| Resumo: | As the number of connected things increases at a very fast pace, the Internet of Things (IoT) ecosystem expands and nowadays covers a vast number of application domains, providing a large portfolio of solutions that are based on an evolving system, from the physical sensors (end devices) to the Cloud. When designing battery-powered end devices, previous research has identified several challenges such as wireless connectivity, battery lifetime, embedded intelligence, security and privacy concerns, and costs (modem unit, communication link and maintenance, among others). This paper focuses on the design and development of battery-powered IoT devices in which NarrowBand Internet of Things (NB-IoT) is used to provide seamless wireless connection, reduce power consumption, enhance communication coverage and minimize maintenance costs. The paper describes a typical use case where an Arm Cortex -M0+ and its low-power modes are exploited in order to design a low-power end device. Two different approaches, bare-metal and freeRTOS, for implementing the end device firmware are compared. Additionally, performance tests prove that increasing the clock frequency of the processor does not bring any advantage to this kind of applications. ® ®
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