Application of DSP and FPGA in automotive electronics
1 Introduction
At the end of the 20th century, the wave of the information revolution that has emerged around the world has provided a once-in-a-lifetime opportunity for the breakthrough development of the automotive industry. The wide application of information technology is to solve problems such as traffic congestion, traffic safety, environmental pollution, and energy depletion caused by automobiles The best way. At the same time, with the development of automotive electronic technology, the proportion of electronic components in the total vehicle cost has gradually increased. According to statistics, at present, electronic components have accounted for 20% to 30% of the total cost of automobiles in European and American countries, and automotive electronic components are also growing rapidly at a rate of 8.8% per year, especially digital signals The amount of processor chips (DSP) will grow at an annual rate of 25%. It is estimated that by 2005, the market size of automotive electronic components will reach 17 billion US dollars. This shows that electronic, integration, digitalization, 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 only focuses on the digital application technology based on DSP and FPGA in automotive electronics.
DSP and FPGA technology are widely used in many fields, and also in the field of automotive electronics. Because of its strong real-time performance, it is possible to process the voice in real time; because it realizes its functions through software programming oriented to chip structure instructions, it is possible to improve the original system by only 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 specifically designed for a certain function, they have a wide range of applications, large output, and low prices. Therefore, the large-scale application of DSP and FPGA in automotive electronic systems 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 algorithms and digital signal processing functions through downloadable software or firmware. Its most typical use is to implement FIR filters and FFT algorithms. On the hardware, the most basic building block of DSP is a multiplier called MAC, which is usually integrated in the data channel, which makes the instruction cycle time can be the same as the hardware arithmetic cycle time. In addition, the DSP chip has several independent on-chip memories, ROM, RAM, parallel functional units, phase-locked loops (PLL), oscillators, several 8-bit or 16-bit buses, and clock interrupt circuits. In order to meet the requirements of wireless portable devices to save data without electricity, DSP chips also adopt technologies such as flash memory and ferroelectric memory. At present, most DSP chips use an improved Harvard structure, that is, the data bus and the address bus are separated from each other, so that processing instructions and data can be performed simultaneously, improving processing efficiency. In addition, pipeline technology is used to overlap the instruction time of the steps of fetching instructions, fetching operands, and executing instructions, which greatly improves the speed of operation.
FPGA refers to the field programmable gate array, and its basic functional module is composed of a look-up table of n inputs, a trigger to store data, and a multiplexer. In this way, as long as the data in it is set correctly, the lookup table can realize any Boolean function of the input by reading the data in the. The trigger generator is used to store data, such as the state information of the finite state machine. The multiplexer can select different combinations of input signals, connect the lookup table and the trigger with programmable wiring resources, and can realize different combinational logic and sequential logic. Due to the characteristics of the internal structure of FPGA, it can easily implement a distributed algorithm structure, which is very beneficial to the realization of high-speed digital signal processing in automotive electronics. Because the function blocks realized 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 speed. The computing system implemented by FPGA can reach hundreds or even thousands of times of the existing general-purpose processors. And because FPGA can be dynamically configured, the silicon area of ​​the system is no longer a linear function of the number of wireless interfaces supported, so it is possible to integrate a system that supports all standards in a few or even a single FPGA. However, because almost all existing FPGA development systems are designed for ASIC prototyping, these development systems are very efficient in saving engineering development time, but are relatively poor in FPGA resource utilization efficiency. HDL language can greatly improve the design capabilities, but HDL design methods have certain limitations in maximizing the performance of the device, and they cannot provide optimization and constraints for FPGA placement and routing.
3 DSP and FPGA applications in automotive electronics
When it comes to the digitization of automotive electronics, one cannot think of the current software radio technology that is very optimistic about wireless communication. Although it is aimed at wireless communication, the idea that software radio wants to achieve is the same as the goal pursued by digital processing in automotive electronics The same way. Therefore, it is necessary to mention and adopt the implementation ideas and ideas of this technology. The first clear introduction of the concept of software radio was in May 1992, proposed by Joe Mitola of MITRE. It is the product of the application of today's computing technology, VLSI and digital signal processing technology in wireless communication; the basic it seeks The idea and goal is to construct a general hardware platform with openness, standardization, and modularity, and implement multiple functions, such as working frequency band, modulation and demodulation type, data format, encryption mode, communication protocol, etc., with software to achieve A highly flexible and open communication product. Therefore, for the research of automotive electronic digital products, the following main ideas of software radio can be absorbed: first, to make automotive electronic products get rid of the constraints of the hardware structure; second, not to not need hardware; third, automotive electronic products should have Openness and compatibility, openness means openness to use, openness to production and openness to research and development. Next, based on the idea of ​​software radio, discuss the main applications of DSP and FPGA in automotive electronics.
