What drives automotive processor selection?

A multitude of factors influence processor selection for automotive systems. The most important selection criteria typically include automotive qualification, on-chip integration, performance, price, and energy efficiency. Software development considerations—such as the quality of development tools and availability of software components—also influence selection. The vendor’s commitment to the product and the processor road map are also important factors.

Automotive qualification

Safety-critical automotive systems, such as engine control, air-bag control, and braking systems, require processors with extreme reliability and durability—life and limb are on the line. As a result, safety-critical automotive applications are the most challenging automotive applications for processor vendors. These applications require “automotive qualified” processors; producing such processors demands specialized design, fabrication, packaging, and testing methods. (See the Special Requirements article for further details on automotive qualification.)

There are also many non-critical signal-processing-intensive automotive systems that rely heavily on processors, such as in-cabin navigation and entertainment equipment. While auto and auto sub-system manufacturers demand high-quality components for such applications, requirements are not as stringent as for safety-critical applications. For example, the processors used in in-cabin systems are generally not automotive qualified.

Today, the most performance-hungry automotive signal processing applications are in-cabin navigation and entertainment systems. This will change in the next few years, though, as new safety systems begin to incorporate video and radar processing, and as engine and braking control systems adopt more computationally demanding model-based approaches, in which complex run-time calculations replace the look-up table references that are prevalent today.

On-chip integration

Having the right kinds of peripherals, memory, and I/O interfaces integrated with the processor can improve performance, reduce energy consumption, increase reliability, and help lower system costs. The on-chip integration that is relevant for automotive applications is often quite different from that required for other signal processing applications. Hence, vendors targeting automotive applications generally tailor their processors for these applications.

Multi-channel analog to digital converters (ADCs) are particularly useful for processors targeting automotive control systems. An engine control system, for example, receives signals from about a dozen analog sensors that monitor operating parameters such as throttle position, engine speed and temperature, intake air density, and exhaust gas oxygen content. Figure 1 shows a typical engine control system. After digitizing, filtering, and analyzing these input signals, the controller generates updated fuel injection and ignition outputs.

Integrated flash memory is a key feature for processors targeting automotive control systems, since these systems often make use of very large look-up tables that occasionally must be upgraded in the field. For example, an engine control system like the one shown in Figure 1 may use look-up tables containing tens of thousands of calibration points, or equivalently output values, for the various components it controls (such as fuel injectors and ignition coils). The calibration points are usually derived empirically in a laboratory, but after a vehicle has been put into service some calibration points may require adjustment. Flash memory provides the flexibility to easily upgrade calibration points or other aspects of the control algorithm in the field via a download at the dealer's service department. The key benefits of integrating flash memory with the processor (as opposed to using discrete flash memory chips) are improved performance and reduced system costs.