Heterogeneous MPSoCs designed for non-safety-critical embedded applications (e.g, streaming applications) may allow a (limited) presence of errors in the application results before detection and confinement are effected. In turn, this allows to reduce the massive redundancy required to achieve fully concurrent error detection, reaching a balance between time elapsed before errors are detected and introduced area/power overhead. We envision in this paper the adoption of a modified semi-concurrent online checking approach that uses deferred time-multiplexed software emulation of redundant tasks on the available hardware platform rather than straightforward hardware redundancy. Our approach reduces the amount of redundancy requested by previous self-checking approaches and allows greater flexibility of operation; rigidly synchronous operation of units concurring in a checking action at any given time is avoided, introducing a delayed checking solution.

As the complexity of designs increases and technology scales down into the deep-submicron domain, the probability of malfunctions and failures in the networks-on-chip (NoCs) components increases. In this work, we focus on the study and evaluation of techniques for increasing reliability and resilience of network interfaces (NIs) within NoC-based multiprocessor system-on-chip architectures. NIs act as interfaces between intellectual property cores and the communication infrastructure; the faulty behavior of one of them could affect, therefore, the overall system. In this work, we propose a functional fault model for the NI components by evaluating their susceptibility to faults. We present a two-level fault-tolerant solution that can be employed for mitigating the effects of both permanent and temporary faults in the NI. Experimental simulations show that with a limited overhead, we can obtain an NI reliability comparable to the one obtainable by implementing the system by using standard triple modular redundancy techniques, while saving up to 48 percent in area, as well as obtaining a significant energy reduction.

Modern embedded systems increasingly require adaptive run-time management. The system may adapt the mapping of the applications in order to accommodate the current workload conditions, to balance load for efficient resource utilization, to meet quality of service agreements, to avoid thermal hot-spots and to reduce power consumption. As the possibility of experiencing run-time faults becomes increasingly relevant with deep-sub-micron technology nodes, in the scope of the MADNESS project, we focus particularly on the problem of graceful degradation by dynamic remapping in presence of run-time faults. In this paper, we summarize the major results achieved in the MADNESS project until now regarding the system adaptivity and fault tolerant processing. We report the first results of the integration between platform level and middleware level support for adaptivity and fault tolerance. A case study demonstrates the survival ability of the system via a low-overhead process migration mechanism and a near-optimal online remapping heuristic.

Networks-on-Chip (NoCs) appeared as a strategy to deal with the communication requirements of complex IP-based System-on-Chips. As the complexity of designs increases and the technology scales down into the deep-submicron domain, the probability of malfunctions and failures in the NoC components increases. This paper focuses on the study and evaluation of techniques for increasing reliability and resilience of Network Interfaces (NIs). NIs act as interfaces between IP cores and the communication infrastructure, a faulty behavior in them could affect therefore the overall system. In this work, we propose a functional fault model for the NI components, and we present a two-level fault tolerant solution that can be employed for mitigating the effects of both single-event upset soft errors and hard errors on the NI. Experiments show that with a limited overhead we can obtain a significant reliability of the NI, while saving up to 83% in area with respect to a standard Triple Modular Redundancy implementation, as well as a significant energy reduction.

Automatic generation of code starting from lightweight modeling languages such as UML is by now a widely adopted approach. In particular generation of executable SystemC models starting from StateCharts and other UML diagrams represents a promising research field. While RTL SystemC appears better suited for matching the StateCharts formalism (being intrinsically clocked), performances of the generated code suffer from the heavy overhead induced by time management, specially when the number of concurrent processes is high. In this paper we present a methodology that allows applying a solution mixing event based and clock-driven approach. More specifically, clock-driven simulation is activated only when the configuration of the system is identified to be evolving. When no events are present this fact is also detected (together with the interval of absence of events) so that no simulation is performed although the clock runs on. This solution is particularly suited for low duty cycle systems, as, e.g. when simulating Wireless Sensor Networks (WSN); in such instances, speedup of the generated code has been found to be well over two orders of magnitude. Application of the technique to the generation of a power simulator for the IEEE 802.15.4 networking protocol is used as a test case.

is a recent low-rate/low-power standard for wireless personal area and sensor networks. Its simple infrastructure, intermediate range and good power performance make it a candidate for applications that require a reasonably low throughput but a very high device lifetime and power efficiency. An experimental power analysis of an 802.15.4 implementation is carried out, providing a detailed power model of the protocol based on concurrent state machines; resulting power model is then used to generate a customized simulator. The model has been validated through a set of experiments and provides good accuracy; results are discussed, considering in particular use of the model as a basis for subsequent optimizations on 802.15.4 networks.

