Time synchronisation is crucial for distributed systems, and particularly for Wireless Sensor Networks (WSNs), where each node is executing concurrent operations to achieve a real-time objective. However, synchronisation is quite difficult to achieve in WSNs, due to the unpredictable deployment conditions and to physical effects like thermal stress, that cause drifts in the local node clocks. As a result, state-of-the-art synchronisation schemes do not guarantee monotonicity of the nodes clock, or are relying on external hardware assistance. In this paper we present FLOPSYNC-2, a scheme to synchronise the clocks of multiple nodes in a WSN, requiring no additional hardware, and based on the application of control-theoretical principles. The scheme guarantees low overhead, low power consumption and synchronisation with clock monotonicity.We propose an implementation of FLOPSYNC-2 on top of the microcontroller operating system Miosix, and prove the validity of our claims with several-days-long experiments on an eight-hop network. The experimental results show that the average clock difference among nodes is limited to a hundred of ns, with a sub-μs standard deviation. By introducing a suitable power model, we also prove that synchronisation is achieved with a sub-μA consumption overhead.

Clock synchronization is a necessary component in modern distributed systems, especially Wireless Sensor Networks (WSNs). Despite the great effort and the numerous improvements, the existing synchronization schemes do not yet address the cancellation of propagation delays. Up to a few years ago, this was not perceived as a problem, because the time-stamping precision was a more limiting factor for the accuracy achievable with a synchronization scheme. However, the recent introduction of efficient flooding schemes based on constructive interference has greatly improved the achievable\ud accuracy, to the point where propagation delays can effectively become the main source of error.\ud In this paper, we propose a method to estimate and compensate for the network propagation delays. Our proposal does not require to maintain a spanning tree of the network, and exploits constructive interference even to transmit packets whose content are slightly different. To show the validity of the approach, we implemented the propagation delay estimator on top of the FLOPSYNC-2 synchronization scheme. Experimental results prove the feasibility of measuring propagation delays using off-the-shelf microcontrollers and radio transceivers, and show how the proposed solution allows to achieve sub-microsecond\ud clock synchronization even for networks where propagation delays are significant

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Architectures targeted at embedded systems often have limited floating point computation capabilities, and in many cases do not provide any hardware support. In this work, we propose a self-contained compiler transformation pass implemented within LLVM to perform floating point to fixed point conversion. This pass is used to optimize the scheduler of the MIOSIX 1 embedded real-time operating system. We compare the proposed approach with the original floating point implementation, a handtuned fixed point one, and a solution based on a C++ library for fixed-point arithmetic. Our solution achieves speedups with respect to original floating point implementation up to 3.1 ×.

This manuscript proposes a novel viewpoint on computing systems' modelling. The classical approach is to consider fully functional systems and model them, aiming at closing some external loops to optimize their behaviour. On the contrary, we only model strictly physical phenomena, and realize the rest of the system as a set of controllers. Such an approach permits rigorous assessment of the obtained behaviour in mathematical terms, which is hardly possible with the heuristic design techniques, that were mainly adopted to date. The proposed approach is shown at work with three relevant case studies, so that a significant generality can be inferred from it.

Collecting vast amount of data and performing complex calculations to feed modern Numerical Weather Prediction (NWP) algorithms require to centralize intelligence into some of the most powerful energy and resource hungry supercomputers in the world. This is due to the chaotic complex nature of the atmosphere which interpretation require virtually unlimited computing and storage resources. With Machine Learning (ML) techniques, a statistical approach can be designed in order to perform weather forecasting activity. Moreover, the recently growing interest in Edge Computing Tiny Intelligent architectures is proposing a shift towards the deployment of ML algorithms on Tiny Embedded Systems (ES). This paper describes how Deep but Tiny Neural Networks (DTNN) can be designed to be parsimonious and can be automatically converted into a STM32 microcontroller-optimized C-library through X-CUBE-AI toolchain; we propose the integration of the obtained library with Miosix, a Real Time Operating System (RTOS) tailored for resource constrained and tiny processors, which is an enabling factor for system scalability and multi tasking. With our experiments we demonstrate that it is possible to deploy a DTNN, with a FLASH and RAM occupation of 45,5 KByte and 480 Byte respectively, for atmospheric pressure forecasting in an affordable cost effective system. We deployed the system in a real context, obtaining the same prediction quality as the same DNN model deployed on the cloud but with the advantage of processing all the necessary data to perform the prediction close to environmental sensors, avoiding raw data traffic to the cloud.

The density of modern microprocessors is so high, that operating all their units at full power would destroy them by thermal runaway. Hence, thermal control is vital, but at the same time has to integrate with power/performance management, to not unduly limit computational speed. In addition, the controller must be simple and computationally light, as millisecond-scale response is required. Finally, since microprocessors face a variety of operating conditions, postsilicon tuning is an issue. We here present a solution, by exploiting event-based control and a hardware/software partition to maximize efficiency, lightness, and flexibility. We show experiments on real hardware, evidencing the obtained advantages over the state of the art