Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Chapter 20
STATE SPACE COMPRESSION IN HISTORY
DRIVEN QUASI-STATIC SCHEDULING
Antonio G. Lomeña 1 , Marisa López-Vallejo 1 , Yosinori Watanabe 2 and
Alex Kondratyev 2
1 Electronic Engineering Department. ETSI Telecomunicación, Universidad Politécnica de
Madrid, Ciudad Universitaria s/n, 28040, Madrid, Spain, E-mail:
{lomena,marisa}@die.upm.es; 2 Cadence Berkeley Laboratories, 2001 Addison Street, 3rd
Floor, Berkeley, CA 94704, USA, E-mail: {watanabe,kalex}@cadence.com
Abstract. This paper presents efficient compression techniques to avoid the state space
explosion problem during quasi-static task scheduling of embedded, reactive systems.
Our application domain is targeted to one-processor software synthesis, and the scheduling
process is based on Petri net reachability analysis to ensure cyclic, bounded and live programs.
We suggest two complementary compression techniques that effectively reduce the size of the
generated schedule and make the problem tractable for large specifications.
Our experimental results reveal a significant reduction in algorithmic complexity (both in
memory storage and CPU time) obtained for medium and large size problems.
Key words: hash table, state explosion, quasi-static scheduling
1. INTRODUCTION
During the last years, the use of design methodologies based on formal
methods has been encouraged as a means to tackle the increasing complexity
in the design of electronic systems. However, traditional formal verification
methods such as model checking or reachability analysis have the drawback
of requiring huge computing resources.
In this paper we address the problem of software synthesis for embedded,
reactive systems, using Petri nets (PNs) as our underlying formal model and
reachability analysis as a way to formally obtain a valid quasi-static task
schedule that ensures cyclic, buffer bounded, live programs [2]. To overcome
the state space explosion problem that is inherent to the reachability analysis,
we suggest two complementary techniques for schedule compression. The first
technique explores the reachability space at a coarser granularity level by
doing scheduling in big moves that combine the firing of several transitions
at once. The second technique uses a dynamic, history based criterion that
prunes the state space of uninteresting states for our application domain.
The paper is organized as follows. Next section reviews previous work
related to the reduction of the state space explosion. Section 3 states the
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A Jerraya et al. (eds.), Embedded Software for SOC, 261–274, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.