Hardware Reference
In-Depth Information
Fig. 6.5
##3 s
s
clock ticks
Solution:
Let the initial point of the sequence be clock tick i . Sequence
a ##1 b
has a match iff
a
is true in clock tick i and
b
is true in clock tick i
C
1.Thematch
of sequence
a ##1 b
happens in clock tick i
C
1. Therefore, for the fusion to have
a match, sequence
c ##1 d
should have a match starting from clock tick i
C
1.
It means that
c
should be true in clock tick i
C
1, and
d
should be true in clock tick
i
C
2. Bringing it all together, we have that sequence
(a ##1 b) ##0 (c ##1 d)
is equivalent to sequence
a ##1 b && c ##1 d
.
t
Example 6.14.
Write a sequence describing two back-to-back transactions. The
transactions are represented with sequences
trans1
and
trans2
.
Solution:
Consider two interpretations:
trans2
starts in the clock tick when
trans1
finishes.
trans2
starts in the clock tick next to the endpoint of
trans1
.
The first scenario may be expressed as
trans1 ##0 trans2
, while the second
scenario may be expressed as
trans1 ##1 trans2
.
t
We will provide more examples of sequence fusion in the following sections.
6.3.4
Initial Delay
We will start this section with a motivational example:
Example 6.15.
Skip n>0cycles before matching sequence
s
.
Solution:
1 ##n s
. Recall that value 1 means true, matching anything at the initial
clock tick of the resulting sequence.
t
The situation described in Example
6.15
is typical, and for convenience there is
a special syntax to specify the number of clock ticks to be skipped before beginning
a sequence match (Fig.
6.5
), i.e., to specify
initial sequence delay
:
##n s
. The delay
is the number of clock ticks and must be a nonnegative elaboration time integral
constant. Our definition works for nonzero
n
. The case of
n
D
0 is considered in
Sect.
6.9
.
Efficiency Tip.
Large initial delays are inefficient in FV, and may also negatively
affect simulation performance. See Sect.
19.3
for details.
Example 6.16.
The value of
a
should be always true starting from clock tick 2.
Search WWH ::
Custom Search