State Dependent Path
Formal Definition
State Dependent Path is a path that occurs only when the condition is met.
Simplified Syntax
if (condition) simple_module_path;
if (condition)
edge_sensitive_path;
ifnone simple_module_path;
Description
Generally, state dependent path is comprised of three parts. A
condition that enables the module path, a module path description and
a delay that applies to the module path.
The condition is an expression using scalars or vectors of any type.
It can also be part-selects or bit-selects of a vector. Constant
numbers and specparams can be used in the condition expression. The
result of the conditional expression can be one bit or multiple bits.
If it is more than one bit, the least significant bit represents the result.
When no edge transition is specified for the inputs, it is called the
simple state-dependent path. Example 1 shows the simple-dependent path.
If any edge transition is specified for the input, then it is called
an edge-sensitive state-dependent path. Different delays can be used
to the same path if the following rules are followed:
-
A declaration must be unique and should use an edge or a conditional
expression or both.
-
The port for which the delay is specified must be referenced in
exactly the same way. You cannot mix part select, bit-select and
complete ports.
Examples
Example 1
module example1 (cond, in_1,
in_2, out);
input in_1, in_2, cond ;
output out ;
and (out, in_1, in_2) ;
specify
specparam TRise1 = 5,
TFall1 = 5,
TRise2 = 7,
TFall2 = 7;
if (cond) ( in_1,
in_2 *> out ) = (TRise1, TFall1);
if (~cond) ( in_1,
in_2 *> out ) = (TRise2, TFall2);
endspecify
endmodule
If a conditional expression 'cond' is true, TRise1
and TFall1 will be assigned
to a path as delays. When the conditional expression 'cond' is false, TRise2
and TFall2 will be used as
the path delays.
Important Notes
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