Hardware Reference
In-Depth Information
τ
1
0
6
12
18
24
τ
2
0
8
16
24
EDL
ω
(t)
0
1
2
3
4
5
6
7
8
9
10
11
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14
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24
(a)
τ
1
0
6
12
18
24
τ
2
0
8
16
24
aperiodic
requests
0
1
2
3
4
5
6
7
8
9
10
11
12
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24
(b)
a.
Idle times available at time
t
=8
Figure 6.8
under EDL.
b.
Schedule of the aperiodic
request with the EDL server.
The basic idea behind the EDL server is to use the idle times of an EDL schedule to
execute aperiodic requests as soon as possible. When there are no aperiodic activities
in the system, periodic tasks are scheduled according to the EDF algorithm. Whenever
a new aperiodic request enters the system (and no previous aperiodic is still active) the
idle times of an EDL scheduler applied to the current periodic task set are computed
and then used to schedule the aperiodic requests pending. Figure 6.8 shows an example
of the EDL service mechanism.
Here, an aperiodic request with an execution time of 4 units arrives at time
t
=8.
The idle times of an EDL schedule are recomputed using the current periodic tasks, as
shown in Figure 6.8a. The request is then scheduled according to the computed idle
times (Figure 6.8b). Notice that the server automatically allocates a bandwidth 1
−
U
p
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