Hardware Reference
In-Depth Information
create
SLEEP
WAIT
sleep
activate
signal
wait
dispatching
terminate
READY
RUN
ZOMBIE
preemption
end_cycle
FREE
resume
IDLE
TIMER
Figure 10.7
State transition diagram in DICK.
10.3
DATA STRUCTURES
In any operating system, the information about a task are stored in a data structure, the
Task Control Block
(TCB). In particular, a TCB contains all the parameters specified
by the programmer at creation time, plus other temporary information necessary to the
kernel for managing the task. In a real-time system, the typical fields of a TCB are
shown in Figure 10.8 and contain the following information:
An identifier; that is, a character string used by the system to refer the task in
messages to the user;
The memory address corresponding to the first instruction of the task;
The task type (periodic, aperiodic, or sporadic);
The task criticality (hard, soft, or non-real-time);
The priority (or value), which represents the importance of the task with respect
to the other tasks of the application;
The current state (ready, running, idle, waiting, and so on);
The worst-case execution time;
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