Security has gained increasing relevance in the development of embedded devices. Towards the aim of a secure system at each level of the design, in this paper we address security aspects related to networks-on-chips (NoCs) architectures. After presenting the attacks most likely to address NoCs, we survey existing academic and industrial secure architectures relevant to our case, focusing in particular on their communication infrastructure. We outline and propose possible solutions to contrast some of the attacks described and suggest the use of the NoC as a mean to monitor and detect unexpected system behaviors.

In this paper we present a tool that converts specifications written with a subset of StateCharts into SystemC behavioral models. The main advantages of such an approachare rapidity of use, simplicity and reusability. Various systems can be modeled at different levels of abstraction andaccuracy through StateCharts and different peculiar aspects (e.g. energy, performances) can be taken into consideration. Moreover different parts of the design can be identified at different detail levels. The kernel of the simulator is fully discussed together with its mapping to the semantics of our StateCharts diagrams. As a case study we present here a model of the IBM PowerPC 750 Cache system and the respective SystemC simulator automatically generated by our tool.

Instruction level parallelism (ILP) extraction for multicluster VLIW processors is a very hard task. In this paper, we propose a retargetable architecture that can exploit ILP and thread level parallelism jointly, thus allowing an easier parallelism extraction and improving the performance with respect to traditional multicluster VLIW processors.

Battery-powered mobile devices featuring wireless connectivity are becoming part of everyday life. In a functional breakdown of their power budget, communication accounts for a steadily increasing share of the total power; this is pushing research on power management of the wireless interfaces. The key to effective power management is power modeling. We describe a power modeling methodology featuring variable granularity and low computational burden, which can be applied to any wireless protocol. We apply it to Bluetooth and model two different BT modules, highlighting how different power management policies suit different implementations.

Main goal of the paper is introducing a dynamic branch prediction scheme suitable for energy-aware VLIW (Very Long Instruction Word) processors. The proposed technique is based on a compiler hint mechanism to filter the accesses to the branch predictor blocks. Experimental results have been carried out on Lx/ST200, an industrial 4-issue VLIW architecture. We gathered two sets of results: First, by introducing the proposed low-power branch prediction technique in the Lx processor, which features fully static branch prediction, a significant improvement of the energy-delay metric has been observed. Second, we evaluated filtering efficacy of the proposed method and we found that it gets an access reduction to the branch prediction unit of 93% with respect to a processor directly derived from Lx, featuring cycle-by-cycle prediction, corresponding to an average 9% energy reduction of the whole processor power budget.

The proliferation of pervasive computing applications relying on battery--powered devices and wireless connectivity is posing great emphasis on the issue of power optimization. While node--level models and approaches have been widely discussed, a problem requiring even greater attention is that of power associated with the communication protocols. We propose a high--level modeling methodology based on Finite State Machines useful to predict the energy consumption of given communication tasks with very low computational cost, which can be applied to any protocol. We use this methodology to create a power model of Bluetooth that we characterize and validate experimentally on a real implementation.

Main goal of the paper is to introduce a branch prediction scheme suitable for energy-efficient VLIW (Very Long Instruction Word) processors aiming at reducing the energy associated with the prediction phase by filtering the accesses to the branch predictor block. To analyze the effectiveness of the proposed low-power branch prediction scheme, we combined it to some well-known dynamic branch prediction techniques suitable for VLIW processors. Experimental results have been carried out on Lx, a 4-issue VLIW architecture with 6-stage pipeline. The proposed solution implies a performance improvement of 7% on average and an average energy reduction of 15%.

Aim of this paper is to propose a methodology for the definition of an instruction-level energy estimation framework for VLIW (Very Long Instruction Word) processors. The power modeling methodology is the key issue to define an effective energy-aware software optimisation strategy for state-of-the-art ILP (Instruction Level Parallelism) processors. The methodology is based on an energy model for VLIW processors that exploits instruction clustering to achieve an efficient and fine grained energy estimation. The approach aims at reducing the complexity of the characterization problem for VLIW processors from exponential, with respect to the number of parallel operations in the same very long instruction, to quadratic, with respect to the number of instruction clusters. Furthermore, the paper proposes a spatial scheduling algorithm based on a low-power reordering of the parallel operations within the same long instruction. Experimental results have been carried out on the Lx processor, a 4-issue VLIW core jointly designed by HPLabs and STMicroelectronics. The results have shown an average error of 1.9% between the cluster-based estimation model and the reference design, with a standard deviation of 5.8%. For the Lx architecture, the spatial instruction scheduling algorithm provides an average energy saving of 12%.

Summary form only given. The overall goal of this work is to define an instruction-level power macro-modeling and characterization methodology for VLIW embedded processor cores. The approach presented in this paper is a major extension of the work previously proposed, targeting an instruction-level energy model to evaluate the energy consumption associated with a program execution on a pipelined VLIW core. Our ongoing work aims at defining a power optimization technique based on the proposed model. The technique consists of a spatial rescheduling of the operations within the same long instruction to reduce their instruction power overhead.

