Salvatore Pontarelli

Design of a fault tolerant solid state mass memory

This paper describes a novel architecture of fault tolerant solid state mass memory (SSMM) for satellite applications. Mass memories with low-latency time, high throughput, and storage capabilities cannot be easily implemented using space qualified components, due to the inevitable technological delay of these kind of components. For this reason, the choice of commercial off the shelf (COTS) components is mandatory for this application. Therefore, the design of an electronic system for space applications, based on commercial components, must match the reliability requirements using system level methodologies. In the proposed architecture, error-correcting codes are used to strengthen the commercial dynamic random access memory (DRAM) chips, while the system controller is developed by applying fault tolerant design solutions. The main features of the SSMM are the dynamic reconfiguration capability, and the high performances which can be gracefully reduced in case of permanent faults, maintaining part of the system functionality. The paper shows the system design methodology, the architecture, and the simulation results of the SSMM. The properties of the building blocks are described in detail both in their functionality and fault tolerant capabilities. A detailed analysis of the system reliability and data integrity is reported. The graceful degradation capability of our system allows different levels of acceptable performances, in terms of active I/O link interfaces and storage capability. The results also show that the overall reliability of the SSMM is almost the same using different RS coding schemes, allowing a dynamic reconfiguration of the coding to reduce the latency (shorter codewords), or to improve the data integrity (longer codewords). The use of a scrubbing technique can be useful if a high SEU rate is expected, or if the data must be stored for a long period in the SSMM. The reported simulations show the behavior of the SSMM in presence of permanent and transient faults. In fact, we show that the SCU is able to recover from transient faults. On the other hand, using a spare microcontroller also hard faults can be tolerated. The distributed file system confines the unrecoverable fault effects only in a single I/O Interface. In this way, the SSMM maintains its capability to store and read data. The proposed system allows obtaining SSMM characterized by high reliability and high speed due the intrinsic parallelism of the switching matrix.

QCA Circuits for Robust Coplanar Crossing

In this paper, different circuits of Quantum-dot Cellular Automata (QCA) are proposed for the so-called coplanar crossing. Coplanar crossing is one of the most interesting features of QCA because it allows for mono-layered interconnected circuits, whereas CMOS technology needs different levels of metalization. However, the characteristics of the coplanar crossing make it prone to malfunction due to thermal noise or defects. The proposed circuits exploit the majority voting properties of QCA to allow a robust crossing of wires on the Cartesian plane. This is accomplished using enlarged lines and voting. A Bayesian Network (BN) based simulator is utilized for evaluation; results are provided to assess robustness in the presence of cell defects and thermal effects. The BN simulator provides fast and reliable computation of the signal polarization versus normalized temperature. Simulation of the wire crossing circuits at different operating temperatures is provided with respect to defects and a quantitative metric for performance under temperature variations is proposed and assessed.

Fault tolerant solid state mass memory for space applications

In this paper, an innovative fault tolerant solid state mass memory (FTSSMM) architecture is described. Solid state mass memories (SSMMs) are particularly suitable for space applications and more in general for harsh environments such us, for example, nuclear accelerators or avionics. The presented FTSSMM design has been entirely based on commercial off the shelf (COTS) components. In fact, cost competitive and very high performance SSMMs cannot be easily implemented by using space qualified components, due the technological gap and very high cost characterizing these components. In order to match the severe reliability requirements of space applications a COTS-based apparatus must be designed by using suitable system level methodologies (Kluth, 1996 and Fichna, 1998). In the proposed architecture, error-correcting codes are used to strengthen the commercial dynamic random access memory (DRAM) chips, while the system controller has been designed by applying suitable fault tolerant design techniques. Different from other proposed solutions, our architecture fully exploits the reconfiguration capabilities of Reed-Solomon (RS) codes, discriminates between permanent and transient faults reducing the use of spare elements, and provides dynamic reconfiguration and graceful degradation capability, i.e., the FTSSMM performances are gracefully reduced in case of permanent faults, maintaining part of the system functionality. The paper shows the FTSSMM design methodology, the architecture, the reliability analysis, some simulation results, and a description of its implementation based on fast prototyping techniques.

Totally Fault Tolerant RNS Based FIR Filters

In this paper, the design of a finite impulse response (FIR) filter with fault tolerant capabilities based on the residue number system is analyzed. Differently from other approaches that use RNS, the filter implementation is fault tolerant not only with respect to a fault inside the RNS moduli, but also in the reverse converter. An architecture allowing fault masking in the overall RNS FIR filter is presented. It avoids the use of a trivial triple modular redundancy (TMR) to protect the blocks that performs the final stages of the RNS based FIR computation.

