| In recent years, the rapid development of digitization technology centering on computer, chip technology and software engineering, greatly boost the research of embedded technology. Powerful embedded processor and excellent embedded operating system have been developed successively, which makes the application of embedded system more and more widespread and contain each aspect of national economic construction. Embedded operating system runs on embedded processor, it can dispatch all tasks, manage the processor and other hardware devices. Embedded operating system shields the bottom details and affords the unified programming interfaces for users. This method enhances the product development efficiency.With the development of embedded technology, the multimedia terminal with the function of multimedia process and network access could satisfy different need and have played leading role in the individual electronic consumables. At present trend, it will replace partly the PC machine and has been more and more popular in the market. With the rapid development of network, using PC to surf the Internet in the settled site can't satisfy people need, the wireless network become favourite, and the WiFi technology become more and more mature. The combine with the embedded and WiFi technology provide new chance for the future wireless embedded equipment.The large digitization multimedia data in the information period bring the huge challenge for embedded equipment with limited resource. The multimedia process based on embedded environment becomes more hot in research field. And the rapid development of wireless network made people access to internet in anywhere at any moment, the need for the portable terminal with the function of accessing to wireless network enhances gradually. The future trend for multimedia terminal is to support more media formats, more convenient network access and richer expanding functions. According to these requirements, the embedded wireless multimedia terminal platform based on XScale and Linux is designed and realized in this paper. This studying supplies the platform for developing the wireless multimedia equipment and different application like remote image surveillance system and embedded set-top box.According to the goal and request of design, the system must accomplish the complicated video and audio decoder, and manage a lot of hardware resource, so it need high-powered embedded processor, operating system to dispatch resource and application software to realized the function. The terminal platform in this thesis adopts Intel XScale PXA255 processor, Linux operating system and software decoder to support more media formats. This system support video decoder like MPEG-1, MPEG-2, MPEG-4, H.263 and audio decoder like MP3, WAV and etc. It also support to access to Ethernet and WiFi expediently through 802.11b protocol. The terminal platform design and realization mainly contain the following aspects:1. The hardware platform uses Intel XScale PXA255 processor, 32M bytes Flash memory, 64M bytes SDRAM to construct the core circuit system, with expanding audio codec CS4297A, Ethernet controller CS8900A, LCD PD064VT2, touch screen A/D ADS7843, IDE and PCMCIA interface to design hardware circuit and ultimately implement the hardware platform of the terminal. Intel XScale PXA255 is a high-powerful embedded ARM processor introduced by Intel Corporation. It supports virtual memory management with MMU, pipelining, cache and the highest working frequency can be up to 400MHz. CS4297A is an audio codec for multimedia system according with AC97 2.1 standard and used for audio recording and playing. CS8900A is a high-integrated Ethernet controller and used for network communication. PD064VT2 is an active TFT LCD, its size is 6.4 inch, used for display. ADS7843 is used to convert the analog signal to digital signal for fixing on the orientation of touch screen. IDE interface realizes high-capacity data storage. PCMCIA interface is used to connect WLAN card, and realize the access to wireless network.2. Drawing PCB board of 6 layers for terminal platform. In the design course, the layers sequence with signal, ground, power, signal, ground and signal. Considering the control for characteristic impedance when arranged the power and ground layers. Repartitioning the sub area according with function, and arranging components in every sub area. To avoid disturbing between digital signal and analog signal, the design of mixed signal sub area should be used. This method can detach the function modules to decrease the disturber of them. Considering the signal integrality and laying out lines with handwork. Summarizing some basic rules and attentive matters of drawing PCB board of 6 layers.3. U-Boot 1.1.4 is ported as boot loader adapting to this terminal platform. In debug phase, boot loader should support the serial and network in order to debug expediently and download image. Linux 2.6.14 is also ported to this terminal platform. According to hardware interface and time sequencing, design drivers of peripheral equipment based on actual hardware circuit and realize the management for peripheral interface. A file system with JFFS2 format is realized by using the Busybox.4. Port MiniGUI as the GUI of this terminal platform, analyze the structure and programming of MiniGUI, design the Interface Abstract Layer for this terminal platform to support touch screen and keypad. FFMPEG libraries are used to parse file format and decode audio and video data. Specially analyze the decoder of MPEG4 and optimize the program to the application on embedded system. SDL libraries are used to realize the playing program. A timer with cycle of 40ms is used in the main routine. A frame of video data and synchronized audio data are decoded and played when each event of the timer arrives, in addition the program could support the conversion among the media formats and some games. Through designing the driver of PCMCIA interface on terminal platform and supporting 802.11b protocol in the kernel, the terminal platform could access to WLAN.Through debugging and testing, the hardware and embedded Linux operating system run stably, the GUI is friendly and multimedia is played smoothly. The terminal platform also supports the conversion among the media formats, some games and access to Ethernet and WLAN. The terminal platform can be expanded both on software and hardware in order to be applied in more fields. It's believed that the combine with the embedded and wireless technology provide new direction for the future embedded equipment. |
PDF Full Text Request