DESIGN PROCESS OF REAL-TIME OPERATING SYSTEMS (RTOS) - Software Design for Six-Sigma: A Roadmap for Excellence - page 67

TABLE 3.3 Task Management Design Options and Comparison

Purpose Advantages Disadvantages Efficiency Implementation

Ta s k S t a t e s Organizes tasks for the

operating system

The operating system
is aware of the state
of each task so they
can be scheduled
appropriately

Requires additional
complexity on the
operating system

Improves efficiency
because the
operating system
only schedules tasks
that are ready to run

Adds complexity in the
operating system
because it must assign,
read, and keep track of
task states

Reentrancy Allows tasks to be

reexecuted
concurrently

Allows reuse of
existing code

Each instance of the
task or process
requires its own data
structure and
run-time stack

The code is more
efficient, because it
can be used multiple
times

Adds complexity to the
operating system and
application

Context Switching Provides a method of

saving of data from
the current task so a
new task can be
executed

Allows for preemption
in a multitasking
environment

Takes time to switch
between tasks

Can improve overall
efficiency by
allowing higher
priority tasks to run
first, but takes time
to switch in and out
of task-specific data

Is complex to implement
in operating system; the
operating system must
support multitasking,
preemption, and
provide a method to
save and retrieve data

TCB (Task
Control Block)

Saves data specific to
task, such as
registers and
program counter

Keeps all data specific
to a tasks together in
a structure

A predetermined size
of memory must be
set aside for each
task

Can improve efficiency
because all task data
are kept together

The operating system
must include data
structures for tasks