Hardware Reference
In-Depth Information
RECEIVE
send
receive
WAIT
signal
wait
dispatching
activate
terminate
READY
RUN
ZOMBIE
preemption
end_cycle
delay
FREE
resume
IDLE
TIMER
DELAY
Figure 10.6
State transition diagram including RECEIVE, DELAY, and ZOMBIE states.
and DELAY are not present. However, these services can easily be developed on top
of the kernel, as an additional layer of the operating system.
In DICK, activation and suspension of aperiodic tasks are handled by two primitives,
activate
and
sleep
, which introduce another state, called SLEEP. An aperiodic task
enters the SLEEP state by executing the
sleep
primitive. A task exits the SLEEP state
and goes to the READY state only when an explicit activation is performed by another
task.
Task creation and activation are separated in DICK. The creation primitive (
create
)
allocates and initializes all data structures needed by the kernel to handle the task;
however, the task is not inserted in the ready queue, but it is left in the SLEEP state,
until an explicit activation is performed. This is mainly done for reducing the runtime
overhead of the activation primitive.
The state transition diagram used in DICK is
illustrated in Figure 10.7.
Search WWH ::
Custom Search