Hardware Reference
In-Depth Information
τ
2
killed
τ
1
τ
new
τ
2
time overflow
τ
3
0
2
4
6
8
10
12
14
16
18
20
22
24
Figure 10.4
The effects of
τ
2
do not cancel at the time it is aborted, but protract till the
end of its period.
τ
2
killed
τ
1
τ
new
zombie
τ
2
τ
3
0
2
4
6
8
10
12
14
16
18
20
22
24
Figure 10.5
The new task set is schedulable when
τ
new
is activated at the end of the
period of
τ
2
.
said to be in a ZOMBIE state, since it does not exist in the system, but it continues to
occupy processor bandwidth. Figure 10.5 shows that the task set is schedulable when
the activation of
τ
new
is delayed until the end of the current period of
τ
2
.
A more complete state transition diagram including the states described above (DE-
LAY, RECEIVE, and ZOMBIE) is illustrated in Figure 10.6. Note that at the end of its
last period, a periodic task (aborted or terminated) leaves the system completely and
all its data structures are deallocated.
In order to simplify the description of DICK, the rest of this chapter only describes the
essential functions of the kernel. In particular, the message passing mechanism and
the delay primitive are not considered here; as a consequence, the states RECEIVE
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