Hardware Reference
In-Depth Information
dt
b
e
3
=
0E39h
e
2
=
EAABh
FFFF 0000
e
1
dt
a
Figure 12.1
Circular timer implementation in ERIKA Enterprise.
The main property of the
operator is that
[0
,
2
n
∀
a, b
∈
−
1]
unsigned
(
b
a
)=
dist
(
a, b
)
where
dist
(
x, y
) is the distance from
x
to
y
evaluated on the time circle in the direction
of increasing time values. Note that
dist
(
x, y
)=
d
means that if
t
=
x
then,
after a delay of
d
,wehave
t
=
y
, independently from the fact that
x
and
y
belong
to two different cycles.
unsigned
(
x
) is the value of
x
, interpreted as an
n
-bit unsigned value. We recall
that according to the 2's complement representation,
unsigned
(
x
)=
x
if
x
≥
0
2
n
+
x
otherwise
For example, when evaluating the two events
e
2
and
e
3
in Figure 12.1, we have that
dt
a
=(
e
2
−
e
3
)=
DC
72
H>
8000
H
=
P/
2. Hence, we conclude that
e
2
must
precede
e
3
and that the actual time difference between the events is
dt
b
=(
e
3
−
e
2
)=
238
EH < P/
2.
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