1 Introduction
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At the end of the 20th century, the wave of information revolutions that have arisen around the world has provided a rare opportunity for the breakthrough development of the automotive industry. The widespread application of information technology is to solve problems such as traffic congestion, traffic safety, environmental pollution, and energy depletion brought by automobiles. The best way. At the same time, with the development of automotive electronics technology, the proportion of electronic components in the overall vehicle cost has gradually increased. According to statistics, at present, electronic components in automobiles produced in Europe and the United States account for 20% to 30% of the total cost of automobiles, and automotive electronic components are also growing at an annual rate of 8.8%, especially digital signals. The amount of processor chips (DSP) will increase by 25% per year. It is estimated that by 2005, the market size of automotive electronic components will reach 17 billion US dollars. It can be seen that electronicization, integration, digitization, informationization, networking, intelligence, miniaturization and personalization have become and will continue to be an important trend in the development of the automotive industry. This article focuses only on digital applications based on DSP and FPGA in automotive electronics.
DSP and FPGA technologies are widely used in many fields, and they have a wide application stage in the field of automotive electronics. Due to its strong real-time nature, it is possible to make its voice processing real-time. Because it implements its functions through software programming for chip structure instructions, it can improve the system original only by modifying the software without changing the hardware platform. There are design schemes or original functions, which have great flexibility; and because DSP and FPGA chips are not designed for a certain function, they have a wide range of uses, large output, and low price. Therefore, DSP and FPGA are widely used in automotive electronic systems, which will greatly promote the development of automotive electronic technology.
2 Comparison of DSP and FPGA in automotive electronics
As a programmable very large scale integrated circuit (VLSI) device, DSP implements extended algorithm and digital signal processing functions through downloadable software or firmware. The most typical use is to implement FIR filter and FFT algorithm. In hardware, the most basic building block of a DSP is a multiplier called MAC, which is usually integrated into the data channel, which allows the instruction cycle time to be the same as the hardware's arithmetic cycle time. In addition, the DSP chip has several independent on-chip memories, ROM, RAM, parallel function units, phase-locked loops (PLLs), oscillators, several 8-bit or 16-bit buses, clock interrupt circuits, and so on. In order to meet the requirements of wireless portable devices to save data without electricity, DSP chips also use technologies such as flash memory and ferroelectric memory. At present, most DSP chips adopt a modified Harvard structure, that is, the data bus and the address bus are separated from each other, so that processing instructions and data can be simultaneously performed, thereby improving processing efficiency. In addition, the pipeline technology is adopted, and the instruction time of the steps of taking fingers, taking operands, and pointing fingers can be overlapped, and the operation speed is greatly increased.
The FPGA refers to the field programmable gate array. Its basic functional modules are composed of a n-input lookup table, a data storage trigger and a repeater. Thus, as long as the data therein is correctly set, the lookup table can implement an arbitrary Boolean function of the input by reading the data in the alignment. The trigger is used to store data, such as status information of a finite state machine. The combiner can select different combinations of input signals, and connect the lookup table and flip-flops with programmable routing resources to implement different combinational logic and timing logic. Due to the internal structure of the FPGA, it can easily implement a distributed algorithm structure, which is very beneficial for high-speed digital signal processing in automotive electronics. Since the functional blocks implemented by the FPGA device can work simultaneously, the parallel execution of the instruction level, the bit level, the pipeline level, and even the task level is realized, thereby greatly speeding up the calculation. The computing system implemented by FPGA can reach hundreds or even thousands of times of existing general-purpose processors. Also, since the FPGA can be dynamically configured, the silicon area of ​​the system is no longer a linear function of the number of supported wireless interfaces, so it is possible to integrate a system that supports all standards in a few pieces or even a single FPGA. However, since the existing FPGA development systems are almost all designed for ASIC prototyping, these development systems are very efficient in saving engineering development time, but in terms of FPGA resource utilization efficiency. The HDL language can greatly improve the design capability, but the HDL design method has certain limitations in maximizing device performance, and it cannot provide optimization and constraints for FPGA layout.
3 DSP and FPGA applications in automotive electronics
When it comes to the digitization of automotive electronics, you can't think of the software radio technology that wireless communication is very promising. Although it is aimed at wireless communication, the idea of ​​software radio and the goal of digitalization of automotive electronics are The same road is the same. Therefore, it is necessary to mention and adopt the implementation ideas and ideas of this technology. The software radio concept was first explicitly proposed in May 1992 by Joe Mitola of MITRE Corporation, which is the product of today's computing technology, VLSI and digital signal processing technology in wireless communications; the basics it pursues The idea and goal is to construct a universal hardware platform with openness, standardization and modularization, and implement various functions such as working frequency band, modulation and demodulation type, data format, encryption mode, communication protocol, etc. in software to achieve A highly flexible, open communication product. Therefore, the research on automotive electronic digital products can fully absorb the following main ideas of software radio: first, to get rid of the shackles of hardware and electronic products; second, not to avoid hardware; third, automotive electronics products should have Openness and compatibility, openness refers to openness to use, openness to production, and openness to development. Below, we will discuss the main applications of DSP and FPGA in automotive electronics based on the idea of ​​software radio.
