Abstract: Introduces the software and hardware architecture of the open multimedia platform provided by the US TI company, combined with the characteristics of the mobile multimedia communication terminal dual-core processor OMAP1510, elaborated the typical application of OMAP1510 in the third generation mobile communication network and related protocol analysis.
The third generation (3G) wireless communication technology will provide true broadband services for cellular communication systems and personal communication systems. Service providers will provide higher-level wireless multimedia services, including data, audio, video, and voice services. In order to fully tap the multimedia communication potential of 3G, system developers need a new type of software and hardware technology. Compared with the current situation, the hardware platform must have the characteristics of high performance, low power consumption, and high integration. Because it must comply with standards such as multimedia, mobile operating systems, and end users, and must also comply with a wide range of changes, programming must have greater flexibility.
The development of mobile communication puts higher and higher requirements on digital signal processors, and traditional DSP chips are no longer competent. In order to meet the needs of new applications in the field of mobile communications and multimedia, Texas Instruments has proposed an open multimedia application platform OMAP (Open MulTImedia ApplicaTIons Platform) architecture, and designed an OMAP chip for this. It adopts a unique dual-core structure, combining a high-performance low-power DSP core and an ARM microprocessor with strong control performance to become a highly integrated SoC. It is an open, programmable DSP-based architecture. Due to OMAP's advanced and unique structure, its chip has strong computing power and low power consumption, and it has obvious advantages in mobile communication and multimedia signal processing.
The mobile communication market continues to grow, and more and more wireless Internet applications are used. Separate terminals are gradually merged into a single multimedia terminal device. New applications, including MPEG4, TTS, Internet audio, and video conferencing, require more powerful processors with lower power consumption. OMAP chips fully meet the requirements of these new applications. In addition, OMAP's open architecture makes it easy for third-party developers to develop new wireless multimedia applications. OMAP's technical advantages in mobile communications and multimedia signal processing make OMAP chips very suitable for third-generation mobile phones, wireless digital assistants, future handheld computers and other fields.
TI currently offers a variety of OMAP platforms, including the OMAP1510 dual-core architecture processor. OMAP1510 provides an excellent platform for the development of 3G multimedia wireless devices.
1 OMAP1510 hardware architecture
The hardware architecture of OMAP is mainly composed of DSP core, ARM core and traffic controller. These three parts can independently manage the clock and effectively control power consumption, as shown in Figure 1. TI's enhanced ARM925 core is an advanced representative of the ARM RISC architecture, operating at a frequency of 175MHz. It includes a memory management unit, a 16K-byte high-speed instruction buffer memory, an 8K-byte data cache memory, and a 17-word write buffer. There is 1.5MB of internal SRAM in the chip, which provides a large amount of data and code storage space for applications such as liquid crystal display. It has 13 internal interrupts and 19 external interrupts, using two-level interrupt management. In addition, there are ARM CP15 coprocessor and protection module in the core. C55x DSP core has the best power consumption performance ratio, and the main frequency is 200MHz. It uses three key innovations: increased idle power-saving areas, variable-length instructions, and expanded parallelism. Its structure is highly optimized for multimedia applications and suitable for real-time voice and image processing with low power consumption. The C55xDSP core adds hardware accelerators that handle motion estimation, discrete cosine transform, inverse discrete cosine transform, and 1/2 pixel interpolation, reducing the power consumption of video processing. The C55x DSP core has 32K words of dual-access SRAM, 48K words of single-access SRAM, and 12K words of high-speed instruction cache. In addition, the core also contains a memory management unit, a two-level interrupt manager and a direct memory access unit. OMAPl510 chip has a wealth of peripheral interfaces, such as: LCD controller, memory, camera, air, Bluetooth, universal asynchronous transceiver, I2C host, pulse width audio generator, serial, host client USB, secure digital multimedia card controller , Keyboard and other interfaces. These rich peripheral interfaces make OMAP1510 especially suitable for the third generation mobile communication system.
2 OMAP1510 software architecture
The software structure of OMAP is built on two operating systems: one is an operating system based on ARM, such as Windows CE, Linux, etc .; the other is a DSP / BIOS based on DSP. The core technology used to connect the two operating systems is the DSP / BIOS bridge. It is the key to implementing and using OMAP. For software developers, the DSP / BIOS bridge provides a seamless interface using DSP, allowing developers to use standard application programming interfaces on GPP (General Purpose Processors, including ARM) to access and control the operating environment of the DSP. Using TI's Code Composer Studio integrated development environment, from a developer's perspective, OMAP seems to have completed all processing functions using only the GPP processor. In this way, developers do not need to program the two processors separately, which greatly simplifies programming. Under the OMAP architecture, developers can program OMAP's dual processor platform like a single GPP.
OMAP1510 supports a variety of real-time multitasking operating systems working on the ARM925 microprocessor. It is used for real-time multitasking scheduling management of the ARM925 microprocessor, controlling and communicating with the DSP C55x. Work on DSP C55x to realize complex multimedia signal processing. The DSP / BIOS bridge contains the DSP manager, DSP management server, RAM, DSP and peripheral interface link drivers. The DSP / BIOS bridge provides communication management services between applications running on ARM925 and algorithms running on DSP C55x. Developers can use the application programming interface in the bridge to control the execution of real-time tasks in the DSP and exchange task execution results and status messages with the DSP. In this environment, developers can call local DSP gateway components to complete functions such as video, audio, and voice. Therefore, developers do not need to understand the DSP and the bridge to develop new application software, as shown in Figure 2.
