How to choose a processor in a car electronic system

Cars are experiencing the baptism of a digital revolution: the era of purely mechanical systems and analog electronics is gone forever. Today's cars are digital cars with dozens or even hundreds of embedded processors that are connected to each other via a digital network to control and optimize the operation of almost every system in the car. Future vehicles will integrate more processors because advanced applications and performance require more sophisticated signal processing algorithms, including safety, engine and exhaust emissions control, driver-to-car interface, and in-car information and entertainment systems. Wait.

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The automotive market requires processor vendors to make long-term commitments. For example, automakers sometimes require their suppliers to provide a 10 to 15 year supply commitment to a processor product. Below we will explore the various processor types for automotive digital signal processing applications, as well as the advantages and disadvantages of each type. In addition, we will analyze the impact of special requirements for automotive applications on processors for the automotive market.

Schedule: Processor Type, Representative Vendor, and Processor Sample

Processor selection in automotive applications

The choice of processor used in automotive systems is influenced by a number of factors. The most important selection criteria generally include automotive certification, on-chip integration, performance, price, and energy efficiency. The quality of software development tools and the availability of software components also affect the choice of processor. Processor vendors' commitment to their products and future development plans are also important considerations.

Due to life safety, critical automotive safety systems such as automotive engines, airbag controls and brake systems have very stringent requirements for durability and durability. Therefore, automotive safety system applications are the most severe test for processor vendors. These applications require the processor to qualify for automotive certification, and such processors require specialized design, manufacturing, packaging, and testing methods.

There are many non-critical signal processing automotive systems that also require a large number of processors, such as in-car navigation and entertainment equipment. Although automotive OEMs and automotive electronics suppliers require high-quality components for such applications, the requirements are not as high as critical safety applications. For example, processors used in in-vehicle systems generally do not require automotive certification.

Today, the most demanding automotive signal processing applications are in-car navigation and entertainment systems. In a few years this may change, as new security systems begin to use video and radar processing, and engine and brake control systems will use complex model-based calculations. The current lookup table reference method will also be complicated. The real-time operation method is replaced.

Integrating the appropriate peripherals, memory, and I/O interfaces on the processor helps improve performance and stability, as well as reduce power and system cost. The on-chip integration requirements for automotive applications are quite different from other signal processing applications. Therefore, suppliers for the automotive application market must design their processors specifically for the specific requirements of these applications. Multi-channel analog-to-digital converters are particularly useful for processors that are oriented to automotive control systems. For example, an engine control system typically receives input signals from dozens of analog sensors.

On-chip flash is a key feature for processors targeting automotive control systems because these systems use large lookup tables and sometimes require field updates. The lookup table used by the engine control system contains tens of thousands of calibration points (or similar output values) from various control components such as oilers and ignition coils. Calibration point data is generally determined in the laboratory before the car leaves the factory, but some calibration points may need to be adjusted after the car has been in use for some time. On-chip flash memory can be used to update calibration points or other parameters of the control algorithm in the field using data downloaded from a car dealership.

The biggest benefit of integrating flash memory on a processor compared to using a separate flash chip is system performance improvement and cost reduction. While integrated on-chip flash is valuable to system developers, it is not easy for processor vendors to implement it. Automotive-certified processors require higher temperatures than the mainstream flash technology can withstand. It is conceivable that processor vendors competing in this market often need to invest a lot of resources to develop flash technology that can work stably on automotive systems.

Digital network transceivers facilitate communication between processors in a distributed system. There are a variety of network protocols for different automotive systems. Processors for specific automotive applications typically integrate a network transceiver for the relevant protocol. For example, the Control Area Network (CAN) protocol is typically used for engines and variable speed control networks. The Media Oriented System Transfer (MOST) protocol targets in-car infotainment applications such as audio, video, navigation, and communications.

Advanced on-chip debug tracing units are also useful for processors for critical applications. This tracking provides system developers with detailed processor, software, and operating system status information that is especially useful for verification and debugging. The Nexus 5001 Forum standard for global embedded processor debug interfaces defines the interface between software and on-chip debug hardware. The standard was first developed by the IEEE Industry Standards and Technology Organization (IEEE-ISTO) in 1999 and has been updated to IEEE-ISTO 5001-2003. Developers of the standard hope it will encourage development tool vendors to add or enhance support for on-chip debug tracking units.

In-vehicle information and entertainment systems are the most demanding signal processing systems in current automotive applications, primarily because they involve applications such as video processing that require powerful signal processing. A high-end infotainment system may include a multi-channel audio system, a DVD player, a GPS navigation system, and a hands-free mobile phone, all integrated into one system. Processors for in-vehicle infotainment systems include relatively high performance DSPs, DSP enhanced general purpose processors (GPPs), and DSP/GPP hybrid devices. These processors typically operate over a range of clock rates from 200 to 750 MHz.

Conversely, processors for critical control systems such as engine and brake control are generally medium performance processors. Larger chip manufacturing processes (such as 0.18 or 0.25 microns) are more likely to meet the requirements of harsh operating environments such as high temperatures, and the processing speed requirements for control applications are generally not too high. Therefore, a relatively low maximum processor clock speed (40 to 150 MHz) and a large manufacturing process are the best choice for this type of application. However, the processing performance requirements of such applications are also increasing, and processor vendors must adjust their strategies to achieve higher performance while meeting high temperature requirements.

Automotive applications are particularly sensitive to price. Processor vendors have to develop highly integrated dedicated processors to reduce system cost. While automotive applications are price sensitive, the automotive qualification process is costly and these costs increase chip cost. As a result, automotive-qualified processors are generally more expensive than non-certified counterparts. In automotive signal processing systems, energy efficiency is generally not a major issue. The engine, chassis and brake control systems are only active when the engine is running and the battery charging system is activated.

