Abstract
Energy harvesting sensor systems typically incorporate energy buffers (e.g., rechargeable batteries and supercapacitors) to accommodate fluctuations in supply. However, the presence of these elements limits the miniaturization of devices. In recent years, researchers have proposed a new paradigm, transient computing, where systems operate directly from the energy harvesting source and allow computation to span across power cycles, without adding energy buffers. Various transient computing approaches have addressed the challenge of power intermittency by retaining the processor’s state using non-volatile memory. However, no generic approach has yet been proposed to retain the state of peripherals external to the processing element. This paper proposes RESTOP, flexible middleware which retains the state of multiple external peripherals that are connected to a computing element (i.e., a microcontroller) through protocols such as SPI or IC. RESTOP acts as an interface between the main application and the peripheral, which keeps a record, at run-time, of the transmitted data in order to restore peripheral configuration after a power interruption. RESTOP is practically implemented and validated using three digitally interfaced peripherals, successfully restoring their configuration after power interruptions, imposing a maximum time overhead of 15% when configuring a peripheral. However, this represents an overhead of only 0.82% during complete execution of our typical sensing application, which is substantially lower than existing approaches.
Highlights
Energy harvesting (EH) potentially enables the long-term deployment of low-power sensor systems without the need to replace batteries
We have proposed RESTOP, a new approach to retain the state of peripherals that communicate with an microcontroller unit (MCU) through a digital interface, in transient computing systems
The presented middleware provides generic functions to read data from the external peripherals or write to them, and keeps track of and saves the transmitted configuration data into the instruction history table from where the peripheral state is restored after a power failure
Summary
Energy harvesting (EH) potentially enables the long-term deployment of low-power sensor systems without the need to replace batteries. EH sources are usually intermittent and unpredictable because they depend on external conditions (i.e., availability of energy to be harvested) [1]. To overcome this limitation, systems typically integrate energy storage devices (e.g., supercapacitors or rechargeable batteries) to smooth out supply variations. Systems typically integrate energy storage devices (e.g., supercapacitors or rechargeable batteries) to smooth out supply variations This approach is known as energy-neutral operation, where energy storage is used to balance the stored energy with the long-term energy consumed and, sustain operation during power shortages [2]. Transient computing (Figure 1b) aims to power systems directly from the EH source, operating when energy is available and retaining system state during supply interruptions
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