Peter Clarke
(02/23/2009 5:06 AM EST)
URL: http://www.eetimes.eu/design/214502333
With help from lead partner and licensee NXP, ARM Holdings plc has designed a very low gate-count ARM processor core suitable for use in microcontrollers aimed at ultra-low power applications. Chips are expected to ship from licensees before the end of 2009.
LONDON -- With help from lead partner and licensee NXP, ARM Holdings plc (Cambridge, England) has designed a very low gate-count ARM processor core suitable for use in microcontrollers aimed at ultra-low power applications. Chips are expected to ship from licensees before the end of 2009.
The processor core, previously codenamed Swift and now called Cortex-M0, looks set to be one more (last?) nail in the coffin of the 8-bit microcontroller as well as enabling ARM and its licensees to engage in applications mandated on energy efficiency, such as wireless sensor nodes and e-metering.
And with just 12,000 gates the Cortex-M0 core has been designed expressly for low power consumption and could find many applications — although ARM is by no means the first company to offer a low gate-count processor core.
The Cortex-M0, which has not yet been implemented in dedicated silicon, is behind the established Cortex-M3 core both in terms of performance and complexity. But that reduced complexity has the benefit of producing a low-cost and potentially very low-power implementation of the ARM 32-bit processor architecture.
The Cortex-M0 offers 32-bit performance in the footprint of a 16-bit processor, enabling 8-bit MCU developers to "skip" 16-bit devices and move directly to 32-bit, ARM claimed, but with the advantage of remaining compatible with the established Cortex-M3 and with the Cortex-M1, which is ARM's synthesizcable microcontroller core for use in FPGAs.
The low gate-count also allows the M0 to be implemented in what is essentially the digitization of analog or mixed-signal chips, the company said.
"We will supply M0-based components before the end of 2009," said Geoff Lees, general manager of the microcontroller division at chip company NXP BV (Eindhoven, The Netherlands). NXP has only been in the market with Cortex-M3 microcontrollers since October 2008, nonetheless Lees has clearly has applications in mind for the M0 in the industrial, consumer and medical sectors.
"Low power e-metering, consumer peripherals such as MP3 accessories, power management &@151; there's a new charging standard coming in based on micro-USB. Automotive will be a strong market, eventually. But right now automotive is on its knees," Lees said. "And then anything to do with energy harvesting and renewable energy," he said.
Richard York, director of product marketing for ARM's processor division, said: "For certain markets the Cortex-M3 is too big in terms of performance and in terms of power consumption, for example where we are replacing state machines and dedicated logic."
The Cortex-M0 offers comparable performance to the synthesizable version of the ARM7TDMI and has been benchmarked at 0.9 dhrystone MIPS/MHz and 0.85-microwatt/MHz in the 180ULL process from Taiwan Semiconductor Manufacturing Co. Ltd. According to ARM documentation the Cortex-M3 processor performs at up to 1.2-DMIPS/MHz with a core of 33,000 gates.
Lees made it clear that NXP's strategy is based not only on the microcontroller core but also on the design style and manufacturing process technology, in fact, doing everything together to drive down dynamic and static power consumption.
There is a strong synergy with the ARM physical IP such as memory for the microcontroller. NXP has made use of the ARM SRAM compiler, Lees said. "SRAM can be up to 40 percent of the die so it is vital to have that as low-power as possible. And the 180ULL process is just about the best process for low-leakage flash process."
Lees said he sees a bipolar distribution for Cortex-M0 with some implementations on mixed-signal processes at 0.18-micron or higher nodes and others with a Cortex-M0 thrown on to a leading-edge system-chip at 65-nm or 40-nm to do a dedicated function such as touch-screen control in mobile phone.
According to ARM's York, the secret of developing a compact processor core comes down to a clean-sheet design. "The instruction set is well-defined. It's a three-stage pipeline [like the M3]; some instructions take multiple cycles, some take one cycle," said York.
However, one way to strip out the complexity is drop the RISC principle of single-cycle execution and things such as speculative execution. The M0 is built of control and power efficiency not for speed. "M3 has got much richer maths instruction execution," said York.
The M0 maintains the nested vector interrupt controller (NVIC) and the wake-up interrupt controller (WIC) from the M3 design, which is one of the keys to allowing the Cortex-M0 to start up quickly, execute and then fall back to energy-conserving sleep mode. The result is the M0 occupies about one-third the area and consumes about half the dynamic power of the M3, according to York and Lees. ARM supplies serial debug features, but allows licensees to configure how much they need.
And Both the M3 and the M0 make use of the ARM AMBA bus as the means to link peripherals to the core. As a rule ARM does not license microcontroller peripherals to microcontroller companies, that being the way they add value. But ARM has taken the direct memory access (DMA) controller out of the processor core and implemented a mini DMA memory controller as AMBA-bus peripheral.
Not the first
However, Cambridge Consultants Ltd. (Cambridge, England) where pioneering the ultra-compact RISC processor some 15 years before ARM.
