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geda:icarus_anc [2012/02/20 15:14] (current)
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 +====== Icarus Attribute Naming Conventions ======
 +Attributes that are specific to Icarus Verilog, and are intended to be
 +of use to programmers,​ start with the prefix "​ivl_"​.
 +Attributes with the "​_ivl_"​ prefix are set aside for internal
 +use. They may be generated internally by the compiler. They need not
 +be documented here.
 +The following is a summary of Verilog attributes that Icarus Verilog
 +understands within Verilog source files to control synthesis
 +behavior. This section documents generic synthesis attributes. For
 +target specific attributes, see target specific documentation.
 +These attributes only effect the behavior of the synthesizer. For
 +example, the ivl_combinational will not generate an error message
 +if the Verilog is being compiled for simulation. (It may generate a
 +* Attributes for "​always"​ and "​initial"​ statements
 +(* ivl_combinational *)
 +    This attribute tells the compiler that the statement models
 +    combinational logic. If the compiler finds that it cannot make
 +    combinational logic out of a marked always statement, it will
 +    report an error.
 +    This attribute can be used to prevent accidentally inferring
 +    latches or flip-flops where the user intended combinational
 +    logic.
 +(* ivl_synthesis_on *)
 +    This attribute tells the compiler that the marked always statement
 +    is synthesizable. The compiler will attempt to synthesize the
 +    code in the marked "​always"​ statement. If it cannot in any way
 +    synthesize it, then it will report an error.
 +(* ivl_synthesis_off *)
 +    If this value is attached to an "​always"​ statement, then the
 +    compiler will *not* synthesize the "​always"​ statement. This can be
 +    used, for example, to mark embedded test bench code.
 +* Attributes for modules
 +(* ivl_synthesis_cell *)
 +    If this value is attached to a module during synthesis, that
 +    module will be considered a target architecture primitive, and
 +    its interior will not be synthesized further. ​ The module can
 +    therefore hold a model for simulation purposes.
 +* Attributes for signals (wire/​reg/​integer/​tri/​etc.)
 +(* PAD = "<​pad assignment list>"​ *)
 +    If this attribute is attached to a signal that happens to be a
 +    root module port, then targets that support it will use the string
 +    value as a list of pin assignments for the port/​signal. The format
 +    is a comma separated list of location tokens, with the format of
 +    the token itself defined by the back-end tools in use.
 +* Other Attributes
 +[ none defined yet ]
 +(* _ivl_schedule_push *)
 +    If this attribute is attached to a thread object (always or
 +    initial statement) then the vvp code generator will generate code
 +    that causes the scheduler to push this thread at compile time. The
 +    compiler may internally add this attribute to always statements if
 +    it detects that it is combinational. This helps resolve time-0
 +    races.</​code>​
geda/icarus_anc.txt ยท Last modified: 2012/02/20 15:14 (external edit)