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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® microcontroller employs 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 architecture, 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 an Atmel AVR microcontroller.
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 AVR 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 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 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.
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 AVR microcontroller's low-power features to be used even more often.
Designed for low power
The essence of an AVR picoPower device goes beyond merely the various picoPower features included in an AVR device. The design methodology, the process geometry, and even the kinds of transistors used are all essential power-saving parts of an AVR picoPower device. All AVR 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 all sleep modes.
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 AVR picoPower technology are carefully designed analog functions that continue to operate all the way down to 1.62V.
Traditionally, the 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 prevents 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 AVR 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, and so running at as low a supply voltage as possible saves power. For battery operated devices, the Atmel AVR microcontroller can make use of the remaining power available at lower battery voltage levels as the battery depletes.
As part of the AVR picoPower technology, Atmel has added intelligence to the AVR 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 false CPU wakeups.
In the traditional way of addressing this, the 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.
The Atmel AVR microcontroller solves this problem with its 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 true.
SleepWalking is only one of the many innovative technologies found in all Atmel AVR 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.
The Atmel AVR microcontroller can wake up from sleep mode in 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 microcontroller spends less time waking up so the total power consumed is put to the best possible use.