Studio di un'infrastruttura di supporto al controllo e alla gestione della circolazione dei treni nelle stazioni

Il sistema ferroviario ha sempre ricoperto un ruolo rilevante nel nostro Paese sia per il trasporto di persone, sia per il trasporto di merci: risulta, quindi, essenziale per il commercio e per il turismo. A differenza della strada in cui i veicoli circolano “a vista”, una ferrovia richiede che i sistemi di distanziamento dei treni siano indipendenti dalla visibilità dei veicoli, poiché gli spazi di frenatura sono solitamente molto maggiori della distanza di visibilità stessa. Per questo motivo i sistemi di segnalamento e sicurezza ricoprono un ruolo di primo piano. Nel tempo sono stati effettuati ingenti investimenti che hanno portato all'impiego di nuove tecnologie le quali hanno permesso la progettazione di sistemi safety critical contenenti componenti informatici hardware e software. La caratteristica principale di tali sistemi è la proprietà di non arrecare danno alla vita umana o all'ambiente: tale proprietà viene comunemente associata al termine anglosassone safety per distinguerla dall’accezione di "protezione da violazioni all'integrità del sistema" che il termine "sicurezza" usualmente assume. Lo sviluppo economico e tecnologico a cui abbiamo assistito nell’ultimo ventennio ha inevitabilmente reso tali sistemi ancora più sofisticati e di conseguenza complessi, richiedendo allo stesso tempo requisiti e garanzie di buon funzionamento sempre più marcati ed articolati. È proprio a questi motivi che si devono gli studi su quella che viene definita la dependability dei sistemi di computazione, verso cui si concentrano e convogliano buona parte degli sforzi e delle risorse in fase di ricerca e progettazione. Il lavoro di tesi che segue è stato svolto in collaborazione con due grandi imprese del territorio nazionale: RFI (Reti Ferroviarie Italiane) e Sirti. Inizialmente abbiamo interagito con RFI per entrare nell’ambiente ferroviario ed assimilarne il lessico e i bisogni. All’interno di RFI è stato effettuato un tirocinio nel quale ci siamo occupati del “processo off-line” riguardante la gestione in sicurezza di una stazione; tale attività deve essere effettuata da RFI prima della messa in esercizio di una nuova stazione. Per far questo abbiamo dovuto utilizzare i programmi di preparazione dei dati messi a disposizione da Sirti. In un secondo momento abbiamo approfondito l’argomentazione della safety interfacciandoci con Sirti, una delle società che forniscono sistemi safety critical computerizzati per il controllo delle stazioni. In collaborazione con essa ci siamo addentrati nel loro sistema scoprendo le loro scelte implementative e come hanno raggiunto i loro obiettivi di safety. Infine, ci siamo occupati dell'inserimento nel sistema di una nuova funzionalità, per aumentarne l’affidabilità e la sicurezza, e delle problematiche relative all'impiego del componente che la realizza.

False Error Study of On-line Soft Error Detection Mechanisms

With technology scaling, vulnerability to soft errors in random logic is increasing. There is a need for on-line error detection and protection for logic gates even at sea level. The error checker is the key element for an on-line detection mechanism. We compare three different checkers for error detection from the point of view of area, power and false error detection rates. We find that the double sampling checker (used in Razor), is the simplest and most area and power efficient, but suffers from very high false detection rates of 1.15 times the actual error rates. We also find that the alternate approaches of triple sampling and integrate and sample method (I&S) can be designed to have zero false detection rates, but at an increased area, power and implementation complexity. The triple sampling method has about 1.74 times the area and twice the power as compared to the Double Sampling method and also needs a complex clock generation scheme. The I&S method needs about 16% more power with 0.58 times the area as double sampling, but comes with more stringent implementation constraints as it requires detection of small voltage swings.

Modified Stability Checking for On-Line Error Detection

The paper propose a unified error detection technique, based on stability checking, for on-line detection of delay, crosstalk and transient faults in combinational circuits and SEUs in sequential elements. The proposed method, called modified stability checking (MSC), overcomes the limitations of the earlier stability checking methods. The paper also proposed a novel checker circuit to realize this scheme. The checker is self-checking for a wide set of realistic internal faults including transient faults. Extensive circuit simulations have been done to characterize the checker circuit. A prototype checker circuit for a 1mm2 standard cell array has been implemented in a 0.13mum process.

Error Detection and Recovery for Robot Motion Planning with Uncertainty

Robots must plan and execute tasks in the presence of uncertainty. Uncertainty arises from sensing errors, control errors, and uncertainty in the geometry of the environment. The last, which is called model error, has received little previous attention. We present a framework for computing motion strategies that are guaranteed to succeed in the presence of all three kinds of uncertainty. The motion strategies comprise sensor-based gross motions, compliant motions, and simple pushing motions.

