Hardware Reference
In-Depth Information
1. a is false in clock tick 2 or b is false in clock ticks 3 and 4. In this case, the
sequence has no match.
2. a is true in clock tick 2, b is true in clock tick 3, and b is false in clock tick 4. In
this case, the sequence has a single match at clock tick 3.
3. a is true in clock tick 2, b is false in clock tick 3, and b is true in clock tick 4. In
this case, the sequence has a single match at clock tick 4.
4. a is true in clock tick 2 and b is true in clock ticks 3 and 4. In this case, the
sequence has two matches, or two tight satisfaction points: 3 and 4.
Sequence a ##[1:2] b defines 0, 1, or 2 trace fragments. In case 1 it defines
zero fragments, in case 2 it defines one fragment, 2:3, in case 3 it also defines one
fragment, 2:4, and in case 4 it defines two fragments, 2:3. and 2:4.
t
In this chapter, we use the following conventions: letters a ,..., e denote Boolean
expressions, r and s denote sequences, and p and q denote properties. We numerate
clock ticks with integer numbers starting with 0. In diagrams, we designate trace
fragments defined by sequence matches with ovals.
The sequence and property operators described in this chapter are summarized in
Table 6.1 . They are grouped by their precedence, from highest to lowest. Additional
sequence operators are covered in Chap. 11 .
6.1
Boolean Sequence
Boolean expression e defines the simplest sequence—a Boolean sequence .This
sequence has a match (or a tight satisfaction point) at its initial point if e is
true. Otherwise, it does not have any satisfaction points at all. This is illustrated
in Fig. 6.1 .
Example 6.2.
The initial fragment of the trace of signals a and b is shown in
Table 6.2 .
Table 6.1 Basic sequence
and property operators
Operator Associativity
[ * ...] -
[ * ]
-
-
[+]
Left
##
Left
or
Right
|->
Right
|=>
e
clock ticks
Fig. 6.1
Boolean sequence
 
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