190 research outputs found
Engineering change in a non-deterministic FSM setting
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Decomposition of sequential and concurrent models
Le macchine a stati finiti (FSM), sistemi di transizioni (TS) e le reti di Petri (PN) sono importanti modelli formali per la progettazione di sistemi. Un problema fodamentale è la conversione da un modello all'altro. Questa tesi esplora il mondo delle reti di Petri e della decomposizione di sistemi di transizioni. Per quanto riguarda la decomposizione dei sistemi di transizioni, la teoria delle regioni rappresenta la colonna portante dell'intero processo di decomposizione, mirato soprattutto a decomposizioni che utilizzano due sottoclassi delle reti di Petri: macchine a stati e reti di Petri a scelta libera. Nella tesi si dimostra che una proprietà chiamata ``chiusura rispetto all'eccitazione" (excitation-closure) è sufficiente per produrre un insieme di reti di Petri la cui sincronizzazione è bisimile al sistema di transizioni (o rete di Petri di partenza, se la decomposizione parte da una rete di Petri), dimostrando costruttivamente l'esistenza di una bisimulazione. Inoltre, è stato implementato un software che esegue la decomposizione dei sistemi di transizioni, per rafforzare i risultati teorici con dati sperimentali sistematici. Nella seconda parte della dissertazione si analizza un nuovo modello chiamato MSFSM, che rappresenta un insieme di FSM sincronizzate da due primitive specifiche (Wait State - Stato d'Attesa e Transition Barrier - Barriera di Transizione). Tale modello trova un utilizzo significativo nella sintesi di circuiti sincroni a partire da reti di Petri a scelta libera. In particolare vengono identificati degli errori nell'approccio originale, fornendo delle correzioni.Finite State Machines (FSMs), transition systems (TSs) and Petri nets (PNs) are important models of computation ubiquitous in formal methods for modeling systems. Important problems involve the transition from one model to another. This thesis explores Petri nets, transition systems and Finite State Machines decomposition and optimization. The first part addresses decomposition of transition systems and Petri nets, based on the theory of regions, representing them by means of restricted PNs, e.g., State Machines (SMs) and Free-choice Petri nets (FCPNs). We show that the property called ``excitation-closure" is sufficient to produce a set of synchronized Petri nets bisimilar to the original transition system or to the initial Petri net (if the decomposition starts from a PN), proving by construction the existence of a bisimulation. Furthermore, we implemented a software performing the decomposition of transition systems, and reported extensive experiments. The second part of the dissertation discusses Multiple Synchronized Finite State Machines (MSFSMs) specifying a set of FSMs synchronized by specific primitives: Wait State and Transition Barrier. It introduces a method for converting Petri nets into synchronous circuits using MSFSM, identifies errors in the initial approach, and provides corrections
Retiming and Resynthesis with Sweep Are Complete for Sequential Transformation
Abstract-There is a long history of investigations and debates on whether a sequence of retiming and resynthesis is complete for all sequential transformations (on steady states). It has been shown that the sweep operation, which adds or removes registers not used by any output, is necessary for some sequential transformations. However, it is an open question whether retiming and resynthesis with sweep are complete. This paper proves that the operations are complete, but with one caveat: at least one resynthesis operation needs to look through the register boundary into the logic of previous cycle. We showed that this one-cycle reachability is required for retiming and resynthesis to be complete for re-encodings with different code length. This requirement comes from the fact that Boolean circuit is used for a discrete function thus its range needs to be computed by a traversal of the circuit. In theory, five operations in the order of sweep, resynthesis, retiming, resynthesis, and sweep are already complete. However, some practical limitations on resynthesis must be considered. The complexity of retiming and resynthesis verification is also discussed
Test Generation Based on CLP
Functional ATPGs based on simulation are fast,
but generally, they are unable to cover corner cases, and
they cannot prove untestability. On the contrary, functional
ATPGs exploiting formal methods, being exhaustive,
cover corner cases, but they tend to suffer of the state
explosion problem when adopted for verifying large designs.
In this context, we have defined a functional ATPG
that relies on the joint use of pseudo-deterministic simulation
and Constraint Logic Programming (CLP), to
generate high-quality test sequences for solving complex
problems. Thus, the advantages of both simulation-based
and static-based verification techniques are preserved, while
their respective drawbacks are limited. In particular, CLP,
a form of constraint programming in which logic programming
is extended to include concepts from constraint satisfaction,
is well-suited to be jointly used with simulation. In
fact, information learned during design exploration by simulation
can be effectively exploited for guiding the search of
a CLP solver towards DUV areas not covered yet. The test
generation procedure relies on constraint logic programming
(CLP) techniques in different phases of the test generation
procedure.
The ATPG framework is composed of three functional
ATPG engines working on three different models of the
same DUV: the hardware description language (HDL)
model of the DUV, a set of concurrent EFSMs extracted
from the HDL description, and a set of logic constraints
modeling the EFSMs. The EFSM paradigm has been selected
since it allows a compact representation of the DUV
state space that limits the state explosion problem typical
of more traditional FSMs. The first engine is randombased,
the second is transition-oriented, while the last is
fault-oriented.