3.1 Vehicle-based voice signal processing based on DSP and FPGA
Voice processing in automotive electronics mainly involves digital processing of voice, voice encoding and decoding, voice compression, and voice recognition. One of the more popular automotive electronic products abroad is the voice recognition system. The voice recognition system has potential application prospects, including voice-controlled telephones, voice-operated navigation, voice-controlled selection of broadcast channels, and anti-theft voice authentication. For example, an application based on the Hidden Markov Model (HMM), which has nothing to do with the speaker and recognizes 100 instructions. From the literature, the size of the acoustic HMM model will be. Carry out timely processing including subdivision / windowing of input speech samples, MFCC extraction, probability calculation, and Viterbi search. The computational requirements for DSP are generally 100 million multiply-add (MAC) operations. For the recognition of continuous speech signals, it requires better digital signal processing speed and larger storage space.
Since voice recognition systems need to process and sample sound in real time, a large amount of calculation is required. If 20% of their computing resources are allocated to 10 million MAC speech recognition applications, then the processor needs to have the capability of 50 million MACs. Therefore, DSP and FPGA must be used to complete its task. The processing speed of DSP and FPGA plays a decisive role in the complexity and performance of the voice signal processing application system. The realization of high-speed DSP and FPGA can realize modern voice processing and recognition technologies such as channel adaptation and sound domain adaptation. In theory, the faster the DSP and FPGA processing speed, the better the performance of automotive voice processing and recognition products.
With the increasing diversification of applications, DSPs and FPGAs have evolved from being independent chips to component cores. This allows designers to select the appropriate core and dedicated logic to "glue" together to form a dedicated DSP and FPGA solution to meet the needs of signal processing. At present, there are also chips that integrate DSP cores and ASIC microcontrollers. Automotive electronic systems use general-purpose DSP and FPGA to achieve speech synthesis and error correction coding. Speech synthesis, speech compression and coding are the earliest and most widely used DSPs. Vector encoders are used to compress speech signals into channels with 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 communications, biomedicine, industrial detection and military, etc. Of course, a large number of images will also be involved in automotive electronics Handling. Image processing in automotive electronics mainly includes moving image processing and still image processing. At present, the global positioning system (GPS) has been opened in many industries. In addition to transmitting its own position and coordinate information, the vehicle-mounted GPS system also needs to transmit image information of the environment in which it is located, such as the scene picture of the rescued wounded and the image of the emergency disaster relief scene. At the same time, the flow monitoring images of each traffic intersection need to be transmitted to the traffic command center, and 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 wireless channels, the effective bandwidth, transmission mode, and data rate of the system are constantly changing; accordingly, multi-rate compression is required 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 must be compressed by about 200 to 6000 times to meet the requirements of transmission bandwidth. Third, motion compensation of moving images. Due to its relative motion, the moving image will have Doppler shift problem. For high-speed moving cars, this frequency shift is often not negligible, and motion compensation must be performed on the acquired images.
In recent years, with the rapid development of microelectronics technology and the improvement of chip manufacturing process, DSP and FPGA have continuously emerged. The signal processing system of a chassis or even a cabinet in the past can now be completely completed by a single DSP or FPGA. System design will also transition from the past PCB board design to VLSI and UVLSI (Very Large Scale Integrated Circuit) chip design. At the same time, due to the massive adoption of DSP and FPGA technology, digital image processing has also undergone major changes in terms of hardware structure. It has evolved from a basic serial structure to a parallel processing structure, and from a single-chip DSP or FPGA processor. Multi-DSP or FPGA processor system, or high-speed processing system with array DSP and FPGA. With the development of society and economy, and people's requirements for the real-time performance of digital image processing systems are becoming higher and higher, the application range of digital image processing systems based on DSP and FPGA in automotive electronic products will become wider and wider, such as Car conference TV, car video phone, car machine vision, etc.