Still, energy efficiency is important in some applications. Some systems are active when the engine is off, and their power consumption must be low so that battery drain does not affect engine startup. For example, in-car infotainment equipment is one such application. Still others must be well sealed to protect them from the outside environment. In this case, the package of such a system may affect heat dissipation, so the power consumption cannot be too large.

Signal processor for automotive applications

In today's automotive systems, there are many types of chips used to perform signal processing tasks, from 8-bit MCUs to DSPs to FPGAs. In systems where signal processing plays an important role, 8-bit and 16-bit MCUs are now infrequently used because of their limited processing performance. To reduce costs, system developers often choose processors that perform just fine. However, for some applications, it is wise to reserve some performance space, especially in-car infotainment systems, which can benefit from the flexibility of this performance space, because of some functional applications (such as speech recognition, navigation and audio). Control) has not developed well when choosing a processor.

The 32-bit embedded general purpose processor (GPP) is generally used for automotive signal processing control systems with medium performance requirements. This level of processor is generally RISC structure, the instructions used are simple, common and almost no parallel instructions. GPP is particularly effective at algorithmic processing that emphasizes decision making and control flow changes, but in many cases its signal processing performance is also good. In addition, GPP is also a good compiler object. GPP compiled code is quite efficient compared to some special DSP structures that are difficult to compile. Popular 32-bit GPP architectures (such as MIPS, ARM, and PowerPC) have been widely used in automotive and non-automotive applications.

The benefits of broad market acceptance include a rich supply of third-party software components and strong development tool support. Processors in this category include Texas Instruments' TMS470 family (based on the ARM7 core) and Freescale's MPC500 family (based on the PowerPC core). Both processors integrate automotive-specific peripherals on a 32-bit general-purpose processor core. Freescale's MPC500 family of processors integrates peripherals, memory and dedicated I/O interfaces for engine and variable speed control applications with high-capacity flash memory, multiple CAN interfaces, a Nexus debug interface, and multiple ADCs And several advanced timing modules.

DSP, DSP/GPP hybrid devices, and DSP-enhanced GPP are generally used in in-vehicle infotainment systems and control systems that require signal processing functions. These processors come with special features, including multi-aggregation hardware, high-capacity storage bandwidth, and instructions for multi-run algorithms. These features combine to greatly accelerate digital signal processing algorithms, much faster than GPP at the same clock rate.

DSP/GPP hybrid devices and DSP-enhanced GPP are intended to integrate the best features of DSP and GPP: the signal processing capabilities of DSP and the high efficiency of GPP in decision-intensive algorithms and compiled code. This combination of functions is especially important for systems that require both signal processing and decision processing. Such processors include Texas Instruments' TMS320C2000 series, Freescale's MC56F83xx series, Renesas' SH7760, and Analog Devices' ADSP-BF53x (Blackfin series).

FPGAs don't seem to be suitable for automotive processing applications because they have always been known for being expensive. However, in recent years, FPGA vendors have introduced a series of low-cost, high-efficiency devices that make FPGAs an alternative to automotive systems. Unlike traditional fixed-structure processors such as DSP and GPP, FPGAs are not limited by the pre-set instruction set. In contrast, FPGAs offer system designers tremendous design flexibility to develop processing structures for specific applications.

Because FPGAs have powerful parallel processing capabilities, their signal processing speed is faster than the fastest fixed-structure processors. But high performance comes at a price: the development cost of FPGA-based signal processing systems is much higher than the cost of fixed-structure software development. Although the role of FPGAs in automotive systems will gradually expand, it is currently mainly used for the interface of in-car infotainment systems. Of course, once the FPGA enters the automotive system, it has many other uses that may replace the functionality of other system components.

For example, with the advent of "soft" processor cores with FPGAs, like Altera's Nios II and Xilinx's MicroBlaze (both are 32-bit RISC processor cores), microprocessors may use more FPGAs. Implemented instead of a separate chip. This saves money because soft cores can be customized (designers can include and eliminate certain features, as well as trade-offs in functionality and resource consumption), and are also easy to implement with dedicated hardware using FPGA fabrics (such as specific algorithm accelerators). Interface.

Digital signal processors spread all over the car

As automotive applications become more electrically and electronically controlled, digital signal processing will spread throughout the car. Applications that already use digital signal processing will increase the computational load, driving the development of a new generation of high-performance automotive processors. For example, Freescale's new MCP5554 processor runs twice as fast as its predecessor, the MPC566, and the new SIMD instruction execution further enhances its signal processing performance.

New applications in digital signal processing in the automotive sector include both computationally intensive applications that require high signal processing performance (such as lane tracking systems) and applications that require only general processing performance (such as tire pressure monitoring systems - TPMS). Processors for automotive signal processing applications have a wide range of performance and will become more diverse in the future. High-end applications such as video-based security and infotainment systems will require higher signal processing performance, while low-end applications such as TPMS require energy-efficient and efficient processing.

More processors, a wider range of performance, when is this trend at the end? Maybe wait until the embedded processor penetrates into every corner of the car system. Imagine this scenario: in addition to the air pressure monitor integrated into each tire (new cars will be enforced), each tire also has a built-in processor for collecting and forwarding information about its status and performance. For example, the tire may automatically issue a warning: "This is the right front tire. I noticed that the road surface is wet, but my tread pattern depth is not enough to cope with this situation."

You might think this is a bit too advanced, but using more processors in the car system will be an irreversible trend. Given the ever-decreasing cost of semiconductor products and the potential benefits of smart car devices, one can expect that one day our cars will be equipped with smart tires.