ModelSim SE User's Manual - Electrical and Computer Engineering

UM-116 5 - Verilog simulation
ModelSim SE User’s Manual
Note that the compiler lists each module as a top level module, although, ultimately, only
top is a top-level module. If a module is not referenced by another module compiled in the
same invocation of the compiler, then it is listed as a top level module. This is just an
informative message and can be ignored during incremental compilation. The message is
more useful when you compile an entire design in one invocation of the compiler and need
to know the top-level module names for the simulator. For example,
% vlog top.v and2.v or2.v
-- Compiling module top
-- Compiling module and2
-- Compiling module or2
Top level modules:
top
Automatic incremental compilation with -incr
The most efficient method of incremental compilation is to manually compile only the
modules that have changed. However, this is not always convenient, especially if your
source files have compiler directive interdependencies (such as macros). In this case, you
may prefer to compile your entire design along with the -incr argument. This causes the
compiler to automatically determine which modules have changed and generate code only
for those modules.
The following is an example of how to compile a design with automatic incremental
compilation:
% vlog -incr top.v and2.v or2.v
-- Compiling module top
-- Compiling module and2
-- Compiling module or2
Top level modules:
top
Now, suppose that you modify the functionality of the or2 module:
% vlog -incr top.v and2.v or2.v
-- Skipping module top
-- Skipping module and2
-- Compiling module or2
Top level modules:
top
The compiler informs you that it skipped the modules top and and2, and compiled or2.
Automatic incremental compilation is intelligent about when to compile a module. For
example, changing a comment in your source code does not result in a recompile; however,
changing the compiler command line arguments results in a recompile of all modules.
Note: Changes to your source code that do not change functionality but that do affect
source code line numbers (such as adding a comment line) will cause all affected
modules to be recompiled. This happens because debug information must be kept current
so that ModelSim can trace back to the correct areas of the source code.