Atmel’s SAM L21 MCU for IoT tops low power benchmark

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SAM L21 MCUs consume less than 940nA with full 40kB SRAM retention, real-time clock and calendar, and 200nA in the deepest sleep mode.

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The Internet of Things (IoT) juggernaut has unleashed a flurry of low-power microcontrollers, and in that array of energy-efficient MCUs, one product has earned the crown jewel of being the lowest-power Cortex M-based solution with power consumption down to 35µA/MHz in active mode and 200nA in sleep mode.

How do we know if Atmel’s SAM L21 microcontroller can actually claim the leadership in ultra-low-power processing movement? The answer lies in the EEMBC ULPBench power benchmark that was introduced last year. It ensures a level playing field in executing the benchmark by having the MCU perform 20,000 clock cycles of active work once a second and sleep the remainder of the second.

 

ULPBench shows SAM L21 is lower power than any of its competitor’s M0+ class chips.

Atmel has released the ultra-low-power SAM L21 MCU it demonstrated at Electronica in Munich, Germany back in November 2014. Architectural innovations in the SAM L21 MCU family enable low-power peripherals — including timers, serial communications and capacitive touch sensing — to remain powered and running while the rest of the system is in a reduced power mode. That further reduces power consumption for always-on applications such as fire alarms, healthcare, medical and connected wearables.

Next, the 32-bit ARM-based MCU portfolio combines ultra-low-power with Flash and SRAM that are large enough to run both the application and wireless stacks. Collectively, these three features make up the basic recipe for battery-powered mobile and IoT devices for extending their battery life from years to decades. Moreover, they reduce the number of times batteries need to be changed in a plethora of IoT applications.

Low Power Leap of Faith

Atmel’s SAM L21 microcontrollers have achieved a staggering 185.8 ULPBench score, which is way ahead of runner-up TI’s SimpleLink C26xx microcontroller family that scored 143.6. The SAM L21 microcontrollers consume less than 940nA with full 40kB SRAM retention, real-time clock and calendar, and 200nA in the deepest sleep mode. According to Atmel spokesperson, it comes down to one-third the power of competing solutions.

Markus Levy, President and Founder of EEMBC, credits Atmel’s low-power feat to its proprietary picoPower technology and the company’s low-power expertise in utilizing DC-DC conversion for voltage monitoring. Atmel’s picoPower technology employs flexible clocking options and short wake-up time with multiple wake-up sources from even the deepest sleep modes.

ULPBench aims to provide developers with a reliable methodology to test MCUs.

In other words, Atmel has taken the low-power game beyond architectural improvements to the CPU while optimizing nearly every peripheral to operate in standalone mode and then use a minimum number of transistors to complete the given task. Most lower-power ARM chips simply disable the clock to various parts of the device. The SAM L21 microcontroller, on the other hand, turns off power to those chip parts; hence, there is no leakage current in thousands of transistors in that part.

Here is a brief highlight of Atmel’s low-power development efforts that now encompass almost every peripheral in an MCU device:

Sleep Modes

Sleep modes not only gate away the clock signal to stop switching consumption, but also remove the power from sub-domains to fully eliminate leakage. Atmel also employs SRAM back-biasing to reduce leakage in sleep modes.

Consider a simple application where the temperature in a room is monitored using a temperature sensor with the analog-to-digital converter (ADC). In order to reduce the power consumption, the CPU would be put to sleep and wake up periodically on interrupts from a real-time counter (RTC). The measured sensor data is checked against a predefined threshold to decide on further action. If the data does not exceed the threshold, the CPU will be put back to sleep waiting for the next RTC interrupt.

SleepWalking

SleepWalking is a technology that enables peripherals to request a clock when needed to wake-up from sleep modes and perform tasks without having to power up the CPU Flash and other support systems. For instance, Atmel’s ultra-low-power capacitive touch-sensing peripheral can run in all operating modes and supports wake-up on a touch.

For the temperature monitoring application, as mentioned above, this means that the ADC’s peripheral clock will only be running when the ADC is converting. When the ADC receives the overflow event from the RTC, it will request its generic clock from the generic clock controller and peripheral clock will stop as soon as the ADC conversion is completed.

Event System

The Event System allows peripherals to communicate directly without involving the CPU and thus enables peripherals to work together to solve complex tasks using minimal gates. It allows system developers to chain events in software and use an event to trigger a peripheral without CPU involvement.

