New ARM-powered chip aims for battery life measured in decades
The number of things getting plugged into the “Internet of Things” has already reached the point of satire. But there’s a new, extremely low power technology that’s being prepared for market that could put computing power and network access into a whole new class of sensors, wearables, and practically disposable devices. That’s because it can run off a battery charge for over over 10 years.
Atmel, the San Jose-based microcontroller maker, today released samples of a new type of ultra-low power, ARM based microcontroller that could radically extend the battery life of small low-power intelligent devices. The new SAM L21 32-bit ARM family of microcontroller (MCUs) consume less than 35 microamps of power per megahertz of processing speed while active, and less than 200 nanoamps of power overall when in deep sleep mode—with varying states in between.
The chip is so low power that it can be powered off energy capture from the body, as Andreas Eieland, Atmel’s Director of Product Marketing for low-power products, demonstrated at CES earlier this year.
The majority of existing low-power MCUs operate in the range of about 120 to 160 microamps per MHz of processing speed, according to Eieland, who spoke with Ars this week. Based on the Embedded Microprocessor Benchmark Consortium’s (EEMBC’s) ULPbench ultra-low power benchmark, the L21 is the lowest power microprocessor ever, achieving a score of 185—50 percent higher than that of the closest competitor (STMicro’s STM32L4) and of Atmel’s last generation of low-power MCUs.
Beyond reducing the amount of power required per MHz, Eieland told Ars, “now it’s down to doing everything you can to reduce power consumption—how can I make sure that this device is tailorable enough in power consumption for the most applications.” That is the thinking that led to the use of multiple power “domains” for varying levels of activity.
“In traditional sleep modes, you’d just gate away the clock (to stop power dissipation from switching)” Eieland said—that is, switch off all the functionality of the controller except its clock-keeping capability to keep it synchronized with the rest of the world when it wakes up again. “What we’ve done on the L21 is that we have five power domains—we don’t just gate away the clock, but we can also take away leakage (of power)from unused modules.” This capability includes a mode that allows peripheral devices to continue to communicate with each other when the CPU core is essentially asleep.
The L21 MCU uses a 42 MHz Cortex M0+ CPU core—the smallest 32-bit ARM processor. It also carries up to 256 kilobytes of Flash memory, up to 32 kilobytes of static RAM, and up to 8 kb of separate low-power static RAM that is kept powered at everything short of the deepest sleep mode—even off a low-power backup battery when the main battery is exhausted.
The processor may not be enough to, say, run an Ubuntu desktop, but it’s certainly enough computing power and memory to run a real-time operating system with multiple programs, handle physical interfaces, stream media from a USB device or other external storage, and tweet you when your dishes are clean. It also can handle a lot of tasks that can reduce the power usage of other components in a device.
Among the updated peripherals supported through the L21’s multiple power management system are a touch interface controller (for buttons, sliders, wheels, and touch-sensitive surfaces), an AES encryption module, a True Random Number Generator (TRNG), and up to four configurable custom logic inputs and outputs for connecting serial communications pinouts on general-purpose printed circuit boards. The AES and TRNG peripheral capabilities make the L21 a good fit for applications like providing hardware-based virtual private network authentication and encryption (sort of like the Exokey from x.o.ware we tested recently).
As part of the sample release, Atmel is also offering kits based on the L21 for developers in the form of the SAML21 Xplained Pro (XPRO) evaluation board for rapid protyping. The XPRO board includes onboard debugging and power usage profiling, and comes with the free Atmel Studio integrated development environment to tap into those features. Pricing has not been announced.