3.3 Car-based adaptive real-time processing based on DSP and FPGA
The clock delay of FPGA can reach nanosecond level, 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 characteristics of the internal structure of FPGA, it can easily implement a distributed algorithm structure, which is very beneficial to the realization of high-speed digital signal processing in automotive electronics. Because automotive electronic products usually require a large number of filtering operations, and these filtering functions often require a large number of multiply and accumulate operations, and through a distributed arithmetic structure, FPGA can effectively implement multiply and accumulate operations. On the other hand, a large number of complex mathematical operations required can be completed by DSP or ASIC composed of DSP cores. In automotive electronic products, special attention is paid to the size, weight, and power consumption of products; in terms of data transmission, the large amount of data generated by the digitization of sound signals in automotive electronic systems depends on high-performance DSP and FPGA to reduce storage space And transmission bandwidth requirements, it is necessary to perform adaptive real-time processing on video signals and audio signals such as encoding, decoding, color space conversion, echo cancellation, filtering, error correction, multiplexing, and bit stream protocol processing. This is often DSP and FPGA cannot be completed.
Control theory processing is a difficult and important issue in automotive electronics. The open-loop, dead-cycle, optimal, and adaptive control systems established by classic and modern control theories are used to realize the optimal control of automobiles. To establish these control systems, first identify a certain system of the automobile, such as the ignition advance angle optimization control system, establish the mathematical model of the system, and then use the corresponding control method to optimize the control. However, the structure of the engine itself is relatively complex, and there are many factors that affect the ignition. It is difficult to theoretically derive the mathematical model to optimize the ignition state. Therefore, the experimental method is generally used to find the optimal ignition advance angle under various working conditions, and then stored in an external memory with increased capacity based on DSP and FPGA or DSP and FPGA array; this can avoid the use of a computer. During the control process, the system detects the working conditions of the engine (such as engine speed, power, etc.) in real time, finds out the optimal ignition advance angle under the working conditions by looking up the table, and then corrects it to control the ignition. Compared with the traditional computer-based control method, on the one hand, it greatly reduces the volume; on the other hand, it is more real-time and flexible. Suspension electronic control refers to a control system that can adaptively process the vehicle's roll, forward and backward, and automatically adjust the damping force of the shock absorber after the computer detects the signal of steering and braking conditions. It can prevent tilt and improve Ground adhesion of wheels, ultrasonic height sensors are used to control the height of the body, air springs are used to adjust the elastic system, grating detectors are used to measure the steering angle and so on. The emergence and development of DSP and FPGA have made the control of various systems centralized, forming an intelligent control system for the entire vehicle.
"Intelligent transportation system" as the common pursuit direction of the future automobile and transportation industry, it will include intelligent highways and intelligent vehicle systems. It combines advanced highway information processing technology and radar anti-collision technology to connect highways and cars as a whole, which can greatly increase the flow of cars and greatly reduce the incidence of traffic accidents. Therefore, automotive intelligent related products have been highly valued by automobile manufacturers. 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 best driving route where the vehicle density is relatively concentrated. "Safety first" is always the first choice for users to buy cars. At present, the hot research of millimeter-wave adaptive collision avoidance radar for cars is developed to solve a large number of traffic accidents caused by collisions on highways. Since the relative speeds between cars on the highway are very high, the frequency difference of the radar echo signal must be extracted in real time. Therefore, the extraction and processing of the frequency difference of the radar echo signal and the feedback control processing of the adaptive anti-collision control system are often implemented by DSP or FPGA.
4 Development Outlook
Looking at the major achievements of automotive technology in recent decades, most of them are breakthroughs in the application of electronic technology. Electronic technology has become an important source of power for the development of the automotive industry. The emergence of DSP and FPGA has brought revolutionary changes to automotive products and automotive electronic technology. The amount of DSP and FPGA used in the world automotive industry has increased dramatically, from the former monolithic DSP or FPGA processor to multi-DSP or FPGA processor, or DSP And FPGA array of high-speed processors. Automobile electronic products based on DSP and FPGA can meet the needs of future automobile development, and in the era of coexistence of multiple models, 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 future automotive electronic technology, the speed of DSP and FPGA will continue to increase. As far as DSP is concerned, the current development is rapid. The main trends are: multiple MACs, more registers, wider program bus and data bus, and higher operating frequency in a single-chip DSP; SIMD and MIMD use ultra-long instructions. As far as FPGA is concerned, due to the adoption of sub-micron technology, it is faster and has 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 anti-lock brake systems, airbags, automatic transmissions, and diesel electronic control systems have only been explored in some universities and enterprises, and have not entered the practical stage. The high and new technology represented by automotive electronic technology is the "bottleneck" of the development of China's auto industry. In view of this situation, China's research on automotive electronic technology should not only focus on energy saving, environmental protection and safety of automobiles, and strive to master their core technologies as soon as possible to narrow the gap with developed countries, but also should focus 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 to develop advanced in-vehicle computing and information processing products, drive the progress of the entire automotive electronic technology, and improve the electronic level of China's automobiles.
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