The future of microcontrollers
14 May 2008
In addition to fulfilling control tasks, electronic devices are now using high-definition sensors to acquire information from the environment to process, save, and reproduce the resulting data
Fingerprint scanners for access control systems, GPS-based navigation, and parking assistance systems for cars, as well as consumer electronics such as digital cameras, are using integrated sensors and high-performance microcontrollers and processors to acquire and process virtually anything that can be heard, felt, seen, or detected by smell. Many wonder if this trend can be used as a baseline for predicting the future evolution of these semiconductor devices.
Near-real-time data processing requires high-performance computing and large, flexible memory capacities for the highspeed, non-volatile storage of large volumes of data. On the other hand, large code memories need hardware-independent, OS-centric organisation of programs, which in turn leads to increased software overhead.
Even though embedded applications range from low-end 8bit versions to high-end 32bit solutions with 1000MIPS performance, users are looking for compatible, scaleable microcontroller platforms whose peripherals and process technology offer sufficient redundancy and compatibility for future projects. This is one of the reasons for the high growth rates in 32bit microcontrollers.
However, the increasing use of microcontrollers in safety-critical applications mandates improved quality and reliability measures in order to meet applicable safety regulations, including IEC 61508 specifications.
The requirements for control units are so dynamic that they can even change during the development of a device. Reprogrammable scaleable computing power and memory density are essential. Consequently, the technologies forming the basis of embedded microcontrollers must support reprogrammability and fast access times at low current drain, as well as the high levels of integration normally implemented when using on-chip flash memory.
MONOS flash is amongst the most advanced and fastest memory technologies for embedded microcontrollers. It allows single-cycle random access speeds of up to 100MHz at junction temperatures of 150°C. Currently scaled to 90nm, the technology is perfectly suited for integrating memories of more than 1Mbyte. In the future, flash memories could even be replaced by MRAM (magnetic RAM), offering short read access times and supporting an almost infinite number of read/write cycles.
Renesas has evaluated embedded MRAM memory arrays based on 130nm technology with more than 10E13 write cycles and access times of less than 10nsec (see figure 2). Due to these characteristics, MRAM is the perfect homogenous memory technology for use as data memory, EEPROM and code memory. The use of MRAM in embedded microcontrollers with process geometries starting at 65nm will revolutionise the functionality of control units, just as the introduction of embedded flash memories once did.
Access times of the embedded memory and power dissipation are limiting the maximum clock frequency and computing power of a chip. Highly-miniaturised CMOS process geometries lead to increasing leakage currents and result in very high power dissipation. For microcontroller applications demanding a lot of processing power, Renesas uses the 32bit SH2A core that offers floating-point support. An expanded cache memory, multiple bus structures and dual or multiple core architectures complement the performance evolution, in terms of process and memory technology.
By using additional fixed or reconfigurable onchip logic, the user can achieve as much as a 32-fold improvement in processing power using the same clock frequency. Applications include 3D graphics accelerators for navigation systems, or object-recognition IP for driver assistance systems. In addition to application-specific IP, encoder/decoder algorithms (including AAC, MP3, WMA, ATRAC3/plus, real audio, and aacPlus), are being used in mobile, car infotainment and digital consumer applications, making the implementation of suitable hardware and software IP in multiple segments look like an attractive option.
Monolithic chip design is not the only way of achieving high levels of integration. Multi-chip packages, including SiPs (systems-inpackage), can be used in space-constrained mobile communications devices or digital cameras. The different chips can be placed side by side or stacked within the package.
Airbags, anti-lock braking systems, medical equipment and industrial automation systems are typically considered as safety critical applications. However, in emergency situations, even simple functions such as door openers and electronic door locks can present a risk. Networked control units and the inclusion of third-party software into the object code might also increase the risk of malfunctions. In order to prevent such faults and avoid accidental or intentional manipulation, nextgeneration microcontrollers will offer many safety features, including self-test functions at start-up or runtime, a supervisor mode to selectively grant read and write access rights, and the timeout supervision of operating-system tasks by independent, non-maskable timer functions. Specifically, these microcontroller functions support the qualification of control units according to established safety standards like IEC 61508.
The proliferation of electronics in almost all aspects of our life will create new megaapplications and continue to drive innovation in the microcontroller sector. Integration projects featuring high levels of processing power, multi-purpose memory technology and convenient implementation of hardware and software IP will play a major role in this context.
MICHAEL LOCH is manager, System Application Group, Automotive Business Unit, Renesas Technology Europe
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