Again, taking temperature monitor as a use case, the RTC must be set to generate an overflow event, which is routed to the ADC by configuring the Event System. The ADC must be configured to start a conversion when it receives an event. By using the Event System, an RTC overflow can trigger an ADC conversion without waking up the CPU. Moreover, the ADC can be configured to generate an interrupt if the threshold is exceeded, and the interrupt will wake up the CPU.

Low Power MCU Use Case

Paul Rako has mentioned a sensor monitor in his recent post in Atmel’s Bits & Pieces blog. Rako writes in his post titled “The SAM L21 pushes the boundaries of low power MCUs” about this sensor monitor being asleep 99.99 percent of the time, waking up once a day to take a measurement and send it wirelessly to a host. Such tasks can be conveniently handled by an 8-bit device.

However, moving to IoT applications, which constitute protocol stacks, there is number crunching involved and that requires a faster ARM-class 32-bit chip. So, for battery-powered IoT applications, Rako makes the case for 32-bit ARM-based chip that can wake up, do its thing, and go back to sleep. If a high-current chip wakes up 10 times faster but uses twice the power, it will still use less energy and less charge than the slower chip.

Next, Rako presents sensor fusion hub as a case study in which the device saves power by skipping the radio chip to send the data from each sensor and instead uses the ARM-based microcontroller that does the math and pre-processing to combine the raw data from all sensors and then assembles the result as a simple chunk of data.

Atmel has scored an important design victory in the ongoing low-power game that is now prevalent in the rapidly expanding IoT market. Atmel already boasts credentials in the connectivity and security domains — the other two key IoT building blocks. Its connectivity solutions cover multiple wireless arenas — Bluetooth, Wi-Fi, Zigbee and 6LoWPan — to enable IoT communications.

Likewise, Atmel’s CryptoAuthentication devices come with protected hardware key storage and are available with SHA256, AES128 or ECC256/283 cryptography. The IoT triumvirate of low power consumption, broad connectivity portfolio and crypto engineering puts Atmel in a strong position in the promising new market of IoT that is increasingly demanding low power portfolio of MCUs to be matched with high performance.

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Majeed Ahmad is author of books Smartphone: Mobile Revolution at the Crossroads of Communications, Computing and Consumer Electronics and The Next Web of 50 Billion Devices: Mobile Internet’s Past, Present and Future.

SAM L family now the world’s lowest power ARM Cortex-M based solution

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Consuming one-third the power of existing solutions, Atmel | SMART SAM L achieves 185 EEMBC ULPBench score.

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System design used to be an exercise in optimizing speed. That has since changed. Nowadays, embedded systems pack plenty of performance to handle a number of task, leading the challenge for designers to shift to completing those tasks using as little energy as possible — but not necessarily making it as fast as possible. As you can imagine, this has created quite the competitive environment on the processor battlefield amongst vendors, each seeking to attain the lowest power solution on the market.

“The surge in popularity of battery-powered electronics has made battery life a primary system-design consideration. In extreme cases, the desire is not to run off of a battery at all, but to harvest energy from local sources to run a system — which requires the utmost power frugality,” writes Andreas Eieland, Atmel Director of Product Marketing. “In addition, there’s a growing family of devices like smoke detectors, door locks, and industrial sensors (4-20 mA and 10-50 mA) that can draw power through their inputs, and that power is limited.”

These sort of trends point to the significance of reducing the power requirements of electronic systems. However, the varying technologies that provide the necessary performance make power reduction harder. Fortunately, Atmel has been focusing on low power consumption for more than 10 years across its portfolio of AVR and Atmel ǀ SMART ARM-based processors. Many integrated peripherals and design techniques are used to minimize power consumption in real-world applications, such as integrated hardware DMA and event system to offload the CPU in active and standby modes, switching off or reducing clock or supply on device portions not in use, intelligent SleepWalking peripherals enabling CPU to remain in deep sleep longer, fast wake-up from low power modes, low voltage operation with full functionality, as well as careful balancing of high performance and low leakage transistors in the MCU design.