The test generation is guided by means of transition coverage and fault coverage. In particular, 100% transition
coverage is desired as a necessary condition for fault
detection, while the bit coverage functional fault model
is used to evaluate the effectiveness of the generated test
patterns by measuring the related fault coverage.
A random engine is first used to explore the DUV state
space by performing a simulation-based random walk. This
allows us to quickly fire easy-to-traverse (ETT) transitions
and, consequently, to quickly cover easy-to-detect (ETD)
faults. However, the majority of hard-to-traverse (HTT)
transitions remain, generally, uncovered.
Thus, a transition-oriented engine is applied to
cover the remaining HTT transitions by exploiting a
learning/backjumping-based strategy.
The ATPG works on a special kind of EFSM, called
SSEFSM, whose transitions present the most uniformly
distributed probability of being activated and can be effectively
integrated to CLP, since it allows the ATPG to invoke
the constraint solver when moving between EFSM states.
A constraint logic programming-based (CLP) strategy is
adopted to deterministically generate test vectors that satisfy
the guard of the EFSM transitions selected to be traversed. Given a transition of the SSEFSM, the solver
is required to generate opportune values for PIs that enable
the SSEFSM to move across such a transition.
Moreover, backjumping, also known as nonchronological
backtracking, is a special kind of backtracking
strategy which rollbacks from an unsuccessful
situation directly to the cause of the failure. Thus,
the transition-oriented engine deterministically backjumps
to the source of failure when a transition, whose guard
depends on previously set registers, cannot be traversed.
Next it modifies the EFSM configuration to satisfy the
condition on registers and successfully comes back to the
target state to activate the transition.
The transition-oriented engine generally allows us to
achieve 100% transition coverage. However, 100% transition
coverage does not guarantee to explore all DUV corner
cases, thus some hard-to-detect (HTD) faults can escape
detection preventing the achievement of 100% fault coverage.
Therefore, the CLP-based fault-oriented engine is finally
applied to focus on the remaining HTD faults.
The CLP solver is used to deterministically search for
sequences that propagate the HTD faults observed, but not
detected, by the random and the transition-oriented engine.
The fault-oriented engine needs a CLP-based representation
of the DUV, and some searching functions to generate
test sequences. The CLP-based representation is automatically
derived from the S2EFSM models according to the
defined rules, which follow the syntax of the ECLiPSe CLP
solver. This is not a trivial task, since modeling the
evolution in time of an EFSM by using logic constraints
is really different with respect to model the same behavior
by means of a traditional HW description language. At
first, the concept of time steps is introduced, required to
model the SSEFSM evolution through the time via CLP.
Then, this study deals with modeling of logical variables
and constraints to represent enabling functions and update
functions of the SSEFSM.
Formal tools that exhaustively search for a solution frequently
run out of resources when the state space to be analyzed
is too large. The same happens for the CLP solver,
when it is asked to find a propagation sequence on large sequential
designs. Therefore we have defined a set of strategies
that allow to prune the search space and to manage the
complexity problem for the solver
Local structure helps learning optimized automata in recurrent neural networks
Deterministic behavior can be modeled conveniently in the framework of finite automata. We present a recurrent neural network model based on biologically plausible circuit motifs that can learn deterministic transition models from given input sequences. Furthermore, we introduce simple structural constraints on the connectivity that are inspired by biology. Simulation results show that this leads to great improvements in terms of training time, and efficient use of resources in the converged system. Previous work has shown how specific instances of finite-state machines (FSMs) can be synthesized in recurrent neural networks by interconnecting multiple soft winner-take-all (SWTA) circuits - small circuits that can faithfully reproduce many computational properties of cortical networks. We extend this framework with a reinforcement learning mechanism to learn correct state transitions as input and reward signals are provided. Not only does the network learn a model for the observed sequences, and encode it in the recurrent synaptic weights, it also finds solutions that are close-to-optimal in the number of states required to model the target system, leading to efficient scaling behavior as the size of the target problems increases
Automatic generation of hardware/software interfaces
Enabling new applications for mobile devices often requires the use of specialized hardware to reduce power consumption. Because of time-to-market pressure, current design methodologies for embedded applications require an early partitioning of the design, allowing the hardware and software to be developed simultaneously, each adhering to a rigid interface contract. This approach is problematic for two reasons: (1) a detailed hardware-software interface is difficult to specify until one is deep into the design process, and (2) it prevents the later migration of functionality across the interface motivated by efficiency concerns or the addition of features. We address this problem using the Bluespec Codesign Language~(BCL) which permits the designer to specify the hardware-software partition in the source code, allowing the compiler to synthesize efficient software and hardware along with transactors for communication between the partitions. The movement of functionality across the hardware-software boundary is accomplished by simply specifying a new partitioning, and since the compiler automatically generates the desired interface specifications, it eliminates yet another error-prone design task. In this paper we present BCL, an extension of a commercially available hardware design language (Bluespec SystemVerilog), a new software compiling scheme, and preliminary results generated using our compiler for various hardware-software decompositions of an Ogg Vorbis audio decoder, and a ray-tracing application.National Science Foundation (U.S.) (NSF (#CCF-0541164))National Research Foundation of Korea (grant from the Korean Government (MEST) (#R33-10095)
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