Abstract: With the rapid development of the domestic automotive electronics industry, car navigation systems and MOST network transmission systems have become two hotspots in the automotive electronics industry today. The combination of the navigation system and the MOST network enables the traditional GPS navigator to not only increase the streaming media playback function, but also reduce the car wiring and increase the anti-electromagnetic interference and scalability of the product. Research on car navigation system and MOST network, improve the traditional car navigation system, and give the design. Due to the low power consumption of the AUl200 and MOST network design, the system's performance, integration and scalability are improved, and the system is characterized by high functionality, low power consumption and high reliability.
Keywords: MOST; I2S; multimedia; GPS
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Based on MOST (Media Oriented Systems Transport), automotive optical fiber transmission multimedia has become the mainstream of automotive multimedia. This technology has been popularized in cars abroad, and digital multimedia devices are regulated. Transmission using MOST optical network is not affected by electromagnetic interference, and bus wiring is also reduced. With the development of automotive optical network technology, more and more automobile manufacturers will support the MOST protocol. Therefore, it is predicted that domestic automotive optical fiber transmission multimedia audio-visual products will also have a wide market.
1 Introduction to AUl200 In January 2005, AMD introduced the processor AUl200 specifically designed for multimedia. It supports NORFLASH, NAND FLASH boot, supports DDR I and DDR II SDRAM, supports RGB LCD display, supports I2S, USB 2.0, SD card and other functions. It is a high performance and low power MIPS multimedia processing chip. Support WINCE, Linux operating system.
2 system working principle and chip selection The system uses Hynix's HY5DUl21622BT-D4364 MB DDRI memory, Samsung K9F1208UOB 64 MB NAND FLASH, Foxconn Group 7 inch LCD AT070TN83, top international
REB3310 GPS module, UART debug output interface is left on the board for easy debugging.
The system is started by FLASH, and the program is copied to the memory to run. The user can select the function to be run through the touch screen, such as GPS, play MP3, MP4, or select to receive and process audio data from the MOST network. In the debugging process, the debugging information can be output to the PC through the reserved DEBUG port external LVTTL to RS 232 level conversion chip, and the programming program can be upgraded through USB. The SD card can store electronic maps, audio and video files or other electronic files. The software uses WINCE operating system, WINCE with AUl200 BSP driver package, easy to cut. The block diagram of the system working principle is shown in Figure 1.
2.1 I2S audio design and its part of the workflow I2S chip selects the WM9713L chip. The main function of the chip is to convert the audio data transmitted by AUl200 and OS8104 into D/A conversion and become the analog audio signal output. WM-9713L chip can realize two-way I2S audio data input, support AC97 audio data and PCM I2S audio data input interface, which can easily realize AUl200 and WM9713L, OS8104 and WM9713. At the same time, WM9713L PCM/I2S function module can work in four working modes: DSP mode, left channel mode, right channel mode and I2S mode. The signal-to-noise ratio is 94 dB when D/A, and it supports WINCE embedded operating system. The WM9713L also drives a four-wire touch screen.
The power amplifier uses Supec's BTL class SA4871 amplifier. The power amplifier works in the voltage range of DC 2.5 ~ 5.5 V, can be directly powered by a lithium battery, output 3 W power.
The WM9713L comes with a BTL amplifier. Since the WM9713L has an output power of only 400 mW, the SA4871 has an output power of 3 W. Considering the user's requirement for volume, the SA4871 is selected.
When playing multimedia files such as MP3 and MP4, the sound can be sent to the WM9713L for D/A conversion through the AUl200 I2S interface. If you need to play audio data transmitted through MOST fiber, you can set the WM9713L internal register 18H to make the audio data directly through the WM9713L for D/A output.
WM9713 and AUl200 OS8104 I2S data transmission wiring diagram shown in Figure 2.
2.2 0S8104 working mode Adopt OS8104 produced by OASIS company, its main function is to decompose the data on the optical network and output I2S audio data to WM9713L for decoding. Its control interface has multiple working modes, I2C, SPI, parallel port mode, etc. Here, I2C working mode is selected to configure the internal registers of OS8104.
The OS8104 I2S supports a variety of data source formats such as Philips, Sony, Matsushita, etc. Since the WM9713L supports the I2S PCM data format, by comparing the timing waveforms of both, Philips or MatslJshita is selected, and the WM9713L works in DSP mode. In order to receive the I2S data of the entire MOST system, the OS8104 register needs to be configured to set the sampling frequency of the I2S. The 44.1 kHz sampling frequency is used here. MOST data transfer uses 512 b frames, as well as blocks of 16 frames. In addition to preambles and other internal management bits, each frame contains synchronous, asynchronous, and control data. The source data port of the MOST network interface device is configured as I2S serial mode, and the maximum synchronous data transmission rate is: 
3 software interface development Using WINCE 5.0 embedded operating system, its characteristics are stable performance. EVC (Embedded Visual C++, one of the software development tools under Windows CE) develops a graphical interface, which is characterized by a beautiful interface. The EVC development environment is similar to Visual C++. Visual C++-based developers are more likely to be familiar with and master EVC for embedded application interface development. There are more electronic maps supporting WINCE operating systems, such as Kay LiDE and Dao Dao Tong.
WINCE migration needs to be tailored, first install WINCE 5.0 AUl200BSP driver package and then cut, and change some of the underlying drivers. The system startup process can be controlled by the computer RS ​​232 serial input button. The program flow chart is shown in Figure 3.
4 Test results and performance analysis AUl200 power consumption is less than 400 mW at 400 MHz main frequency. The AUl200 core of this system works at 396 MHz frequency when playing MP4 or navigation, DDR works at 198 MHz, and the whole machine consumes less power.
4 W (menu operation, no speakers). When playing MP3, reduce the system and DDR frequency, turn off the GPS module, and make MOST in zero power state mode to reduce power consumption. After testing, the power consumption can be reduced by 1.5 W. Play 1 kHz sampling rate is 44.1. The sine wave of kHz has a signal-to-noise ratio of 85 dB and has a good sound quality.
5 Conclusion The multimedia player, with low power consumption, high performance and versatility as the main goal, chooses the AUl200 as the main chip, optimizes the external circuit as much as possible, reduces power consumption, increases the service life and improves the user experience.
The novelty of the design: the combination of MOST network and multimedia GPS navigation realizes the switching of MOST audio and node streaming media audio; adopts WINCE operating system and has beautiful interface.
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