When developing multimedia applications, you can use the multimedia engine through the standard multimedia application programming interface (MM API) to facilitate the development of application programs; the multimedia engine uses DSP / BIOS through the DSP application programming interface (DSP APl) for related DSP tasks Bridge; Finally, the DSP / BIOS bridge coordinates the data, I / O flow, and DSP task control. As shown in Figure 3.
3 Dual-core communication
The software platform of OMAP is independent of the hardware platform. How to make the two operating systems work seamlessly is the key to realize an open software platform. Its core technology is to formally apply the DSP / BIOS bridge on the OMAP platform.
The DSP / BIOS bridge is used to connect the DSP and the OS on other general-purpose processors (GPP). GPP is ARM in OMAP, but also MIPS (Microprocessor without Interlocked Pipe Stage). The DSP / BIOS bridge is used in an asymmetric multiprocessor environment consisting of a general-purpose processor (GPP) and one or more DSPs. As a software combination of GPP OS and DSP OS, the DSP / BIOS bridge connects the two operating systems together. This connection enables customers on the GPP side to exchange information and data with tasks on the DSP. There are two types of connections: message sub-connections and data flow sub-connections. Each seed connection delivers messages in order, which message arrives first in the message chain, and which message is delivered first; similarly, which data stream arrives first in the data stream chain and which data stream is delivered first. Each sub-connection operates independently, for example: GPP sends the data stream first, and then sends the message; if the message has a high priority, then the message arrives at the DSP before the data stream.
DSP tasks usually use message objects to convey control and status information, and data stream objects to deliver efficient real-time data streams. Figure 4 shows the relationship between the GPP client program and the DSP task.
4 Typical applications
4.1 Multimedia terminal hardware solution
The hardware structure of the 3G mobile multimedia terminal based on OMAP1510 is shown in Figure 5. Among them, the 3G mobile phone card realizes the air interface function based on the 3G wireless transmission technology (RTT) specification, including the radio frequency module and the baseband processing module, and the corresponding physical layer software. This solution uses CDMA2000 technical specifications. The interface between 3G mobile phone card and OMAP1510 can be realized through TI peripheral bus interface.
4.2 Protocol software design scheme based on CDMA2000
The realization of CDMA2000 is divided into two stages: CDMA 2000-1X and CDMA2000-3X. The former's data rate is 144kbps, the latter's mobile car users reach 144kbps, mobile walking users can reach 384kbps, indoor fixed users reach 2Mbps, wireless Internet access, conference TV and other high-speed multimedia packet data services and voice services. The following mainly introduces the protocol software structure of the mobile multimedia terminal.
The terminal protocol structure consists of two parts: the signaling protocol stack and the application service protocol stack. The protocol software structure of the 3G mobile multimedia terminal based on CDMA2000 is shown in Figure 6.
The signaling protocol stack of CDMA2000 includes a high-level signaling layer, a data link layer (divided into LAC sublayer and MAC sublayer) and a physical layer. The high-level signaling layer mainly describes the signaling structure, security authentication, signaling control and application, message format, etc .; the LAC sub-layer provides reliability assurance of signaling transmission, including authentication, ARQ, function, split and reinstall, etc .; The MAC sublayer performs functions such as multiple tapping of logical channel services and QoS control; the physical layer implements the processing of physical channels such as data encoding, decoding, and modulation and demodulation.
The application service protocol stack includes multimedia video / audio codec, real-time transmission protocol (RTP), call control signaling protocol, TCP / IP, PPP, etc. The multimedia application in the 3G mobile communication system is based on IP packet data exchange, and the call control management of the multimedia session is completed by a set of signaling protocol sets. There are two commonly used: H. 323 (packet-based multimedia communication system) and SIP (session initiation protocol). H. given in Figure 6. 323 is currently a widely used signaling protocol set, in which the video codec uses H. 263 standard, audio codec uses G. 723 standard. RTP and its pairing protocol RTCP provide peer multimedia application layer related information, while UDP protocol can reduce the transmission delay of real-time multimedia streams. H. 225.0 and H. 245 agreements are H. The call control protocol of 323 runs on the TCP protocol.
Another important component of mobile multimedia terminal software is the embedded operating system. Currently popular popular embedded operating systems are VxWorks, WinCE, Linux, etc. Among them, Linux is open source code, low cost and high development potential, and supports ARM, PowerPC, x86 and other processors. Therefore, this solution uses an embedded Linux operating system. The embedded Linux operating system can be developed independently, or commercial mature products such as Î¼C Linux can be purchased.
Mobile multimedia business is the main feature of the third generation mobile communication system, so to develop 3G mobile terminals with multimedia functions, it is key to choose a good platform. OMAP1510 is designed with open software architecture and dual CPU hardware channels. For developers, it is easy to program and integrate. With the formation and maturity of the 3G service market in the future, the demand for 3G mobile multimedia terminals is believed to be increasing. This article discusses the implementation scheme of 3G mobile multimedia terminal based on OMAP1510 in combination with CDMA2000, which is one of the technical specifications of 3G wireless transmission. The terminal implementation scheme has been verified by relevant scientific research projects and has high feasibility.
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