What is Ifdef in System Verilog?
What is Ifdef in System Verilog?
The keyword `ifdef simply tells the compiler to include the piece of code until the next `else or `endif if the given macro called FLAG is defined using a `define directive.
What is a compiler directive like include and Ifdef?
`include. The `include compiler directive lets you insert the entire contents of a source file into another file during Verilog compilation. The compilation proceeds as though the contents of the included source file appear in place of the `include command.
Can Ifdef be nested?
#ifdef directives can be nested, however, all directives in a given logical level must exist in a single file. The following sample code showing use of the #ifdef directive chain with nested #ifdefs.
What are text macros in Verilog?
What is a macro? The term ‘macro’ refers to the substitution of a line or a few lines of text code. The directive “`define” creates a macro for substitution code. Once the macro is defined, it can be used anywhere in a compilation unit scope, wherever required.
How do you define a constant in Verilog?
In Verilog-1995[6], there are two ways to define constants: the parameter, a constant that is local to a module and macro definitions, created using the `define compiler directive. A parameter, after it is declared, is referenced using the parameter name.
Is a preprocessor directive which is used to end the scope of #ifdef?
If the particular identifier is defined, the statements following this preprocessor directive are executed till another preprocessor directive #endif is encountered. #endif is used to end the scope of #ifdef.
What does Ifdef mean?
#ifdef: This directive is the simplest conditional directive. This block is called a conditional group. The controlled text will get included in the preprocessor output iff the macroname is defined. The controlled text inside a conditional will embrace preprocessing directives.
How many arguments macro can have?
For portability, you should not have more than 31 parameters for a macro. The parameter list may end with an ellipsis (…).
What does the ifdef keyword DO in Verilog?
The keyword `ifdef simply tells the compiler to include the piece of code until the next `else or `endif if the given macro called FLAG is defined using a `define directive. `ifdef < FLAG > `endif `ifdef < FLAG > `else `endif `ifdef < FLAG1 > `elsif < FLAG2 > `elsif < FLAG3 > `else `endif
What are the conditional compiler directives in Verilog?
Verilog has following conditional compiler directives. The `ifdef compiler directive checks for the definition of a text_macro_name. If the text_macro_name is defined, then the lines following the `ifdef directive are included. If the text_macro_name is not defined and an `else directive exists, then this source is compiled.
How does the ifdef compiler check a source?
The `ifdef compiler directive checks for the definition of a text_macro_name. If the text_macro_name is defined, then the lines following the `ifdef directive are included. If the text_macro_name is not defined and an `else directive exists, then this source is compiled.
What happens when an ifdef is evaluated to be false?
If an #ifdef is evaluated to be false, then the #elseif directive is processed as if it was an #ifdef directive. If all #elseif directives evaluate to be false, the #else directive is processed if it exists. Input is evaluated until an #endif directive is encountered.