We propose a retargetable architecture, based on a multicluster VLIW processor that can exploit either instruction level parallelism (ILP) or ILP and data level parallelism (DLP) jointly in a SIMD fashion. Simulation results show that performances may increase significantly when the application is compiled for the proposed architecture.

In this paper, an instruction-level energy model is proposed for the data-path of very long instruction word (VLIW) pipelined processors that can be used to provide accurate power consumption information during either an instruction-level simulation or power-oriented scheduling at compile time. The analytical model takes into account several software-level parameters (such as instruction ordering, pipeline stall probability, and instruction cache miss probability) as well as microarchitectural-level ones (such as pipeline stage power consumption per instruction) providing an efficient pipeline-aware instruction-level power estimation, whose accuracy is very close to those given by RT or gate-level simulations. The problem of instruction-level power characterization of a K-issue VLIW processor is O(N/sup 2K/) where N is the number of operations in the ISA and K is the number of parallel instructions composing the very long instruction. One of the advantages of the proposed model consists of reducing the complexity of the characterization problem to O(K/spl times/N/sup 2/). The proposed model has been used to characterize a four-issue VLIW core with a six-stage pipeline.

Proposes a low-power approach to the design of embedded very long instruction word (VLIW) processor architectures based on the forwarding (or bypassing) hardware, which provides operands from interstage pipeline registers directly to the inputs of the function units. The power optimization technique exploits the forwarding paths to avoid the power cost of writing/reading short-lived variables to/from the register file (RF). Such optimization is justified by the fact that, in application-specific embedded systems, a significant number of variables are short-lived, that is, their liveness (from first definition to last use) spans only few instructions. Values of short-lived variables can thus be accessed directly through the forwarding registers, avoiding writeback to the RF by the producer instruction and successive read from the RF by the consumer instruction. The decision concerning the enabling of the RF writeback phase is taken at compile time by the compiler static scheduling algorithm. This approach implies a minimal overhead on the complexity of the processor control logic and, thus, no critical path increase. The application of the proposed solution to a VLIW embedded core has shown an average RF power saving of 7.8% with respect to the unoptimized approach on the given set of target benchmarks.

In this paper, a low-power approach to the design of embedded VLIW processor architectures is proposed. To solve the most part of data hazards in the pipeline, processors use forwarding (or bypassing) hardware to provide the required operands from the inter-stage pipeline registers directly to the inputs of the function units. The operands are then stored in the register file during the write-back pipeline stage. In this paper, we propose a power optimization technique based on the exploitation of the forwarding paths in the processor to avoid the power cost of writing/reading short-lived variables to/from the register file. In application-specific embedded systems, experimental evidence has shown that a significant number of variables are short-lived, that is their liveness (front first definition to last use) spans only few instructions. Values of short-lived variables can be accessed directly through the forwarding registers, avoiding write-back. An application example of our solution to a VLIW embedded core, when accessing the register file, has shown a power saving up to 35% with respect to the unoptimized approach on the given set of target benchmarks. The performance overhead is equal to one-gate delay to be added on the processor critical-path.

A high-level synthesis strategy is proposed for design of semiconcurrently self-checking devices. Attention is mainly focused on data path design. After identifying the reference architecture against which cost and performance are evaluated, a simultaneous scheduling-and-allocation strategy is presented for linear-code data flow graphs, allowing resource sharing between nominal and checking data paths. The proposed strategy is actually independent from a specific scheduling-and-allocation algorithm since it is essentially concerned with the introduction of the fault tolerance issue at high-abstraction level in any design environment. Conventional duplication with comparison, even if considered in a high-level synthesis strategy, leads to high circuit complexity increase. The proposed approach provides that the required checking periodicity is satisfied while minimizing additional functional units by means of maximum reuse of the resources available for the nominal computation as long as error detection ability is preserved. The strategy is then extended to deal with branches and loops in the data path. Risk of error aliasing due to resource sharing is analyzed.

No abstract available.

In this paper, we propose a system-level power exploration methodology for embedded VLIW architectures based on an instruction-level analysis. The instruction-level energy model targets a general pipeline scalar processor; several architectural parameters such as number and type of pipeline stages as well as average stall/latency cycles per instruction and inter-instruction effects are taken into account. The application of the proposed model to VLIW processors results intractable from the point of view of both spatial and temporal complexity (which grow exponentially w.r.t. the number of possible operations in the ISA). To reduce this complexity, the basic model has been extended by assuming that the energy associated with a long instruction is given by the sum of the energy associated with the single operations of the long instruction and the single pipeline stages. The instruction-level energy model has been applied to a simplified VLIW architecture to demonstrate the validity of the proposed approach.

