Design of digital in-vehicle communication system

In recent years, with the continuous development of communication technology, microelectronics technology and computer network technology, the in-vehicle communication system is developing towards integration, digitization, networking and multifunctionality. The new generation of in-vehicle communication system should be able to realize unified voice exchange and processing inside, outside and between vehicles, meet the requirements of voice command and data sharing between passengers in the vehicle, and meet the requirements of direct voice command, voice dialing and data command between vehicles.

1 Overall framework design of in-vehicle communication system

The design idea of ​​the in-vehicle communication system is guided by advanced engineering design ideas and is designed using the most popular embedded development technology, computer network technology, digital communication and other advanced technologies to create a new type of digital in-vehicle communication system.

The communication modules of all the communication devices in the communication system adopt full-duplex switching Gigabit Ethernet switching modules, providing multiple 10/100 adaptive Ethernet interfaces. The communication devices are connected by switching port cascade, and the communication rate is 100 Mbps. The on-board computer or portable computer can be connected to any Ethernet port (ETH) of the communication device. The analog audio signal generated by the microphone is sampled and quantized into a digital signal and then transmitted through the system network. The voice signal is dynamically noise-reduced and amplified before being digitized.

2. Hardware Design of In-Vehicle Communication System

2.1 Hardware System Design

All devices in the in-vehicle communication system are uniformly developed using the ARM development platform and are interconnected through the Ethernet bus. The ARM processor mainly completes the input and output control of various switches, knobs, display screens and indicator lights, voice collection and playback, exchange and transmission processing, and network communication control. The system hardware block diagram is shown in Figure 2.

2.2 ARM main control board hardware design

The ARM main control chip is the latest 32-bit high-performance, low-power S3C6410 general-purpose microprocessor from SAMSUNG. The processor's external memory interface can meet the data bandwidth requirements in high-end communication services. In order to reduce the cost of the entire system and improve the overall function, the processor also includes many hardware functional peripherals, such as system management unit, 4-channel UART, 32-channel DMA, 4-channel timer, general-purpose I/O port, I2S bus, I2C bus, USB Host, high-speed USB OTC, SD Host, high-speed MMC card interface and internal PLL clock generator.

The ARM processor main control board hardware uses the AC97 interface to connect to the audio processing chip WM9714 to achieve voice collection and playback control. The ARM processor main control board converts the serial port TTL level into RS232 level through the SP3232 chip to achieve serial communication; through the FE1.1S chip to expand 4 USB Host interfaces, support USB devices such as U disk, mouse, keyboard, Bluetooth, etc.; through the Ethernet control chip DM9000AE to achieve network data transmission and control; through the I/O port to directly connect with display screens, rotary switches and indicator lights and other devices.

2.3 Audio Processing Module Design

The audio processing module uses the WM9714 chip, which is a highly integrated input/output device designed for mobile terminals and communications. It uses a dual codec operation architecture, supports high-fidelity (Hi-Fi) stereo codec functions through an AC connection interface, and also supports sound codec functions through a PCM-type synchronous serial port (SSP). The chip can be directly connected to mono or stereo microphones, stereo headphones, and stereo speakers, thereby reducing the total number of system components. Capacitor-free connections with headphones, speakers, and receivers can save costs and printed circuit board area.

The ARM processor can connect and control all chip functions through a separate AC-Link interface that complies with the AC-97 standard. The WM9714 chip can directly input a 24.576 MHz master clock, or the on-board phase-locked loop can generate it internally from a 13 MHz (or other frequency) clock. The WM9714L operates with a power supply voltage range of 1.8 V to 3.6 V; any part of the chip can be shut down through software control to reduce power consumption.

2.4 Network control module design

The system network control uses DAVICOM's DM9000AE chip, which integrates 10/100M transceiver, 4K double-word SRAM, supports 8/16-bit working mode, cross line adaptive function, MII/RMII interface and UDP/TCP/IP acceleration. The chip can be connected to the microprocessor in 8-bit or 16-bit bus mode, and can run in simplex or full-duplex mode as needed. The network interface uses the HR911105A chip, which has the advantages of signal coupling, electrical isolation, impedance matching, and interference suppression. Since the HR911105A comes with a network transformer, the DM9000AE receiving signal lines RX+, RX- and the sending signal lines TX+, TX- can be directly connected to the sending and receiving pins of the HR911105A. The main function of the network transformer is to isolate the embedded system from the external line, prevent interference and burn out components, and realize the plug-in and pull-out function with power on.

3. In-vehicle communication system software design

3.1 Embedded operating system selection

The embedded operating system uses WinCE (Microsoft Windows CE) system as the operating system for ARM processors. The main reasons are as follows.

(1) Widespread use of Microsoft Win32 application programming interface (API);

(2) WinCE is a compact, efficient and scalable 32-bit embedded operating system;

(3) The WinCE system is powerful and can complete most of the functions of a PC. It provides a friendly human-computer interaction interface and can use tools such as mouse and keyboard;

(4) The kernel can be tailored according to application needs, reducing system overhead, improving stability, and shortening startup time;

(5) WinCE is a strict real-time operating system.

3.2 Embedded Programming

The ARM embedded program adopts object-oriented and modular programming ideas. According to the functions, the entire program is divided into key input module, panel display module, parameter configuration module, network transmission control module, voice collection and playback module and program upgrade module. Its composition is shown in Figure 3.

Corresponding to the above 6 modules, the entire embedded program adopts object-oriented programming method, and the functional modules are implemented by 6 classes respectively. Its functions are shown in Table 1. Among them, the network transmission control module uses TCP/IP, RTP/RTCP/UDP protocols to realize the transmission of voice data and signaling. The voice data format adopts PCM encoding, mono, 11025 Hz sampling rate, and 8 bit data width.

4 Conclusion

In recent years, the in-vehicle communication system has developed rapidly with the development of digital communication technology, network technology and microelectronics technology. It has developed from the analog exchange mode to the fully digital and networked stage. The new in-vehicle communication system adopts a large number of modern electronic technologies, with high integration and networking, and convenient and reliable interconnection between in-vehicle equipment and between vehicles. The in-vehicle communication system solution designed in this paper is based on the ARM embedded system, and makes extensive use of modern microelectronics design technology, IP technology, etc., making the entire system highly integrated and networked. Therefore, the solution designed in this paper has certain reference significance for engineering research and development.