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Embedded Design Blog
Multiple clock domains
It is well known that microcontrollers can be run at different speeds. And it is equally well known that as you lower the frequency, less power is used. When designing a product for lowest possible system power, it does not make sense to clock every part of a microcontroller at the same frequency.
The Atmel® AVR® and Atmel® ǀ SMART ARM®-based microcontrollers employ multiple clock domains to enable different parts of the microcontroller—the core, the internal buses, and the individual peripherals—to be individually clocked to save power. If the maximum throughput of a peripheral is not needed in an application, the clock can be lowered. Individual clocks can be applied to different peripherals so they can be fully optimized with power consumption in mind. The throughput or feature requirement of the application is still fulfilled while power consumption is lowered.
It's one thing to be able to scale the clocks individually. But with the AVR and SMART architectures, unused peripherals can also be fully shut down individually and enabled again during runtime, further lowering power consumption without compromising system operation. Multiple clock domains allow an application to be optimized for performance and power at the same time. Just as expected from Atmel AVR® and Atmel ǀ SMART microcontrollers.
DMA controller and event system
Moving data to or from a peripheral or memory has traditionally been a task for the CPU. The more data there is to move from A to B, the more CPU cycles are needed to move it. But there are alternatives. With Atmel picoPower® technology, a direct memory access (DMA) controller can perform this task much more energy efficiently by allowing the CPU to sleep and conserve power.
With the DMA controller, data in an Atmel AVR or Atmel ǀ SMART microcontroller can be moved from A to B without involving the CPU at all. The CPU can be put into a sleep mode while the data is being moved to save power or used for other tasks such as computations. This results in a higher system performance, and allows the microcontroller to go into a sleep mode more often to save more power.
The Atmel AVR® or Atmel ǀ SMART microcontroller’s Event System allows peripherals to make intelligent decisions and pass data directly to other peripherals. A dedicated routing network is used to transmit the data, and it is totally independent of the CPU. This network offloads the CPU and can be utilized in sleep modes. System performance is increased while power consumption is lowered. In addition, it is 100 percent deterministic and perfectly suited for real-time applications.
The DMA controller can reduce system power even further by using a hardware CRC engine to automatically calculate a checksum to provide integrity checking and save additional CPU power consumption on wakeup. With the DMA controller and Event System, less time is spent moving data and more time can be spent in sleep mode, enabling the Atmel | SMART AVR microcontroller's low-power features to be used even more often.
Designed for low power
The essence of an Atmel picoPower device goes beyond merely the various picoPower features included. The design methodology, the process geometry, and even the types of transistors used are all essential power-saving parts of an Atmel picoPower device. All picoPower devices are designed from the ground up for low power consumption utilizing Atmel’s proprietary low leakage processes and libraries to provide industry leading low power consumption in active and all sleep modes.
To improve the ease of use for software developers, Atmel introduced several new low-power features available on different low-power microcontrollers:
- On-the-fly user selectable performance levels
- Automatic voltage regulator switching with multiple operating modes
- Multiple power domains with automatic power domain gating
- Automatic low power SRAM switching with optional disable
- Low power battery backup mode
To enable developers to balance between performance and power consumption, low-power devices offer on-the-fly user selectable performance levels. These performance levels allow the user to scale to the lowest core voltage level that will support a given operating frequency.
Atmel’s low-power devices have internal voltage regulators with different operating modes that can be manually adjusted by the user or handled automatically depending on the performance level, sleep mode selected, or SleepWalking™ status. Below is an illustration of automatic voltage regulator switching between different sleep modes.
Multiple power domains are offered to allow automatic and user control of power to different peripherals and system features. Automatic power domain gating consists of turning on or off different power domain voltages to save power while keeping required power domains active. When a power domain is disabled through automatic power domain gating, the logic state of all peripherals and is retained and the process is completely transparent to the application/user, but minimizes the static power consumption.
picoPower devices offer a variety of low-power SRAM options including automatic switching to low-power mode during sleep and selectable disabling of portions of the SRAM in deep sleep modes.
Another feature available in select picoPower devices is the battery backup sleep mode. In this mode, all peripherals, memory, clocks, and oscillators are powered off and only the backup domain remains active. The backup domain consists of the RTC, 32KHz clock sources, and wake-up from external pins.
True 1.62V operation
An easy way to reduce power consumption in any design is to lower the operating voltage. But this would be mostly useless if analog performance was compromised. Central to the picoPower technology are carefully designed analog functions that continue to operate all the way down to 1.62V.
Traditionally, various features of a microcontroller become unstable or even unusable at different voltage levels. Inaccuracies in analog peripherals, limited operation or an inability to write to non-volatile memory prevent designs from running at lower voltages. This leads to shorter battery life, larger and more expensive batteries, or a lot time spent trying to find workarounds for something that should be addressed by the microcontroller to begin with.
Atmel picoPower microcontrollers offer true 1.62 V operation, including all analog modules, oscillators, and flash and EEPROM programming. So what does this mean in practice? It means different microcontroller features will not shut down one by one as the voltage drops. You can run the same application at different voltages without making comprises. All peripherals are available regardless of supply voltage. The ADC, for example, can be used to measure the supply voltage as the cutoff voltage is approached, and when detected, it enables the application to store vital information and ensure a safe shutdown, enabling a glitch-free restart after changing batteries.