3.1 Based on DSP and FPGA for vehicle voice signal processing
Speech processing in automotive electronics mainly involves digital processing of speech, speech encoding and decoding, speech compression and speech recognition. One of the more popular automotive electronic products in foreign countries is the speech recognition system. The speech recognition system has potential application prospects, including voice-activated telephone, voice operation navigation, voice-activated selection of broadcast channels, and anti-theft voice identification. For example, an application based on the implicit Markov model (HMM) that is independent of the speaker and 100 instructions, as the literature knows, the size of the acoustic HMM model will be. Timely processing such as subdivision/windowing, MFCC extraction, probability calculation, and Viterbi search including input speech sampling is performed, and the calculation amount of the DSP is generally 100 million times multiplication plus (MAC) operation. For the recognition of continuous speech signals, better digital signal processing speed and greater storage space are required.
Since the speech recognition system needs to process and sample the sound in real time, a large amount of operations are required. If 20% of the computing resources are allocated for 10 million MAC speech recognition applications, the processor needs to have the capability of 50 million MAC addresses. Therefore, DSP and FPGA must be used to complete their tasks. The processing speed of DSP and FPGA plays a decisive role in the complexity and performance of speech signal processing applications. High-speed DSP and FPGA implementation can realize modern speech processing and recognition technologies such as channel adaptation and sound domain adaptation. In theory, the faster the processing speed of DSP and FPGA, the better the application performance of automotive speech processing and recognition products.
As applications become more diverse, DSPs and FPGAs evolve into devices that are no longer a separate chip. This allows designers to choose the right core and dedicated logic to "glue" together to form a dedicated DSP and FPGA solution to meet the needs of signal processing. Currently, there are also chips that integrate DSP cores and ASIC microcontrollers. Automotive electronic systems use general purpose DSPs and FPGAs to implement speech synthesis and error correction coding. Speech synthesis, speech compression and coding are the earliest and most widely used applications of DSP. Vector encoders are used to compress speech signals into channels of limited bandwidth.
3.2 Vehicle image signal processing based on DSP and FPGA
Digital image processing and analysis technology is a relatively mature two-dimensional signal processing technology, which has been widely used in communication, biomedical, industrial inspection and military, and of course, a large number of images will be involved in automotive electronics. Processing. Image processing in automotive electronics mainly includes moving image processing and still image processing. At present, vehicles in many industries have already opened the Global Positioning System (GPS). In addition to transmitting its own position coordinate information, the on-board GPS system also needs to transmit image information of its environment, such as the scene of the rescued casualty and the image of the emergency relief scene. At the same time, the traffic monitoring image of each traffic intersection should be transmitted back to the traffic command center, and the image signal processing is also required. For this kind of car moving image, the main features are: First, multi-rate compression. Due to the time-varying nature of the wireless channel, the effective bandwidth, transmission mode, and data rate of the system tend to change constantly; accordingly, multi-rate compression is needed to flexibly adapt to this change in channel bandwidth. Second, the compression ratio is large. For example, the data volume of NTSC TV images is about 167Mb/s, and it needs to be compressed by 200 to 6000 times to meet the requirements of transmission bandwidth. Third, motion compensation of moving images. The moving image has a Doppler shift problem due to its relative motion. For high-speed sports cars, this frequency shift is often not negligible and motion compensation must be performed on the acquired image.
In recent years, with the rapid development of microelectronics technology and the improvement of chip manufacturing technology, DSPs and FPGAs have emerged. The signal processing system of a previous chassis and even a cabinet can now be completely completed by a single DSP or FPGA. The system design will also transition from the past PCB board design to the design of VLSI and UVLSI (very large scale integrated circuit) chips. At the same time, due to the large number of DSP and FPGA technologies, digital image processing has undergone major changes in hardware architecture. It has evolved from a basic serial structure to a parallel processing structure, which is developed from a single DSP or FPGA processor. Multi-DSP or FPGA processor systems, or high-speed processing systems with array DSPs and FPGAs. With the development of society and economy, and the real-time requirements of digital image processing systems, the application of digital image processing systems based on DSP and FPGA will become more and more widely used in automotive electronics. Car conference TV, car videophone, car machine vision, etc.
3.3 Vehicle adaptive real-time processing based on DSP and FPGA
The clock delay of the FPGA can reach nanoseconds, combined with the parallel processing of DSP and FPGA, so DSP and FPGA are very suitable for ultra-high speed and real-time signal processing. As mentioned earlier, due to the internal structure of the FPGA, it can easily implement a distributed algorithm structure, which is very beneficial for high-speed digital signal processing in automotive electronics. Because automotive electronics generally require a large number of filtering operations, these filtering functions often require a large number of multiply and accumulate operations, and through a distributed arithmetic structure, the FPGA can effectively achieve multiply and accumulate operations. On the other hand, a large amount of complex mathematical operations are required, which can be done by means of a DSP or an ASIC composed of DSP cores. In automotive electronics, special attention is paid to the size, weight, and power consumption of products; in data transmission, large amounts of data generated by digitizing audio signals in automotive electronic systems rely on high-performance DSPs and FPGAs to reduce storage space. And the transmission bandwidth requirements, the video signal and audio signal encoding, decoding, color space conversion, echo cancellation, filtering, error correction, multiplexing, bit stream protocol processing and other tasks need adaptive real-time processing, which is often non- DSP and FPGA cannot be completed.
