S. Di Carlo

Control-flow checking via regular expressions

The present paper explains a new approach to program control flow checking. The check has been inserted at source-code level using a signature methodology based on regular expressions. The signature checking is performed without a dedicated watchdog processor but resorting to inter-process communication (IPC) facilities offered by most of the modern operating systems. The proposed approach allows very low memory overhead and trade-off between fault latency and program execution time overhead.

Software-Based Self-Test of Set-Associative Cache Memories

Embedded microprocessor cache memories suffer from limited observability and controllability creating problems during in-system tests. This paper presents a procedure to transform traditional march tests into software-based self-test programs for set-associative cache memories with LRU replacement. Among all the different cache blocks in a microprocessor, testing instruction caches represents a major challenge due to limitations in two areas: 1) test patterns which must be composed of valid instruction opcodes and 2) test result observability: the results can only be observed through the results of executed instructions. For these reasons, the proposed methodology will concentrate on the implementation of test programs for instruction caches. The main contribution of this work lies in the possibility of applying state-of-the-art memory test algorithms to embedded cache memories without introducing any hardware or performance overheads and guaranteeing the detection of typical faults arising in nanometer CMOS technologies.

An effective distributed BIST architecture for RAMs

The present paper proposes a solution to the problem of testing a system containing many distributed memories of different sizes. The proposed solution relies in the development of a BIST architecture characterized by a single BIST processor, implemented as a microprogrammable machine and able to execute different test algorithms, a wrapper for each SRAM including standard memory BIST modules, and an interface block to manage the communications between the SRAM and the BIST processor. Both area overhead and routing costs are minimized, and a scan-based approach allows full diagnostic capabilities of the faults possibly detected in the memories under test.

A programmable BIST architecture for clusters of multiple-port SRAMs

This paper presents a BIST architecture, based on a single microprogrammable BIST processor and a set of memory wrappers, designed to simplify the test of a system containing many distributed multi-port SRAMs of different sizes (number of bits, number of words), access protocol (asynchronous, synchronous), and timing.

Programmable built-in self-testing of embedded RAM clusters in system-on-chip architectures

Multiport memories are widely used as embedded cores in all communication system-on-chip devices. Due to their high complexity and very low accessibility, built-in self-test (BIST) is the most common solution implemented to test the different memories embedded in the system. This article presents a programmable BIST architecture based on a single microprogrammable BIST processor and a set of memory wrappers designed to simplify the test of a system containing a large number of distributed multiport memories of different sizes (number of bits, number of words), access protocols (asynchronous, synchronous), and timing.

March AB, March AB1: new March tests for unlinked dynamic memory faults

Among the different types of algorithms proposed to test static random access memories (SRAMs), March tests have proven to be faster, simpler and regularly structured. New memory production technologies introduce new classes of faults usually referred to as dynamic memory faults. A few March tests for dynamic fault, with different fault coverage, have been published. In this paper, we propose new March tests targeting unlinked dynamic faults with lower complexity than published ones. Comparison results show that the proposed March tests provide the same fault coverage of the known ones, but they reduce the test complexity, and therefore the test time

Statistical Reliability Estimation of Microprocessor-Based Systems

What is the probability that the execution state of a given microprocessor running a given application is correct, in a certain working environment with a given soft-error rate? Trying to answer this question using fault injection can be very expensive and time consuming. This paper proposes the baseline for a new methodology, based on microprocessor error probability profiling, that aims at estimating fault injection results without the need of a typical fault injection setup. The proposed methodology is based on two main ideas: a one-time fault-injection analysis of the microprocessor architecture to characterize the probability of successful execution of each of its instructions in presence of a soft-error, and a static and very fast analysis of the control and data flow of the target software application to compute its probability of success. The presented work goes beyond the dependability evaluation problem; it also has the potential to become the backbone for new tools able to help engineers to choose the best hardware and software architecture to structurally maximize the probability of a correct execution of the target software.

Specification and design of a new memory fault simulator

This paper presents a new fault simulator architecture for RAM memories. The key features of the proposed tool are: (1) user-definable fault models, test algorithm, and memory architecture; (2) very fast simulation algorithm; (3) ability to compute the coverage of any provided test sequence with respect to a user-defined set of fault models, and to eliminate redundant operations; (4) assessment of the power consumption generated by the test application. Moreover, the tool is able to modify the test algorithm in order to guarantee the compliance to user-defined power consumption constraints.

Automatic March tests generation for static and dynamic faults in SRAMs

New memory production modern technologies introduce new classes of faults usually referred to as dynamic memory faults. Although some hand-made March tests to deal with these new faults have been published, the problem of automatically generate March tests for dynamic faults has still to be addressed, in this paper we propose a new approach to automatically generate March tests with minimal length for both static and dynamic faults. The proposed approach resorts to a formal model to represent faulty behaviors in a memory and to simplify the generation of the corresponding tests.

Static analysis of SEU effects on software applications

Control flow errors have been widely addressed in literature as a possible threat to the dependability of computer systems, and many clever techniques have been proposed to detect and tolerate them. Nevertheless, it has never been discussed if the overheads introduced by many of these techniques are justified by a reasonable probability of incurring control flow errors. This paper presents a static executable code analysis methodology able to compute, depending on the target microprocessor platform, the upper-bound probability that a given application incurs in a control flow error.