Hardware Reference
In-Depth Information
Theorem 4.6
A set of synchronous periodic tasks with relative deadlines less than or
equal to periods can be scheduled by EDF if and only if
U<
1
and
∀
t
∈D
dbf
(
t
)
≤
t.
(4.29)
where
min[
H,
max(
D
max
,L
∗
)]
D
=
{
d
k
|
d
k
≤
}
and
i
=1
(
T
i
−
D
i
)
U
i
L
∗
=
.
1
−
U
EXAMPLE
To illustrate the processor demand criterion, consider the task set shown in Table 4.4,
where three periodic tasks with deadlines less than periods need to be guaranteed under
EDF. From the specified parameters it is easy to compute that
2
6
+
2
8
+
3
=
11
12
U
=
9
i
=1
(
T
i
−
D
i
)
U
i
L
∗
=
=25
1
−
U
H
=
lcm(6
,
8
,
9) = 72
.
y = L
G(0,L)
g(0,L)
L
L
*
Figure 4.19
Maximum value of
L
for which the processor demand test has to be verified.
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