulator module for demodulation, output serial Or parallel transport stream (TS) in MPEG-2 format. This part of the function is mainly completed by Philips' TDA8274 and TDA10023 chipset, after the chipset's tuning, down-conversion amplification, AD conversion and output transport stream (TS).

After receiving the transport stream sent by the front end, the STi5518 demultiplexes and descrambles the MPEG-2 audio and video decoding, and then completes the PAL/NTSC&SECAM encoding and VGA conversion output for TV or CRT display. Audio encoding and Dolby 5.1 audio standard output. The front-end interface supports VCD, DVD, SVCD and CD-DA I2S, serial port, and supports I2C control interface. And the communication with the ARM CPU is completed through the dual port RAM.

The main CPU of the set-top box adopts Samsung ARM S3C2410A. The CPU can work at 203MHz, integrate Flash, SDRAM controller, hard disk interface, USB interface, I2C controller, multi-serial port and Internet interface. Its main function is to control the entire digital network set-top box, complete the connection with the Internet, store TV programs, complete video on demand and other functions. Data exchange with the STi5518 is accomplished using dual-port RAM, and control of the front-end demodulator is accomplished using I2C.

3 hardware structure of network digital set-top box

3.1 Digital network set-top box front-end hardware design

The front end function of the digital network set-top box is to complete the reception of the radio frequency signal, the down conversion amplification, and the channel decoding output transport stream (TS). The RF receiver and channel decoder are based on the Philips TDA8274 and TDA10023. The TDA274 is a powerful RF integrated circuit that embeds a low-noise input amplifier and provides an image rejection and mixing down-conversion to IF for processing RF signals. It is filtered and sent to the channel decoder TDA10023. Channel decoding function.

The TDA10023 is a cable channel decoder that provides 4, 16, 32, 64, 128 and 256 quadrature frequency demodulation with an IF signal input that converts analog signals into digital signals via an internal 10-bit A/D converter. The chip includes two forward error correction encoders (FECs). In DVB-C mode, MPEG-2 sync bytes are used for error correction, which can correct 8 error bytes. In MCNS mode decision, soft decoding is used. The device corrects random channel errors, and the IF signal sent to the TDA10023 undergoes A/D conversion, QAM demodulation, forward error correction, filtering, and finally serial/parallel transmission.

3.2 Demultiplexing and audio and video processing

The digital network set-top box CPU adopts ST's dedicated demultiplexing and audio and video processor chip STi5518. The STi5518 is a 32-bit high-performance CPU specially designed for demultiplexing, descrambling and MPEG-2 of DVB digital TV signals. A dedicated chip for audio and video decoding. Its instruction cache and data cache are set to 2KB each, and another 4KB SRAM can be set as data cache. It supports PAL/NTSC/&SECAM coded output, and audio and video decoders support multiple encoding formats. The front-end interface is compatible with DVD, VCD, SVCD, and CD-DA. The hardware TS demultiplexer supports serial/parallel input and integrates a rich peripheral interface. It supports ANSI C compilers and libraries, which brings great convenience to development. .

The STi5518 receives the transport stream from the front-end output in serial or parallel mode, and its internal demultiplexer demodulates different program channels, extracts the corresponding audio and video streams and data streams, and outputs the corresponding MPEG-2 audiovisual elementary stream. And some data payloads. The restoration of digital information by the MPEG-2 decoder and the corresponding parsing software. For encrypted television programs, the conditional receiving module can descramble the audio and video through the smart card. The MPEG-2 decoder is used for audio and video decompression, and the analog audio and video signals are restored by a video encoder and an audio encoder. Demultiplexing and audio and video decoding STi518 extended function module is shown below:


Figure 3 demultiplexing, audio and video decoding module

In the STi5518 module, the E2PROM is used to store configuration parameters during the working process, the synchronous memory SDRAM is used to run the program, the Flash is used to program the startup program, and the smart card interface is used to complete the conditional receiving function. At the same time, the expansion module outputs the signals required by the digital TV and VGA display, and the dual port RAM is used to complete the communication between the STi5518 and the ARM board.