Power consumption is proportional to supply voltage, so running at as low a supply voltage as possible saves power. For battery operated devices, the Atmel microcontrollers can make use of the remaining power available at lower battery voltage levels as the battery depletes.
As part of the picoPower technology, Atmel has added intelligence to the peripherals. This allows a peripheral to determine if incoming data requires use of the CPU or not. We call this SleepWalking™ because it allows the CPU to sleep peacefully until an important event occurs, eliminating millions of unnecessary CPU wakeups.
In the traditional way of monitoring the world outside the device, an internal timer wakes up the microcontroller periodically to check whether certain conditions that require its attention are present or not. The CPU and RAM traditionally consume the majority of the power in active mode, and so waking up the CPU to check for these conditions will consume a lot of power in the long run. In some cases where the reaction time is too short, it might not even be possible for the CPU to go back into sleep mode at all.
Atmel AVR® and Atmel ǀ SMART microcontrollers solve this problem through SleepWalking peripherals. SleepWalking allows the microcontroller to be put into deep sleep and wake up only upon a pre-qualified event. The CPU no longer needs to check whether or not a specific condition is present, such as an address match condition on the TWI (I2C) interface, or a sensor connected to an ADC that has exceeded a specific threshold. With SleepWalking, this is done entirely by the peripherals themselves. The CPU and RAM will not wake up until the condition is true.
This allows huge savings in system power consumption for many applications. SleepWalking enables a hardware Peripheral Touch Controller to wake a system on touch or proximity, allowing the use of capacitive touch power buttons in battery powered applications. SleepWalking supports analog signal acquisition and measurement through integrated op-amps or ADCs while the CPU idles, greatly extending battery life for analog and digital sensor applications. Serial communications and DMA transfers can use SleepWalking to enable communication and dataflow from ultra low power modes. User-configurable combinatorial and sequential logic blocks – available in many picoPower devices – can even be combined with SleepWalking to combine and filter out signals to prevent even more unnecessary CPU wake-ups. Any power sensitive application – from wearable medical sensors to portable gas detectors to wireless communication modules – will reduce system power consumption by using Atmel SleepWalking technology.
Dynamic sleepwalking optimizes power consumption even further by enabling power domain transitions without waking the CPU. This allows the MCU to standby in the lowest possible power mode, autonomously increase to a higher power domain if required to use additional system or peripheral resources, and return to low power mode once the event has been handled.
SleepWalking is only one of the many innovative technologies found in Atmel AVR and Atmel ǀ SMART microcontrollers that reduce total system power consumption in your application.
Entering a sleep mode shuts down parts of the microcontroller to save power. Oscillators and clocks can consume a considerable amount of power when in use, and when waking up from sleep modes, these clocks need to be stable before they can be used. Waiting a long time for the clocks to be available and stable will result in wasted power.
Atmel AVR and Atmel ǀ SMART microcontrollers were designed to wake up extremely fast – in as little as eight clock cycles when running from the internal RC oscillator. In addition, a digital frequency locked loop (DFLL) replaces the traditional phase locked loop (PLL) to provide a programmable internal oscillator that is much faster and more accurate. It can also eliminate external components, which reduces the total system power consumption even more. When in sleep mode with the synchronous clocks turned off, the microcontroller can still wake up from asynchronous events such as a pin change, data received or even an I2C bus address match, enabling multiple wake-up sources from even the deepest sleep modes. The Atmel AVR and Atmel ǀ SMART microcontrollers spend less time waking up so the total power consumed is put to the best possible use.
Atmel® ǀ SMART ARM®-based MCUs
- SAM L21 – ARM Cortex®-M0+ based MCU delivers low power consumption down to 35 µA/MHz in active move along with AES, capacitive touch sensing, and full-speed USB device and host.
- SAM L22 – ARM Cortex®-M0+ based MCU with Segment LCD (SLCD) controller delivers low power consumption down to 39 µA/MHz in active move along with AES, capacitive touch sensing, tamper detection and full-speed USB device.
- SAM4L – ARM Cortex-M4 based MCU delivers down to 90µA/MHz in active mode while providing power signal processing and high-speed communication peripherals.
Atmel AVR® MCUs
- XMEGA – All Atmel XMEGA MCUs feature picoPower technology and deliver high performance, secure, and low power consumption in an 8-bit package.
» See the full portfolio
- megaAVR – Widest selection of devices for memory size, pin-count, and peripheral options with innovative picoPower to reduce power consumption.
- ATmega168PB 8-bit AVR Microcontroller, 16KB Flash, 32-pin
- ATmega48P 8-bit picoPower AVR Microcontroller, 4KB Flash, 28/32-pin
- ATmega48PA 8-bit picoPower AVR Microcontroller, 8KB Flash, 28/32-pin
- All megaAVR devices with a "P" at the end of the device name will feature the picoPower technology
» See the full portfolio
- tinyAVR – Offers unrivalled combination of miniaturization, processing power, analog performance and system-level integration all with highly optimized power efficiency.