# An Energy-Efficient Strategy for Microcontrollers
## 1 Introduction  
With the popularization of the concept of green computing [1], people are paying more attention to energy efficiency in computing [2]. Nowadays, large quantities of embedded systems are deployed everywhere in our daily life to satisfy the demands of modern smart life. Unlike general-purpose computing devices, embedded systems are often required to satisfy the constraint of low energy consumption. Both the operator and the users expect these devices to last longer and require little maintenance. Energy consumption has a significant impact on battery life, thermal design, device stability, and security. Additionally, energy consumption is an essential index of the performance of embedded systems. Microcontrollers provide computing and processing capability for embedded systems and have to follow energy constraints as well. [PERSON] et al. [3] pointed out that IoT processors must be optimized for energy efficiency and configurable to achieve optimal execution, especially in terms of energy efficiency. Dozens of studies about low power technology have been performed by other researchers and companies, and to reduce power consumption, many low power technologies have been proposed as well. However, because energy consumption is the integral of power over time, power is not the only impact factor in energy consumption. Although low power technology contributes greatly to reducing the power consumption of embedded microcontrollers, it also affects the performance and execution time of applications. In the field of power consumption modeling, [PERSON] et al. [4], [PERSON] et al. [5] [PERSON] et al. [6], and [PERSON] et al. [7] also mentioned that especially for mobile smart devices and IoT devices, the periods of theoperating time have a non-negligible impact on the energy consumption of embedded systems. Existing studies focused more on the impact of time overhead introduced by low-power techniques on system performance. We believe that the energy overhead of low-power techniques and the effect of time on energy consumption should be taken into consideration and analyzed when drawing up energy-saving strategies. In this paper, we reviewed some commonly used low power technologies and methods and proposed two assumptions about energy consumption. First, since energy is the integral of power over time, in some cases, energy might be saved even if instant power consumption increases. Second, the overhead introduced by processor clock frequency transitions and power mode transitions must be considered when applying dynamic voltage and frequency scaling (DVFS) and power modes. Several analytical models and a series of test sets are designed and conducted to validate our assumptions. The test results show that our assumptions are correct, and in some cases, our ideas can indeed contribute to improving energy efficiency. Based on the experiment data, we also propose several suggestions on hardware design and software development for better energy efficiency. Contributions: This research presents some contributions in the domain of improving energy efficiency of microcontrollers. 1. Analytical models are designed to analyze the effect and overhead of different low power technologies. 2. A series of tests is conducted, and the power consumption of essential peripheral components shows its impact on energy consumption. 3. A method to compare and choose the optimal among different low-power technologies is proposed to apply low-power technology more appropriately and effectively. The paper is organized as follows. Section 1 introduces the background issues of energy efficiency in embedded systems and microcontrollers. Section 2 presents the existing low-power technologies for embedded systems and microcontrollers, points out their shortcomings, and presents our ideas. Section 3 contains our analytical models corresponding to our assumptions. Section 4 contains the measuring methodology and experimental data used in the study.