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Outlook 2010: The key to energy reduction

Outlook 2010: The key to energy reduction

There has been a steep decline in global demand for microcontrollers over the few months. By the end of this year, the market is expected to be some 25% smaller than its 2007-2008 levels of around $13.7billion.

The automotive sector has taken a big hit, as has the manufacturing sector; until recently, both sectors were seeing strong growth opportunities.

However, with the markets expected to recover during the next few quarters, the 32bit microcontroller market is set to show strong growth, fuelled by several newly emerging technologies.

One of the biggest drivers will be the expanding range of ARM Cortex processor cores, offering semiconductor vendors and end users a greater choice and a much closer fit to specific energy efficiency applications such as e-metering, lighting, household appliances and manufacturing automation.

The automotive sector will also recover in time and looks set to embrace a much more energy efficient approach than it has previously. The ARM ecosystem – bringing together processor cores and software development, combined with an ever widening array of peripheral and mixed signal subsystems – is driving competitively priced 32bit solutions and greater customer choice at an unprecedented rate.

Meanwhile, advances in process, libraries, physical IP and low power methodologies are combining to reduce the active and standby power consumption of the microcontroller and system to levels lower than existing popular 8bit and 16bit architectures. An obvious conclusion is that these technology advances will continue to be driven by economy of scale and thus will work to the advantage of the largest and most popular embedded ecosystem.

NXP Semiconductors has been at the forefront of this trend over the last five years, bringing a range of high performance ARM based MCU families to the market.

This started with the ARM7TDMI-S based LPC2000 family, offering unprecedented price/performance by using a high performance 128bit wide interface to on chip flash memory. Next came the first LPC3000 ARM926EJ microcontroller. Manufactured using a 90nm process, the part operated from supplies as low as 0.9V while running at up to 270MHz. Next came the the LPC2900 ARM968 with on chip flash memory performance increased to 125MHz.

These designs were largely driven by performance requirements, with emphasis on managing power within conventional EDA flows, including extensive clock gating to reduce active power levels.

System approach to low power
The introduction of the NXP LPC1700 Cortex-M3 based family in 2008 saw more of a system level approach taken, in conjunction with the design team from ARM.

The Cortex-M3 core was redesigned for lower overall power consumption targets and new features added to the interrupt system controller to enable low power system sleep and deep sleep modes to be controlled directly by the user software. One consequence of this system approach is the delivery of the wake up interrupt controller separately from the core. This allows for its implementation in a dedicated ultra low power domain.

In addition, system level power simulation and design performance tools were used to determine the optimum memory and bus interfacing for the lowest power consumption, while achieving target performance.

Taken together, these approaches saw overall reductions in power consumption of 30 to 40% at the same frequencies. Perhaps more surprisingly, more efficient memory interface and timing improved overall performance to 100MHz, with the next product releases already achieving 120MHz.

Another conclusion which can be drawn is that, by paying closer attention to low power efficient design techniques, higher overall performance can be achieved. Further product development for lower power applications with the NXP LPC1300 family has seen active power levels of 200µA/MHz achieved for the first time in a 32bit MCU.

While developing the low power techniques with the Cortex-M3 r2p0 processor release, it became clear that there was considerable potential to develop an ultra low power small scale Cortex processor core with the footprint of existing 8bit or 16bit core, but with significantly increased performance efficiency and reduced energy usage.

This core, the Cortex-M0, was announced by ARM in February 2009. Using the well established Thumb (v6M) instruction set, the core supports extremely small code size and efficiency. It also takes advantage of a number of system instructions from the Cortex-M3 r2 and the Cortex-M1, including the low power sleep modes.

The development team at ARM has not only accomplished the challenging target of reducing the core size to less than 15,000 gates – similar to a typical 8 or 16bit core – but, by careful attention to system level power modeling, has also managed to reduce the active power such that the core achieves twice the power efficiency. A similar reduction has been made in low standby power through state retention techniques directly in the core delivery.

Process, libraries and physical IP
Equally important in achieving ultra low power design is the evolution of low leakage process nodes from silicon foundry partners.
One such example is TSMC's 0.18µm Ultra Low Leakage (ULL) process, where leakage reduction has allowed designers to 'wind the clock back' to the 0.35µm era. This, combined with low power library IP, memories and low voltage design and characterisation, is allowing NXP's design teams to achieve significantly lower power and energy usage than previous generations of 8/16 bit microcontroller processes.

ARM has also taken care in matching the libraries and state retention IP to the Cortex-M0 core, making a highly synergistic combination. In case this leads the reader to think that this reduces the differentiation between MCU vendors, then clearly this is only the beginning in realising real world customer designs.
This must be combined with a significant understanding of how to achieve multiple power domain functionality within an overall mixed signal MCU design. The key to offering customers value from all this progress in ultra low power technology lies in combining specialised application peripherals and mixed signal sub systems requirements with advanced low cost 32bit ultra low power MCUs.

Software development
Clearly, with these new core and flexible low power technologies, it will be vital to offer users more than the simple to use development tools and systems they currently get from 8bit and 16bit vendors.

ARM has stepped in here to offer a common driver standard (CMSIS) across the Cortex-M range of processor cores and – more recently, with the launch of mbed.org and the mbed microcontroller rapid prototyping tools – the industry's first online platform for fast, low risk prototyping of microcontroller based systems.

One of the more far reaching aspects of this community based online approach will be the wider sharing of project solutions. Another emerging trend will be the migration to Eclipse based development platforms, where not only will it be important to offer the full range of development features and third party plug ins, but also to offer entry level users a more accessible step on the open source ladder.

Last, but not least, software libraries and kernels will need to be optimised separately for both Cortex-M0 and M3 and installed in on chip resources, together with complex device drivers provided by the MCU vendor.

In the future, it appears that microcontrollers will take advantage of specialised ultra low power technologies, allowing them to drive ever more energy efficient applications.
Starting in 2010, ARM based microcontrollers will compete across the whole spectrum of 8, 16 and 32bit architectures and in most high growth market sectors.


NXP is a leading semiconductor company founded by Philips more than 50 years ago. Headquartered in Europe, the company has about 29,000 employees working in more than 30 countries and posted sales of $5.4billion (including the Mobile and Personal business) in 2008.

NXP creates semiconductors, system solutions and software that deliver better sensory experiences in TVs, set top boxes, identification applications, mobile phones, cars and a wide range of other electronic devices.

Author
Geoff Lees, vice president and general manager, microcontroller division, NXP Semiconductors

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