The TASM Language Reference Manual Version 1.1 - Synrc

Chapter 1
Introduction
This document serves as the central reference for the syntax and semantics of the Timed
Abstract State Machine (TASM) language. The TASM language is a specification language
used to specify and simulate the behavior of real-time systems. The type of
behavior that can be expressed in the TASM language includes functional behavior, in
pre-condition/effect style, timing behavior, and resource consumption behavior. The
TASM language is based on the principles of state-transition systems and durative
actions. The TASM language is an extension of the Abstract State Machine (ASM)
language [5], formerly known as evolving algebra. The TASM language has been designed
to specify and simulate the behavior of reactive real-time embedded systems.
Reactive systems are a class of systems that operate in an infinite loop, in a sequence
of ”sense-reason-actuate” actions. In reactive systems, the environment is the master of
the interaction, and the computer system must exhibit correct dynamic behavior during
its continuous interaction with the environment. The real-time facet of target systems
requires that operational correctness is not limited to functional correctness but must
also include timing correctness. Timing correctness reflects the physical reality that
actions take a finite amount of time to complete and hence a system will take a finite
amount of time to produce a response to an environment stimulus. The design and development
of real-time systems must ensure that a response to environmental stimulus
happens in a predictable amount of time (or at least be bounded). The embedded facet
of target systems requires that operational correctness is not limited to functional correctness
and timing correctness but must also include resource utilization correctness.
Embedded systems are typically limited in terms of resources (memory, processor, bus
bandwidth, etc.) and being able to predict that resource utilization will fall within certain
bounds is paramount to establishing operational correctness. The TASM language
provides a language that enables the specification and simulation of system behavior
along the function, time, and resource axes. Incorporating these three criteria in an
integrated language is a key contribution of the TASM language. The TASM language
forms the basis of a specification framework for embedded real-time systems. The
types of systems targeted by the specification language are those typically found in
process control in the aerospace industry (e.g., avionics) and the automotive industry
(e.g., drive-by-wire electronics).
5