From: Adam Krolnik (adamk@cyrix.com)
Date: Tue Jan 12 1999 - 06:46:59 PST
[ACK - Delete optional filename argument in line directive.
Used compilation_constant_expression for `if directive.
Described use of `endif with `if. {There is no
corresponding discussion of the requirement of `endif
with `ifdef in the current LRM.}
Updated this proposal with addition
of mandatory level parameter in `line directive.]
B29: Line and File compiler directive.
The C preprocessor (cpp) is the model of the preprocessor that the Verilog
language uses. Currently there are several directives in 'cpp' that are not
present in the Verilog definition. These directives are:
`ifndef `line `if `elif
The directive `ifndef is already accepted for addition. The remainder are the
subject of this proposal. The current proposal asks for the `line directive
this proposal extends this to add `if and `elif.
Justifications:
The line number compiler directive is useful for source to source translators
to reflect original file/line numbers to the compiler for future reference
to the original source code. In order for this information to be useful there
must be a single syntax to accept this information in order to properly
report it.
The `if and `elif compiler directives are proposed for consistency with
the C language preprocessor. They showed use to include in the C definitions
and are useful to extend conditional compilation selection. These additional
directives will simplify complex conditional compilation setup.
Proposal:
Add section 16.7, `line
The line number (`line) compiler directive is used to reset the current line
number of the current file to the arguments presented. This can be used to
reflect the line number and file name of the original file - if the actual
source file has been modified by addition of lines. After specifying
the new line number or file name, the compiler can correctly refer to
the original source file location for example error messages, source code
debugging, etc.
The syntax for the 'line compiler directive is given in Syntax 16-X.
line_compiler_directive ::=
`line number "filename" level
The directive can be specified anywhere within the Verilog HDL source
description. The number is the new line number of the next line. The
filename is the new name of the file. The filename can be a full or
relative path name. The level indicates whether you have entered
(value is 1) an include file, exited (value is 2) an include file
or (value is 0) have done neither.
Add section 16.5 `if `elif
These conditional compilation directives are used to include optional lines
of Verilog HDL source description during compilation. The `if compiler
directive evaluates the given expression. The syntax for the directives is
given in Syntax 16-X.
if_compiler_directive ::=
`if compilation_constant_expression
elif_compiler_directive ::=
`elif compilation_constant_expression
If the compilation_constant_expression evaluates to a non-zero value then
the following source code lines are included for compilation. If the
expression evaluates to zero and an `else directive exists then the
source code following the `else directive is included for
compilation. The `elif compiler directive is a shortened form of the two
sequential directives `else and `if and has the same functionality.
The `elif directive must follow a text region that is controlled by an
`if or an `elif directive. Each `if directive requires a `endif directive to
enclose the text region. It may be after the text region or after the
text region of the corresponding `else or `elif directive. Nested `if
directives do require matching nested `endif directives.
The expression evaluated by the `if and `elif compiler directives may
include any of the verilog operators (unary, binary, ternary) and the
additional "defined" unary operator. This additional operator provides
the same functionality as the `ifdef compiler directive. This operator
returns zero if the subsequent preprocessor value is not defined with
a value. It returns non-zero if the preprocessor value is defined.
The syntax of the "defined" unary operator is the following:
unary_defined ::= defined preprocessor-symbol
The preprocessor-symbol is a symbol that may or may not have been defined
using the 'define compiler directive.
<p><p><p> Adam Krolnik
Verification Engineer
Cyrix - NSC.
Richardson TX. 75085
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