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SAM4L Cortex-M4 Low Power Microcontroller Slide 9
The Event System allows peripherals to communicate directly without involving the CPU. It is a routing network independent of the traditional data paths like buses, for instance. Different triggers can be at the peripheral level that would result in an event; like a data transfer to another peripheral. So in many ways it is an extension to DMA with the possibility to make decisions. This is without using the CPU. The event system has a fixed latency of two cycles. Without any jitter it is predictable and a perfect fit for real-time applications. No events are lost and they are handled at a peripheral level. The traditional way of handling data or actions for a power limited application is through the use of interrupts. An interrupt would wake up the CPU requesting a data transfer, and action or computation. For instance, say the designer is driving a motor with PWM and they want the motor to run at a steady pace. At regular intervals the PWM period would be slightly adjusted to make sure the motor ran at the same RPMs. An interrupt would wake the CPU at a regular basis and the CPU would have to get the current speed from the ADC, compare it with the offset and then adjust the PWM period before the CPU could go back to sleep. The Event System automates this; An RTC event can wake the ADC and request a conversion. The ADC will send an event to the analog comparator requesting that a comparison between the current speed and the set threshold. In turn the analog comparator would send an action to the PWM to increase or decrease the period. This is achieved completely without using the CPU.
PTM Published on: 2013-01-23