3.3 central processor ARM9 module

The S3C2410 is a CPU based on the ARM9 core of the reduced instruction set designed and developed by Samsung. The operating frequency can reach 203MHz and has a wealth of peripheral components, including: memory management unit MMU, 16KB instruction buffer and 16KB data buffer. [3] , memory controller (SDRAM controller), NAND Flash and NOR Flash controller, 4-channel external DMA request control, 3 serial ports, SD memory card read interface, 2 USB ports (1 USB Host interface and 1 USB device interface), 5 pulse width modulation timers, watchdog timer, 117 general purpose I/O ports (24 of which can be used for interrupt requests). Because the S3C2410 has such a powerful peripheral control component, it is widely used in electronic products. The logical structure of its ARM9 expansion board is shown in Figure 4 below:


Figure 4 Logical structure of the ARM9 expansion board

The ARM9 expansion board consists of S3C2410 CPU, 64M flash memory, 64M synchronous memory, keyboard and USB interface; the components for processing digital TV signals are mainly composed of hard disk, Internet interface, infrared transmission and reception and dual port RAM. The main function of the module is to complete the storage of digital TV programs, connect to the Internet, control the infrared, control the front-end tuner through the I2C interface, and complete the data exchange with the STI5518 through the dual-port RAM. The 64M flash memory in the system is used to store the CPU startup program and Linux operating system; 64M synchronous memory is used to run the operating system and applications; the keyboard is used to input numbers; USB interface is used to connect external USB devices, such as USB mobile hard disk, USB Printers, etc.; hard disks are used to store digital TV programs and other information, data; Internet access modules are used for broadband access to the Internet; infrared modules control the transmission and reception of remote controls, select TV programs or other functions; dual-port RAM To achieve data exchange with STI5518.

4 Software and features of digital network set-top boxes

Since the embedded system software and the microprocessor are closely related, it is usually described by a layered model. The software hierarchy is divided into a firmware layer, a driver layer, a middleware, and an application layer from the bottom up, so that once the hardware module changes, Software modifications only occur in the firmware layer associated with the hardware. The middleware and application layers can remain unchanged, reducing programming effort and software development time. The principle of hierarchical construction follows: a module of a certain layer can call the lower layer module, and at the same time can be called by the upper layer, and generally cannot be called between the same layer.

The hardware of a digital network set-top box is equivalent to a Pentium III computer and a digital set-top box, so its functions can both complete the functions of the computer and complete the functions of the digital set-top box. The main functions of the digital network set-top box are:

1) Digital TV program reception 2) DVB public descrambling algorithm and conditional reception 3) Support PAL/NTSC/SECAM 4) Support MPEG-2 image and MP3, Dolby 5.1 sound quality 5) Distance education 6) Pay-per-view TV

7) Electronic Program Guide 8) Internet Access [4] 9) Digital TV Program Storage 10) Video on Demand (VOD)

11) Interactive TV games, etc., it can be seen that the function of the digital network TV set-top box is very powerful.

5 Summary

The author's innovation is to complete the design of the digital network set-top box hardware platform based on ARM9 and STi5518. In this paper, the traditional digital set-top box and digital network set-top box are compared. At the same time, the hardware logic block diagram of the digital network set-top box, as well as the software model and function are given. After the design is realized, not only can the functions of the traditional digital set-top box be completed, but also the function of storing and connecting the Internet to the television program can be completed. It is reasonable to believe that with the advent of the digital television era, the design can be widely applied.

[1] Philips Electronics Co., Ltd. TDA827x User's Manual [OL].2003.

[2] ST Electronics Co., Ltd. Sti5518 User's Manual [OL].2001.

[3] Zhang Ying, Lin Xiaokang. Embedded Gateway Design Based on ARM and FPGA[J]. Microcomputer Information, 2006, 8-2: 32~35.

[4] Hou Dongqing, Zhao Jin. Design of remote data acquisition platform based on ARM9 and GSM [J], Electromechanical Product Development and Innovation. 2006, 2: 84~85.

[5] Samsung Electronics Co., Ltd. S3C2410X Microprocessor User's Manual [OL].2003.

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