Icarus Verilog contains a code generator to emit 1995 compliant Verilog from the input Verilog netlist. This allows Icarus Verilog to function as a Verilog > 1995 to Verilog 1995 translator. The main goal of the project was to convert @*, ANSI style arguments and other constructs to something allowed in 1995 Verilog.
This generator is currently only available in development and is not finished!
Invocation[]
To translate a Verilog program to 1995 compliant Verilog, invoke "iverilog" with the -tvlog95 flag.
% iverilog -tvlog95 -o my_design_95.v my_design.v
The generated Verilog will be placed in a single file (a.out by default), even if the input Verilog is spread over multiple files.
Generator Flags[]
| Flag | Description |
|---|---|
| -pspacing=N | Set the indent spacing (the default is 2). |
| -pallowsigned=1 | Allow emitting the various signed constructs as an extension to 1995 Verilog (off by default). |
| -pfileline=1 | Emit the original file and line information as a comment for each generated line (off by default) |
Structures that cannot be converted to 1995 compatible Verilog[]
The following Verilog constructs are not translatable to 1995 compatible Verilog:
- Automatic tasks or functions.
- The power operator (**). Expressions of the form (2**N)**<variable> (where N is a constant) can be converter to a shift.
- Some System Verilog constructs (e.g. final blocks, ++/-- operators, etc.). 2-state variables are converted to 4-state variables.
Icarus extensions that cannot be translated[]
- Integer constants greater than 32 bits.
- Real valued nets.
- Real modulus.
- Most Verilog-A constructs.
Known issues/limitations[]
Some things are just not finished and should generate an appropriate warning. Here is a list of the major things that still need to be looked at.
- There are still a few module instantiation port issues (pr1723367 and partselsynth).
- inout ports are not converted (tran-VP).
- Variable selects of a non-zero based vector in a continuous assignment are not converted.
- There is no support for translating a zero repeat in a continuous assignment. It is currently just dropped.
- A pull device connected to a signal select is not translated correctly (this may be fixed).
- L-value indexed part selects with a constant undefined base in a continuous assignment are not translated.
- Logic gates are not arrayed exactly the same as the input and the instance name is not always the same.
- The signed support does not generate $signed() or $unsigned() function calls in a continuous assignment expression.
- The special power operator cases are not converted in a continuous assignment.
- Currently a signed constant that sets the MSB in an unsigned context will be displayed as a negative value (e.g. bit = 1 translates to bit = -1).
- Can net arrays, etc. be unrolled?
- Can generate blocks be converted?