Lecture Notes in Computer Science 3472

13 Real-Time and Hybrid Systems Testing 363
recX .P1 – process P1 that is recursive, i.e. it may have an infinite
execution. Every free occurrence of X within P1 represents
a recursive call of the expression recX .P1.
X – recursive call of the surrounding recursive process recX .P1.
RTMonitor Example: We will now model the RTMonitor example according
to the constraint graph given in Figure 13.2. An ACSR model of RT Monitor is
shown in Figure 13.3. It does not use any actions as resources are not considered
in this example. The model excessively uses the concept of temporal scopes to
model the allowed time intervals.
RT Monitor = recX .((Start,1).PMA1 )
PMA1
PMA2
PMB1
PMB2
Pok
Pmiss
Pearly
= ∅ ∞ △ (Pos1,1)
10 (Pearly , PMA2, NIL)
= ∅ ∞ △ (Pos1,1)
20
(PMB1, Pmiss, NIL)
= ∅ ∞ △ (Pos2,1)
20 (Pearly , PMB2, NIL)
= ∅ ∞ △ (Pos2,1)
10
(Pok, Pmiss, NIL)
=(Passed, 1).X
=(TimeOut,1).(Reset, 1).X
=(TooF ast, 1).(Reset, 1).X
Fig. 13.3. ACSR model of the real-time monitor example
First, process RT Monitor is defined as a recursive process where the recursion
is performed in subprocess Pok . RT Monitor is waiting an unlimited
time period for the occurrence of event (Start,1) and continues then with process
PMA1. Process PMA1 together with process PMA2 checks whether event
(Pos1, 1) occurs within time interval [10, 30) and continues then with process
PMB1. If the event comes too early respectively too late, the corresponding output
events (T ooF ast, 1) or (TimeOut,1) are generated by process Pearly respectively
Pmiss. After receiving an input event (Reset, 1) process RT Monitor
is recursively called. Analogous to PMA1 andPMA2, processes PMB1 and PMB2
check whether event (Pos2, 1) occurs within time interval [20, 30). After that,
control is taken over by process Pok that emits the output event (P assed, 1) and
then recursively calls RT Monitor.
The use of a process algebra like ACSR allows to abstract from the real
application behavior by modeling only the dynamic aspects of interaction. In
case of ACSR these aspects of interaction include events as well as resource
consuming actions. Mechanisms like temporal scope and time consuming actions
can express the temporal behavior of the application. ACSR does not support
the modeling of numerical calculations or direct communication of parameters.
Therefore, the use of ACSR is adequate in cases where the behavior of event
communication and resource consuming actions of concurrent processes are the
only interesting aspects.