With picoPower technology found in AVR and Atmel ǀ SMART MCUs, Atmel has taken it a step further. Indeed, all picoPower devices are designed from the ground up for lowest possible power consumption from transistor design and process geometry, sleep modes, flexible clocking options, to intelligent peripherals. Atmel picoPower devices can operate down to 1.62V while still maintaining all functionality, including analog functions. They have short wake-up times, with multiple wake-up sources from even the deepest sleep modes. Some elements of picoPower technology cannot be directly manipulated by the user, but they form a solid base that enables ultra-low power application development without compromising functionality. Meanwhile, flexible and powerful features and peripherals lets users apply an assortment of techniques to reduce a system’s total power consumption even further.

Then, there’s the Atmel | SMART SAM L21 microcontroller, which has broken all ultra-low power performance barriers to date. These Cortex-M0+-based MCUs can maintain system functionality, all while consuming just one-third the power of comparable products on the market today. This device delivers ultra-low power running down to 35µA/MHz in active mode, consuming less than 900nA with full 32kB RAM retention. With rapid wake-up times, Event System, Sleepwalking and the innovative picoPower peripherals, the SAM L21 is ideal for handheld and battery-operated devices for a variety of Internet of Things (IoT) applications.

The ultra-low power SAM L family not only broadens the Atmel | SMART portfolio, but extends battery life from years to decades, reducing the number of times batteries need to be changed in devices such as fire alarms, healthcare, medical, wearable, and equipment placed in rural, agriculture, offshore and other remote areas. The SAM L21 combines ultra-low power with Flash and SRAM that are large enough to run both the application and wireless stacks — three features that are cornerstones of most IoT applications. Sampling now, the SAM L21 comes complete with a development platform including an Xplained Pro kit, code libraries and Atmel Studio support.

So how does the SAM L21 stack up against the others? Ahead of the pack, of course! As an alternative to so-called “bench marketing” of low power products, nearly ever large semiconductor company — and several smaller ones that focus on low power — have collaborated in a working group formed by the Embedded Microprocessor Benchmark Consortium (EEMBC). The EEMBC ULPBench uses standardized test measurement hardware to strictly define a benchmark code for use by vendors, considering energy efficiency and running on 8-, 16- and 32-bit architectures. At the moment, the Atmel | SMART SAM L21 product boasts the highest ULPBench score of any microcontroller, regardless of CPU.

“In Atmel’s announcement last year for the company’s SAM L21 family, I had pointed out the amazingly low current consumption ratings for both the active and sleep mode operation of this product family – now I can confirm this opinion with concrete data derived from the EEMBC ULPBench,” explained Markus Levy, EEMBC President and Founder. “Atmel achieved the lowest power of any Cortex-M based processor and MCU in the world because of its patented ultra-low power picoPower technology. These ULPBench results are remarkable, demonstrating the company’s low-power expertise utilizing DC-DC conversion for voltage monitoring, as well as other innovative techniques.”

While running the EEMBC ULPBench, the SAM L21 achieves a staggering score of 185, the highest publicly-recorded score for any Cortex-M based processor or MCU in the world — and significantly higher than the 167 and 123 scores announced by other vendors. The SAM L21 family consumes less than 940nA with full 40kB SRAM retention, real-time clock and calendar and 200nA in the deepest sleep mode.

In fact, a recent EE Times writeup delving deeper into competition even revealed, “TI surpassed its own earlier result by announcing the MSP-432 family based on the Cortex M4F. It achieved a ULPBench score of 167.4. While TI was briefing the media on this product, however, Atmel quietly published a ULPBench score of 185.8 for its SAM L21 MCU based on the Cortex M0+.”

Beyond the recently-unveiled ARM-based chip, it’s also important to note the 0.7V tinyAVR. A typical microcontroller requires at least 1.8V to operate, while the voltage of a single battery-cell typically ranges from 1.2V to 1.5V when fully charged, and then drops gradually below 1V during use, still holding a reasonable amount of charge. This means a regular MCU needs at least two battery cells. Whereas, Atmel has solved this problem by integrating a boost converter inside the ATtiny43U, converting a DC voltage to a higher level, and bridging the gap between minimum supply voltage of the MCU and the typical output voltages of a standard single cell battery. The boost converter provides the chip with a fixed supply voltage of 3.0V from a single battery cell even when the battery voltage drops down to 0.7V. This allows non-rechargeable batteries to be drained to the minimum, thereby extending the battery life. Programmable shut-off levels above the critical minimum voltage level avoid damaging the battery cell of rechargeable batteries.

Interested in learning more? You can explore Atmel’s low power technology here, as well as download the new white paper entitled “Turn Power-Reducing Features into Low-Power Systems” here.