Design of a QCA memory with parallel read/serial write

This paper presents a novel memory architecture for implementation by quantum-dot cellular automata (QCA). The proposed architecture combines the advantages of reduced area of a serial memory with the reduced latency in the read operation of a parallel memory. An extensive evaluation with respect to latency and area is pursued. For area analysis, a novel characterization which considers cells in the logic circuitry, interconnect as well as the unused portion of the Cartesian place as QCA layout, is proposed.

Concurrent Error Detection in Reed–Solomon Encoders and Decoders

Reed-Solomon (RS) codes are widely used to identify and correct errors in transmission and storage systems. When RS codes are used for high reliable systems, the designer should also take into account the occurrence of faults in the encoder and decoder subsystems. In this paper, self-checking RS encoder and decoder architectures are presented. The RS encoder architecture exploits some properties of the arithmetic operations in GF(2m). These properties are related to the parity of the binary representation of the elements of the Galois field. In the RS decoder, the implicit redundancy of the received codeword, under suitable assumptions explained in this paper, allows implementing concurrent error detection schemes useful for a wide range of different decoding algorithms with no intervention on the decoder architecture. Moreover, performances in terms of area and delay overhead for the proposed circuits are presented.

Partially Reversible Pipelined QCA Circuits: Combining Low Power With High Throughput

This paper introduces an architecture for quantum-dot cellular automata circuits with the potential for high throughput and low power dissipation. The combination of regions with Bennett clocking and memory storage combines the low power advantage of reversible computing with the high throughput advantage of pipelining. Two case studies are initially presented to evaluate the proposed pipelined architecture in terms of throughput and power consumption due to information dissipation. A general model for assessing power consumption is also proposed. This paper shows that the advantages possible by using a Bennett clocking scheme also depend on circuit topology, thus also confirming the validity of the proposed analysis and model.

Traffic-Aware Design of a High-Speed FPGA Network Intrusion Detection System

Security of todays networks heavily rely on network intrusion detection systems (NIDSs). The ability to promptly update the supported rule sets and detect new emerging attacks makes field-programmable gate arrays (FPGAs) a very appealing technology. An important issue is how to scale FPGA-based NIDS implementations to ever faster network links. Whereas a trivial approach is to balance traffic over multiple, but functionally equivalent, hardware blocks, each implementing the whole rule set (several thousands rules), the obvious cons is the linear increase in the resource occupation. In this work, we promote a different, traffic-aware, modular approach in the design of FPGA-based NIDS. Instead of purely splitting traffic across equivalent modules, we classify and group homogeneous traffic, and dispatch it to differently capable hardware blocks, each supporting a (smaller) rule set tailored to the specific traffic category. We implement and validate our approach using the rule set of the well-known Snort NIDS, and we experimentally investigate the emerging trade-offs and advantages, showing resource savings up to 80 percent based on real-world traffic statistics gathered from an operators backbone.

Novel designs for thermally robust coplanar crossing in QCA

In this paper, different circuit arrangements of quantum-dot cellular automata (QCA) are proposed for the so-called coplanar crossing. These arrangements exploit the majority voting properties of QCA to allow a robust crossing of wires on the Cartesian plane. This is accomplished using enlarged lines and voting. Using a Bayesian network (BN) based simulator, new results are provided to evaluate the robustness to so-called kink of these arrangements to thermal variations. The BN simulator provides fast and reliable computation of the signal polarization versus normalized temperature. It is shown that by modifying the layout, a higher polarization level can be achieved in the routed signal by utilizing the proposed QCA arrangements

A Method to Construct Low Delay Single Error Correction Codes for Protecting Data Bits Only

Error correction codes (ECCs) have been used for decades to protect memories from soft errors. Single error correction (SEC) codes that can correct 1-bit error per word are a common option for memory protection. In some cases, SEC codes are extended to also provide double error detection and are known as SEC-DED codes. As technology scales, soft errors on registers also became a concern and, therefore, SEC codes are used to protect registers. The use of an ECC impacts the circuit design in terms of both delay and area. Traditional SEC or SEC-DED codes developed for memories have focused on minimizing the number of redundant bits added by the code. This is important in a memory as those bits are added to each word in the memory. However, for registers used in circuits, minimizing the delay or area introduced by the ECC can be more important. In this paper, a method to construct low delay SEC or SEC-DED codes that correct errors only on the data bits is proposed. The method is evaluated for several data block sizes, showing that the new codes offer significant delay reductions when compared with traditional SEC or SEC-DED codes. The results for the area of the encoder and decoder also show substantial savings compared to existing codes.