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SAM4L Cortex-M4 Low Power Microcontroller Slide 10
The Event System supports asynchronous events in addition to standard synchronous events. Asynchronous events can even be processed in various sleep modes with no running system clock. This is accomplished by taking advantage of some Advanced Power Manager features such as Sleep Walking and Asynchronous Wakeup. Sleep Walking allows the Event System to handle asynchronous events in various sleep modes by requesting a module local clock for the duration of the Event processing. When the event processing is done, the clock request is disserted and the module goes back to sleep. Let’s take a monitoring example, the old way: you want to monitor some analog input signal. If the analog input is below a certain value, do nothing, if not, do something else. The RTC would wake the system and the core at regular intervals; the sampling frequency. The core would then do the measurement and address the value and take appropriate action. If you look at microcontroller power consumption; the core and RAM will consume up to 70% in active mode. And in most cases, you can assume that no action will be taken after measuring the ADC. That is a lot of wasted power. With SleepWalking; the peripheral can choose to wake up the system when the event is qualified at a peripheral level. The device is in deep sleep mode and is woken up by an RTC interrupt. The ADC makes a measure and compares it to the user set threshold. The temperature is checked and is found to be below the threshold and the device goes down to deep sleep again. When the next RTC interrupt is triggered, the ADC is woken up again. This time around, the value is above the threshold. Now the event is qualified and the CPU and RAM will be woken up. The event is qualified at a peripheral level and only when needed, the CPU and RAM is woken up.
PTM Published on: 2013-01-23