Design and implementation of broadband information terminal based on DSP

1 Introduction

With the general trend of the integration of home appliances, communications, and consumer electronics, IPTV systems based on IP broadband networks have gradually become a hot topic. IPTV (Internet Protocol TV or Interactive Personal TV), also known as interactive network television, is a new technology that uses broadband network infrastructure, generally uses IP set-top boxes as the main terminal equipment, integrates multiple technologies such as the Internet, multimedia, and communications, and provides home users with a variety of interactive digital media services including digital television through IP protocols.

This paper proposes and designs a broadband information terminal based on Blackfin BF561. The terminal adopts the most active embedded system technology in the current computer field, with a high-performance DSP processor and embedded Linux operating system as the core [1], to design and implement the broadband information terminal.

The broadband information terminal is actually a low-end IPTV set-top box that can provide users with Internet information browsing and streaming video playback services. Under the existing network conditions (mainly network bandwidth) of domestic telecom operators, the terminal can present a relatively ideal media playback effect.

The terminal has been successfully put into commercial use and has been purchased in batches in Sichuan Telecom's rural informatization project. Currently, relying on the rural comprehensive information content platform deployed by Sichuan Telecom, thousands of this broadband information terminal have been promoted to rural areas across Sichuan.

2 System Design

2.1 Overall system design

The system design principle of the DSP-based broadband information terminal is shown in Figure 1. The uClinux operating system, audio and video decoding, various network protocols, embedded browser, streaming media player, and graphical user interface are all processed by BF561, and connected to external peripheral devices through multiple communication interfaces such as PPI, SPORT, and UART.

Figure 1 Schematic diagram of broadband information terminal system design based on DSP

Blackfin BF561 is a dual-core DSP processor launched by Analog Devices in recent years for high-end multimedia applications. As a symmetric multiprocessor (SMP) device, each core of BF561 has its own high-speed L1 instruction and data memory, and the two cores share 128KB of L2 memory. Each core can access a variety of peripherals, including video interfaces, serial ports, and timers. [2] In addition, the Blackfin processor also has high-performance processor cores, high-bandwidth DMA performance, an instruction set specifically defined for enhanced video processing, efficient control processing, hierarchical memory, dynamic power management and other features. [3]

In the design, one core of the BF561 handles all "MCU-type" tasks, such as graphics overlay, network management, and process control, while running the uClinux operating system; the other core performs the main DSP functions. We also put MP3 audio decoding in the core that handles "MCU-type" tasks, while the other core only performs MPEG4 video decoding. [4]

The following describes the system host from the perspective of video flow, audio flow, and network communication.

2.1.1 Reproduction of video signals

The video signal (video, text) transmitted from the network to the local is processed by the Ethernet controller, input to BF561 through the bus, processed into ITU656 format by MPEG4 decoder, and then converted into CVBS or Y/C signal by DAC, and displayed on the TV, thus realizing the reproduction of video images. DAC uses ADV7179KCP chip from Analog Devices.

2.1.2 Audio signal acquisition and reproduction

The audio signal (MP3) transmitted from the network to the local device is processed by the Ethernet controller, input to the BF561 through the bus, processed into ITU656 format by the MP3 decoder, and then converted into an analog audio signal by the DAC for playback on the TV. The DAC uses the WM8731S chip from WOLFSON. [5]

2.1.3 Network Processing

This system adopts a single network port design. The Ethernet controller uses SMSC's LAN9115 full-duplex 16BIT Ethernet controller, which can adapt to 100Base-TX/10Base-T.

2.2 System Software Design

The system software design principle is shown in Figure 2. The system application runs on the uClinux operating system with a kernel version of 2.6.11. The terminal application uses multi-process parallelism and inter-process communication mechanisms.

The system software consists of drivers, kernel tasks and user programs running on the uClinux kernel.

● Kernel driver

⑴ Network driver; ⑵ PPI video output module; ⑶ SPORT0-based audio driver; ⑷ Module for interacting with another core.

● Functional modules running in kernel mode

⑴ Video decoding module based on Timer drive;

⑵Complete audio Adaptive Jitter Buffer function and audio decoding.

● User program

⑴GUI user program interface module; ⑵Embedded browser module; ⑶RTSP streaming media player module; ⑷Decoder interface, RTP/RTCP module.

3 System Practice

The terminal has been realized and has been successfully launched to the market after several rounds of system testing and quality improvement. At this stage, it has excellent cost advantages and good scalability. As shown in Figure 3, it is a screenshot of the main menu of the terminal's graphical user interface.

In the implementation process, because it is a customized design for customers, the video decoding and audio decoding are set to MPEG4 and MP3 respectively. In fact, based on the DSP characteristics of BF561, other decoders such as H264 and AVS can also be designed in the system, so as to realize broadband information terminals that support multiple decoder formats and have good scalability. In fact, many partners of Analog Devices have successfully implemented CIF/D1 decoders of MPEG4/H264 on BF561.

4 Conclusion

The system has obvious cost advantages. The Blackfin uClinux operating system used is provided free of charge by the technical website (http://blackfin.uclinux.org) supported by ADI; ADI also provides continuous technical support to users (such as version upgrades, new project resources, etc.) together with the website.

In fact, since the ADI BF561 naturally has the characteristics of a symmetric multiprocessor (SMP) architecture, it uses two processors connected by a high-speed channel and shares peripherals and memory space [2], allowing developers to evenly distribute a large number of computing applications to each core, thereby maximizing the use of dual-core processor resources and effectively controlling costs. On the other hand, due to the programmable nature of DSP, in addition to being able to fully utilize processor resources, this system also has significant advantages in the subsequent expansion of multiple decoding capabilities (such as AVS).

In conclusion, this paper proposes and designs a broadband information terminal based on DSP, combining the current trend of "3C" integration and the current status of IPTV technology development. The terminal has high reliability, good scalability and excellent performance-price ratio, and has been effectively verified in the market mass promotion.