Reduce IoT power use with Atmel SAM L21

13th April 2015

One of the latest and most power-efficient 32-bit microcontroller options on the market today is Atmel’s new SAM L21 MCU family, specifically aimed at power-efficient battery powered devices in wireless sensor networks and the accelerating Internet-of-Things market.

The Atmel SMART SAM L21 family, based on the ARM Cortex-M0+ core, boasts ultra-efficient current consumption as low as 35 micro amps per MHz with the chip in active mode and as low as 200 nano amps in the deepest sleep mode.

This best-in-class power efficiency is said to have the potential to “extend battery life from years to decades” in power-optimised sensor network and Internet-of-Things applications. These chips draw less than 1 micro amp with full SRAM retention, real-time clock and calendar running, making the SAM L21 family the lowest-power Cortex-M based microcontroller solution on the market.

With a 42 MHz Cortex-M0+ core, which is the smallest 32-bit ARM core, 256 kB of flash memory and up to 40 kB of SRAM, these chips obviously aren’t intended to compete with high-end mobile processors in terms of performance. However, these small, power-efficient microcontrollers are still powerful enough to support touch interfaces, AES encryption, and wireless communications – for example running both the application and wireless stacks in a typical wireless end-node IoT application.

Also included is up to 8 kB of separate low-power SRAM 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 Cortex-M0+ is a fairly modest embedded ARM core in terms of its relative performance – it’s an optimised version of the Cortex-M0, with one less pipeline stage to reduce power consumption and with a few features from the more capable Cortex-M3 and M4 families also added.

The SAM L21 is the lowest-power Cortex-M0+ based device family presently on the market, and it expands Atmel’s product offering beyond the SAM D family, aimed at the next generation of ultra-low-power embedded devices.

Among the updated peripherals included on the L21 is a low-power capacitive touch-sensing controller, for touch-sensitive surfaces such as buttons, sliders or wheels. The capacitive touch peripheral can run in all low-power operating modes, and supports waking up the microcontroller from sleep when the sensors are touched.

Architectural innovations in the SAM L21 family enable low-power peripherals such as timers, serial communications and the touch controller to remain powered up and running as needed while the rest of the system is in a reduced-power sleep mode.

Nearly every peripheral system has been optimised for energy efficiency and for the ability to operate in a standalone mode without the entire chip being powered up and active. The energy-efficient L21 design goes much further than simply turning off clock distribution to the various peripheral devices on the chip when they are powered down – it completely shuts down the power to peripherals and segments of the die that are not currently in use.

The SAM L21 supports energy-efficient “sleepwalking”, which allows peripheral devices to request a clock source when they need to wake up from sleep modes and perform tasks – without having to power up the CPU, the Flash and other relatively power-intensive CPU support systems.

As an example of a real-world energy-efficient Internet-of-Things application, suppose the chip’s internal ADC is used to measure temperature in a room. You can put the CPU to sleep and wake up periodically on interrupts from the real-time clock, providing very efficient power consumption. The measured temperature can be checked against a predefined threshold to decide on further action, and if no action is required the CPU can be put back to sleep until the next interrupt is fired from the RTC at the interval desired.

During an analogue sensor read, the ADC clock will only be enabled and running when the ADC conversion is needed. When the ADC receives the trigger event from the real time clock it will request its generic clock from the generic clock controller, and this peripheral clock will stop as soon as the ADC conversion is completed.

The event system is configured to send this event from the real-time clock to the ADC, and the ADC is configured to start a conversion when it receives an event – but this is done without the need to power up the CPU at all, minimising the power budget. However, the ADC can be configured to look at its reading, check if a certain threshold is exceeded, and to generate an interrupt for a different task – waking up the CPU for example, if we decide that data logging, radio transmission or some other CPU action is needed in response to an extreme temperature value.

As with most of Atmel’s microcontroller products, Atmel is offering an Xplained Pro evaluation board for the SAM L21 microcontroller family. This evaluation board features an on-board debugger, standardised extension connectors compatible with the other expansion boards and modules in the Atmel Xplained development board ecosystem, and auto-identification in Atmel Studio.

Atmel 1

Along with the rest of Atmel’s development tools and boards, this evaluation board is powerful and flexible yet easy to use, for both professional and hobbyist-level developers.

Using the SAM L21 Xplained Pro board and Atmel Studio, designers can monitor power consumption in conjunction with the program counter in real time, and if a spike in power consumption appears you can loop back to see what’s causing it in the software and code accordingly.

Thanks to Atmel your new or existing Internet of Things devices can increase their autonomy and allow you to reduce device size and weight thanks to the use of smaller battery capacities – and of course saving you money as well. If this is of interest to you – and why wouldn’t it be – here at the LX Group we have the team, experience and technology to bring your ideas to life.

Getting started is easy – join us for an obligation-free and confidential discussion about your ideas and how we can help bring them to life – click here to contact us, or telephone 1800 810 124.

LX is an award-winning electronics design company based in Sydney, Australia. LX services include full turnkey design, electronics, hardware, software and firmware design. LX specialises in embedded systems and wireless technologies design.

Published by LX Pty Ltd for itself and the LX Group of companies, including LX Design House, LX Solutions and LX Consulting, LX Innovations.


Muhammad AwaisReduce IoT power use with Atmel SAM L21

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