A high-level synthesis approach is proposed for the design of semi-concurrently self-checking devices; attention is focused on data path design. After identifying the reference architecture against which cost and performances should be evaluated, a simultaneous scheduling-and-allocation algorithm is presented, allowing resource sharing between nominal and checking data paths. The algorithm grants that the required checking periodicity is satisfied while minimizing additional costs in terms of functional units. Risk of error aliasing due to resource sharing is analysed.

No abstract available.

Testability analysis and test pattern generation for neural architectures can be performed at a very high abstraction level on the computational paradigm. In this paper, we consider the case of Hopfield's networks, as the simplest example of networks with feedback loops. A behavioral error model based on finite-state machines (FSM's) is introduced. Conditions for controllability, observability and global testability are derived to verify errors excitation and propagation to outputs. The proposed behavioral test pattern generator creates the minimum length test sequence for any digital implementation.

Control-dominated architectures are efficiently described by means of graphical representations based on statecharts. Statecharts descriptions can be automatically translated into HDL representations (VHDL or Verilog) which are directly synthesized into gate-level netlists. This paper describes a set of rules which transform, if possible, a statecharts description into a simpler representation based on hierarchically interconnected FSMs (HFSM). The comparison of the HFSM description with the gate-level synthesized net-list allows to efficiently perform redundancies removal and test pattern generation. Thus, by applying the proposed testing strategy, fully testable implementations can be obtained even for such devices which cannot be satisfactorily analyzed at the gate level only.

Fault-tolerance in embedded systems is a requirement of increasing importance; solutions must achieve a balance between performances and costs that was not usually requested in design of more classical fault-tolerant applications and that involves as a consequence new approaches. A design technique is here proposed supporting fault-tolerance of hardware modules in complex hardware-software systems, fault-tolerance requirements for each hardware-mapped process are specified in terms of time constraints and of relative priorities, and a high-level synthesis methodology allowing to design - for each process - a processor capable of supporting both the nominal execution of the process itself in a fault-free environment and simultaneous execution of a reconfigured pair of processes in a fault-affected environment is defined Performances of the scheduling algorithm, allowing to achieve reconfiguration with minimum resource increase and within the required limits of speed degradation, are evaluated on some relevant instances of algorithms discussed in current literature on high-level synthesis.

A behavioral approach to the impact of errors due to faults in neural computation is analyzed. Starting from a geometrical description of errors affecting neural values, we derive the probability of error detection at the neuron's output and at the network's outputs.>

The problem of mapping neural nets onto massively parallel architectures is considered. The solution examined, based upon regular array structures, can support the mapping of any neural graph. In particular, the case of feed-forward multilayered nets is analyzed, and is proven that in this case the mapping suggested is easily implemented and optimizes a number of relevant figures of merit. The structure of nodes, I/O ports, and switches is taken into account with reference to the neural net case. It is seen that the claims of inherent fault tolerance for neural nets are not actually kept for all classes of faults of a digital implementation; moreover, it is considered that end-of-production defects require restructuring to grant nominal initial operation. An efficient and straightforward solution to the defect-tolerance problem is presented, allowing the most limited redundancy versus good harvesting characteristics.>

In VLSI arrays, redundant cells are added as spares. The proposed approach is applicable as an offline technique at either production time and/or run time. Reconfiguration is implemented by index mapping using a sequence of two operators. A reconfiguration algorithm which utilizes index mapping is proposed. This algorithm uses a new approach to the assignment problem. It is shown that reconfiguration of fault-free cells is equivalent to a covering of faulty cells by spare cells. It is also established that in a two-dimensional array the optimal spare assignment is given by a maximum matching. This translates to a maximum flow. It is shown that a variation of the matching preserves the optimality of the assignment, while reducing the time complexity of the reconfiguration algorithm Characterization theorems for index mapping and simulation results to substantiate the practicality of the approach are presented.>

The paper presents the problem of fault tolerance in VLSI array structures: its aim is to discuss architectures capable of surviving a number of random faults while keeping costs (in terms of added silicon area and of increased processing time) as low as possible. Two different approaches are presented, both based upon introduction of simple patterns of faults and by global reconfiguration techniques (rather than one-to-one substitution of faulty elements by spare ones). Various solutions are compared, and relative performances are discussed in order to determine criteria for selecting the one most suitable to particular applications.

It is considered interesting to identify, from the structure of control flow and of relationships among variables in a program, some properties allowing to point out possible sources of errors or of faulty behavior. In particular, it is found that information about termination of loops and about meaningfulness of acceptance tests in recopery block strategy can be extracted from such structural analysis. Criteria for applying this analysis to programs with arbitrary structures are presented.