Marco Re

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.

Residue Number System for Low-Power DSP Applications

In previous works (Cardarilli et al., 2000) we performed different experiments implementing FIR filtering structures. Each filter was implemented using both the twos complement system (TCS) and the residue number system (RNS) number representations. The comparison of these two implementations allows to conclude that, for these applications, the RNS uses less power than the TCS counterpart. The aim of the present paper is to highlight the reasons of this power consumption reduction.

Low-power adaptive filter based on RNS components

In this paper a low-power implementation of an adaptive FIR filter is presented. The filter is designed to meet the constraints of channel equalization for fixed wireless communications that typically requires a large number of taps, but a serial updating of the filter coefficients, based on the least mean squares (LMS) algorithm, is allowed. Previous work showed that the use of the residue number system (RNS) for the variable FIR filter grants advantages both in area and power consumption. On the other hand, the use of a binary serial implementation of the adaptation algorithm eliminates the need for complex scaling circuits in RNS. The advantages in terms of area and speed of the presented filter, with respect to its twos complement counterpart, are evaluated for implementations in standard cells.

Reducing power dissipation in FIR filters using the residue number system

The aim of this work is to reduce the power dissipated in high order finite impulse response (FIR) filters, while maintaining the delay unchanged. We compare in terms of performance, area, and power dissipation the implementation of a traditional FIR filter with a residue number system (RNS) based one. The resulting implementations, designed to work at the same clock rate, show that the RNS filter is smaller and consumes less power than the traditional one for a number of taps larger than eight.

Tradeoffs between residue number system and traditional FIR filters

In this work, a study on the implementation of FIR filters in the Residue Number System (RNS) is carried out. For different configurations, RNS filters are compared with filters realized in the traditional twos complement system (TCS) in terms of delay, area and power dissipation. The resulting implementations show that the RNS filters are smaller and consume less power than the corresponding ones in TCS, when the number of taps is larger than sixteen.

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.

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.

Low-power implementation of polyphase filters in Quadratic Residue Number system

The aim of this work is the reduction of the power dissipated in digital filters, while maintaining the timing unchanged. A polyphase filter bank in the Quadratic Residue Number System (QRNS) has been implemented and then compared, in terms of performance, area, and power dissipation to the implementation of a polyphase filter bank in the traditional twos complement system (TCS). The resulting implementations, designed to have the same clock rates, show that the QRNS filter is smaller and consumes less power than the TCS one.

Implementation of digital filters in carry-save residue number system

In this work, we present the implementation of a finite impulse response (FIR) filter in the residue number system (RNS), in which we use a carry-save scheme in the binary representation of the residues to speed-up modular additions. We compare the carry-save RNS implementation with the implementations of the same filter in the traditional binary system and in plain RNS. Results show that the carry-save RNS filter is much faster and its energy dissipation per cycle comparable. Furthermore, we show that a multiple supply voltage approach for the plain RNS filter can lead to an additional reduction in power dissipation without performance degradation.