Alistair Morfey a design engineer with Cambridge Consultants, started with a 16-bit XAP processor in 1994 specifically to support embedded applications that Cambridge Consultants was developing for its clients in such sectors as industrial, low-cost consumer and medical sectors.
The XAP2 microcontroller used to be provided in the form of process-portable Verilog at the register transfer level. That processor synthesized to around 12,000 gates — about the same as the M0 — and was designed-in to Bluetooth chips made by CSR plc. Other licensees include Chipcon, subsequently bought by Texas Instruments, Cyan Technology, Ember Corp. and GreenPeak Technologies.
Cambridge Consultants also pioneered a royalty-free model in the early days of licensing the XAP, which has subsequently been updated with 32-bit versions. The XAP energy-efficient processors are now in over a billion chips so ARM already has competition in the field.
According to NXP's Lees the microcontroller market is worth $15 billion per annum with $3 to $5 billion having been won over to 32-bit solutions. "That means the 8/16-bit MCU market is still worth $10 billion," said Lees saying that was the market that M0 could take.
NXP's microcontroller history although strongly based on the 8-bit 8051 has more recently been based on the ARM926 and the Cortex-M3. Lees said: "We wouldn't license a core with a completely different instruction set. If you have a vision of supporting 10 companies the infrastructure is much more important."
The Cortex-M0 is supported by third-party tool and RTOS vendors including CodeSourcery, Code Red, Express Logic, IAR Systems, Mentor Graphics, Micrium and Segger. The Cortex-M0 processor is compatible with the recently-launched Cortex Microcontroller Software Interface Standard (CMSIS), a hardware abstraction layer for the Cortex-M processor series (see ARM group seeks to extend microcontroller software reuse).
The CMSIS enables consistent software interfaces to the processor for silicon vendors and middleware providers, simplifying software re-use, reducing the learning curve for new microcontroller developers and reducing the time-to-market for new devices.
Lees said it was an imperative of NXP's lead partner status that the M0 use the same C language compiler as the M1 core. "There is the addition of a 'deep sleep' instruction but that is a major benefit and is worth the exception."
The new processor extends the company’s MCU roadmap into ultra low-power MCU and SoC applications such as medical devices, e-metering, lighting, smart control, gaming accessories, compact power supply, power and motor control, precision analog and IEEE 802.15.4 (ZigBee) and Z-Wave systems. The Cortex-M0 processor is also suitable for the programmable mixed signal market with applications such as intelligent sensors and actuators which have traditionally required separate analog and digital devices.
"By providing 32-bit performance in a 16-bit footprint, the ARM Cortex-M0 processor, enables us to reduce silicon and energy costs without compromising product enhancements or upward code compatibility, making it an ideal complement to the Cortex-M3 architecture that we use across our products," said Lees.
Triad Semiconductor Inc. (Winston-Salem, North Carolina) is also an early licensee of the Cortex-M0. Triad designs and manufacturers mixed signal ASICs and in particular offer structured ASICs through the use of Via Configurable Array (VCA) technology with single-mask layer configuration.
"Smart sensors are an ever growing requirement in a wide range of next-generation applications from industrial, to medical and automotive," said Jim Kemerling, chief technology officer of Triad Semiconductor, in a statement. "Combining the ARM Cortex-M0 processor with our silicon-proven configurable analog and digital technology will provide Triad Semiconductor customers with the fastest, safest and most cost-effective way to design, prototype and produce advanced mixed signal ASICs."
This arrangement Triad is calling Mocha and through the single-mask layer the same piece of silicon can be configured as: dual-channel sensor interface, a BLDC motor controller; an RGB LED Driver plus capacitive touch; or a hysteretic controller.
"Mocha-1 will be available for customers by the end of the year; prototypes in Q3 and production in Q1 of 2009," said Reid Wender, vice president of marketing. Wender said Triad was working with Austriamikrosystem to produce the Mocha-1 in a 0.35-micron process technology.
Two other notable ARM licensees not included in the recent M0 announcement are Luminary Micro Inc. (Austin, Texas) and, Energy Micro A/S (Oslo, Norway). Luminary was ARM's lead partner for the introduction of microcontrollers based on the Cortex-M3. Energy Micro AS is working on an ARM Cortex-M3 based microcontroller family due to start shipping in August 2009. It is pledged to produce the most "energy-friendly" microcontrollers.
ARM's York declined to comment on whether Luminary and Energy Micro were active licensees of the Cortex-M0. The ARM Cortex-M0 is available for licensing immediately.
Companies mentioned in this article
ARM Holdings plc
NXP BV
Cambridge Consultants Ltd.
CSR plc
Cyan Technology Ltd.
Ember Corp.
GreenPeak Technologies NV
Triad Semiconductor
Energy Micro AS
Luminary Micro Inc.
Express Logic
Mentor Graphics
Related articles:
Fifth XAP processor core targeted at wireless applications
Russian design house focuses on Cortex-M3 for automotive applications
ARM set to cut 3% of jobs, imposes pay freeze
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