Control theory processing is a difficult and important problem in automotive electronics. The open-loop, infinite loop, optimal and adaptive control systems established by classical and modern control theory are used to achieve optimal control of automobiles. The establishment of these control systems first identifies a certain vehicle system, such as the ignition advance angle optimization control system, establishes a mathematical model of the system, and then uses the corresponding control method for optimal control. However, the structure of the engine itself is more complicated, and there are many factors affecting the ignition. It is difficult to theoretically derive the mathematical model under the optimized ignition state. Therefore, the experimental method is generally used to find the optimal ignition advance angle under various operating conditions, and then stored in the external memory based on DSP and FPGA or DSP and FPGA array to increase the capacity; this can avoid the use of computers. In the control process, the system detects the operating conditions of the engine (such as engine speed, power, etc.) in real time, and uses the method of look-up table to find the optimal ignition advance angle under the working condition, and then corrects the ignition before controlling. This is much less than the traditional computer-based control method, on the one hand, the volume is greatly reduced; on the other hand, it is more real-time and flexible. Suspension electronic control refers to the control system that can adaptively handle the roll and forward and backward of the vehicle and automatically adjust the damping force of the shock absorber after the computer detects the signals of the steering and braking conditions, which can prevent the tilt and improve The ground adhesion of the wheel, the ultrasonic height sensor is used to control the height of the vehicle body, the air spring is used to adjust the elastic system, the grating detector is used to measure the steering angle and the like. The emergence and development of DSP and FPGA have led to the centralized control of each system to form an intelligent control system for the entire vehicle.
"Intelligent Transportation System" will be the common pursuit of the future automotive and transportation industry, and it will include intelligent highways and smart car systems. It combines advanced highway information processing technology and radar anti-collision technology to connect roads and automobiles as a whole, which can greatly improve vehicle traffic and greatly reduce the incidence of traffic accidents. Therefore, automotive-related products have been highly valued by automakers. The intelligent transportation system can provide the driver with the shortest distance according to the target data provided by the driver, and can bypass the optimal driving route where the vehicle density is relatively concentrated. "Safety first" is always the first choice for users to buy a car. At present, the research on the relatively hot millimeter wave adaptive anti-collision radar for vehicles is developed to solve a large number of traffic accidents caused by crashes on the expressway. Since the relative speed between the highway cars is very high, the extraction of the frequency difference of the radar echo signals must be in real time. Therefore, for the extraction and processing of the radar echo signal frequency difference, and the feedback control processing of the adaptive anti-collision control system, it is often implemented by DSP or FPGA.
4 Development prospects
Throughout the major achievements of automotive technology in recent decades, most of them have made breakthroughs in the application of electronic technology, and electronic technology has become an important source of power for the development of the automotive industry. The advent of DSPs and FPGAs has revolutionized automotive and automotive electronics. The world's automotive industry has seen a surge in DSP and FPGA usage. It has evolved from a single DSP or FPGA processor to a multi-DSP or FPGA processor, or DSP. And high speed processors for FPGA arrays. Automotive electronics based on DSP and FPGA can meet the needs of future automotive development, and in the era of multiple models coexisting, the general hardware platform built with DSP and FPGA as the core can be loaded by different software. To achieve this compatibility. With the continuous development of automotive electronics technology in the future, the speed of DSP and FPGA will continue to increase. As far as DSP is concerned, it is developing very fast. The main trends are: implementing multiple MACs, more registers, wider program bus and data bus, and higher operating frequency in a single DSP; SIMD and MIMD use super long instructions. As far as FPGAs are concerned, due to the adoption of sub-micron processes, they are faster and have more gates. At present, Lucent and XILINX have more than 100,000 products and integrate some new functions, such as System on Chip, Programming on System, etc., to make it more flexible.
China's research on automotive electronic systems is not deep enough. Automobile brake anti-lock braking systems, airbags, automatic transmissions and diesel electrical control systems have only been explored in some universities and enterprises, and have not entered the practical stage. High-tech, represented by automotive electronics technology, is the "bottleneck" in the development of China's automobile industry. In view of this situation, the research of China's automotive electronics technology should focus not only on the energy conservation, environmental protection and safety of automobiles, but also strive to master their core technologies as soon as possible, narrow the gap with developed countries, and more should be based on vehicle communication and high-speed real-time signal processing technology. This kind of emerging technology is a breakthrough, relying on the results of national information technology research, developing advanced in-vehicle computing and information processing products, driving the advancement of the entire automotive electronics technology and improving the electronic level of China's automobiles.
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