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  1. Free, publicly-accessible full text available January 1, 2024
  2. Free, publicly-accessible full text available January 1, 2024
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  4. Information is an integral part of the correct and reliable operation of today's computing systems. Data either stored or provided as input to computation processing modules must be tolerant to many externally and internally induced destructive phenomena such as soft errors and faults, often of a transient nature but also in large numbers, thus causing catastrophic system failures. Together with error tolerance, reliable operation must be provided by reducing the large overheads often encountered at system-level when employing redundancy. While information-based techniques can also be used in some of these schemes, the complexity and limited capabilities for implementing high order correction functions for decoding limit their application due to poor performance; therefore, N Modular Redundancy (NMR) is often employed. In NMR the correct output is given by majority voting among the N input copies of data. Reduced Precision Redundancy (RPR) has been advocated to reduce the redundancy, mostly for the case of N = 3; in a 3RPR scheme, one full precision (FP) input is needed while two inputs require reduced precision (RP) (usually by truncating some of the least significant bits (LSBs) in the input data). However, its decision logic is more complex than a 3MR scheme. This paper proposes a novel NRPR scheme with a simple comparison-based approach; the realistic case of N = 5 is considered as an example to explain in detail such proposed scheme; different arrangements for the redundancy (with three or four FP data copies) are considered. In addition to the design of the decision circuit, a probabilistic analysis is also pursued to determine the conditions by which RPR data is provided as output; it is shown that its probability is very small. Different applications of the proposed NRPR system are presented; in these applications, data is used either as memory output and/or for computing the discrete cosine transform. In both cases, the proposed 5RPR scheme shows considerable advantages in terms of redundancy management and reliable image processing. 
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  5. Approximate communication is being seriously considered as an effective technique for reducing power consumption and improving the communication efficiency of network-on-chips (NoCs). A major problem faced by these techniques is quality control: how do we ensure that the network will transmit data with sufficient accuracy for applications to produce acceptable results? Previous methods that addressed this issue require each application to calculate the approximation level for every piece of approximable data, which takes hundreds of cycles. So the approximation information is often not available when a request packet is transmitted. Therefore, the reply packet with the approximable data is transmitted with unnecessarily absolute accuracy, reducing the effectiveness of approximate communication. In this paper, we propose a hardware-based quality management framework for approximate communication to minimize the time needed for the approximation level calculation. The proposed framework employs a configuration algorithm to continuously adjust the quality of every piece of data based on the difference between the output quality and the application's quality requirement. When the proposed framework is implemented in a network, every request packet can be transmitted with the updated approximation level. This framework results in fewer flits in each data packet and reduces traffic in NoCs while meeting the quality requirements of applications. Our cycle-accurate simulation using the AxBench benchmark suite shows that the proposed online quality management framework can reduce network latency by up to 52% and dynamic power consumption by 59% compared to previous approximate communication techniques while ensuring 95% output quality. This hardware-software codesign incurs 1% area overhead over previous techniques. 
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