Real-time error detection but not error correction drives automatic visuomotor adaptation

We investigated the role of visual feedback of task performance in visuomotor adaptation. Participants produced novel two degrees of freedom movements (elbow flexion-extension, forearm pronation-supination) to move a cursor towards visual targets. Following trials with no rotation, participants were exposed to a 60A degrees visuomotor rotation, before returning to the non-rotated condition. A colour cue on each trial permitted identification of the rotated/non-rotated contexts. Participants could not see their arm but received continuous and concurrent visual feedback (CF) of a cursor representing limb position or post-trial visual feedback (PF) representing the movement trajectory. Separate groups of participants who received CF were instructed that online modifications of their movements either were, or were not, permissible as a means of improving performance. Feedforward-mediated performance improvements occurred for both CF and PF groups in the rotated environment. Furthermore, for CF participants this adaptation occurred regardless of whether feedback modifications of motor commands were permissible. Upon re-exposure to the non-rotated environment participants in the CF, but not PF, groups exhibited post-training aftereffects, manifested as greater angular deviations from a straight initial trajectory, with respect to the pre-rotation trials. Accordingly, the nature of the performance improvements that occurred was dependent upon the timing of the visual feedback of task performance. Continuous visual feedback of task performance during task execution appears critical in realising automatic visuomotor adaptation through a recalibration of the visuomotor mapping that transforms visual inputs into appropriate motor commands.

Developmental and individual differences in novelty and error detection in 10-year-old children and young adults /

Event-related potentials were recorded from 10-year-old children and young adults in order to examine the developmental dififerences in two frontal lobe functions: detection of novel stimuli during an auditory novelty oddball task, and error detection during a visual flanker task. All participants showed a parietally-maximal P3 in response to auditory stimuli. In children, novel stimuli generated higher P3 amplitudes at the frontal site compared with target stimuli, whereas target stimuli generated higher P3 amplitudes at the parietal site compared with novel stimuli. Adults, however, had higher P3 amplitude to novel tones compared with target tones at each site. Children also had greater P3 amplitude at more parietal sites than adults during the novelty oddball and flanker tasks. Furthermore, children and adults did not show a significant reduction in P3 amplitude from the first to second novel stimulus presentation. No age differences were found with respect to P3 latency to novel and target stimuli. These findings suggest that the detection of novel and target stimuli is mature in 10-year-olds. Error trials typically elicit a negative ERP deflection (the ERN) with a frontal-central scalp distribution that may reflect response monitoring. There is also evidence of a positive ERP peak (the Pe) with a posterior scalp distribution which may reflect subjective recognition of a response. Both children and adults showed an ERN and Pe maximal at frontal-central sites. Children committed more errors, had smaller ERN across sites, and had a larger Pe at the parietal site than adults. This suggests that response monitoring is still immature in 10-year-olds whereas recognition of and emotional responses to errors may be similar in children and adults.

The effects of manipulated augmented sensory feedback on error detection when using a touch screen

The purpose of the present study was to determine which augmented sensory modality would best develop subjective error-detection capabilities of learners performing a spatial-temporal task when using a touch screen monitor. Participants were required to learn a 5-digit key-pressing task in a goal time of 2550 ms over 100 acquisition trials on a touch screen. Participants were randomized into 1 of 4 groups: 1) visual-feedback (colour change of button when selected), 2) auditory-feedback (click sound when button was selected), 3) visual-auditory feedback (both colour change and click sound when button was selected), and 4) no-feedback (no colour change or click sound when button was selected). Following each trial, participants were required to provide a subjective estimate regarding their performance time in relation to the actual time it took for them complete the 5-digit sequence. A no-KR retention test was conducted approximately 24-hours after the last completed acquisition trial. Results showed that practicing a timing task on a touch screen augmented with both visual and auditory information may have differentially impacted motor skill acquisition such that removal of one or both sources of augmented feedback did not result in a severe detriment to timing performance or error detection capabilities of the learner. The present study reflects the importance of multimodal augmented feedback conditions to maximize cognitive abilities for developing a stronger motor memory for subjective error-detection and correction capabilities.

S-SETA: Selective Software-Only Error-Detection Technique Using Assertions

Software-based techniques offer several advantages to increase the reliability of processor-based systems at very low cost, but they cause performance degradation and an increase of the code size. To meet constraints in performance and memory, we propose SETA, a new control-flow software-only technique that uses assertions to detect errors affecting the program flow. SETA is an independent technique, but it was conceived to work together with previously proposed data-flow techniques that aim at reducing performance and memory overheads. Thus, SETA is combined with such data-flow techniques and submitted to a fault injection campaign. Simulation and neutron induced SEE tests show high fault coverage at performance and memory overheads inferior to the state-of-the-art.

Error detection and correction in binary parallel digital computers /

"Retyped October, 1964"