Archive for November 2012

In our last post we came to know about the process of configuring the core clock for EFM32. Basically how to make the Coretx-M3 clock from the External Crystal source HFXO.
Next we would take a detailed look at the Energy modes in the EFM32 microcontroller. Again we are going to use the Keil MDK with GCC and the STK3700 kit.
In the EFM32 Microcontroller the Energy Management Unit(EMU) takes care of the setting the power, reset and clock-gating. Additionally it also takes care of Brownout detection for resetting the MCU if the voltage falls below a specified threshold to prevent spurious code execution. However we would focus more on the Energy modes that govern the operation of the Microcontroller core as well as its peripherals and clocks. This might be a bit confusing that CMU is responsible for clock then why EMU. Yes, the CMU is for conguration of the clocks, clock-gating and dividers, but the oscillator control also has additional parameters that are decided by the EMU. We would cone to clarity on this soon.

We have been doing quite a bit of development on low power Cortex-M3 microcontrollers. There were many nice lessons in low power design that we learned on our way. We would like to share this as a series of articles to helpful for making energy efficient designs.

We are really impressed by the low power features of EFM32 and wish to share a step by step guide in order to finally make a complete system that is more power efficient without compromising on the performance.
 One of the key components of a Microcontroller based system is the clock. This would ultimately decide the amount of switching that would take place inside the microcontroller. Finally the performance through put of the Cortex-M3 is again dependent on the clock, although not completely.
Thus the first and most important thing in a low power design would be to design the clocks properly and make sure that unused logic on the microcontroller is "clock-gated" when not in use. The term "clock-gating" means that we would prevent the clock from entering a particular peripheral or bus or even the CPU core when its not being used. The reduction in the spurious clock to unused peripherals would result in significant reduction in power consumption due to reduced switching losses.

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