Library usage

All modules and UDPs in a Verilog design must be compiled into one or more libraries. One library is usually sufficient for a simple design, but you may want to organize your modules into various libraries for a complex design. If your design uses different modules having the same name, then you are required to put those modules in different libraries because design unit names must be unique within a library.

The following is an example of how you may organize your ASIC cells into one library and the rest of your design into another:

% vlib work
% vlib asiclib
% vlog -work asiclib and2.v or2.v
-- Compiling module and2
-- Compiling module or2 
Top level modules:
	and2
	or2
% vlog top.v
-- Compiling module top 
Top level modules:
	top 

Note that the first compilation uses the -work asiclib option to instruct the compiler to place the results in the asiclib library rather than the default work library.

Since instantiation bindings are not determined at compile time, you must instruct the simulator to search your libraries when loading the design. The top level modules are loaded from the library named work unless you specify an alternate library with the -lib option. All other Verilog instantiations are resolved in the following order:

• Search libraries specified with -Lf options in the order they appear on the command line.
• Search the library specified in the "Verilog-XL `uselib compiler directive" .
• Search libraries specified with -L options in the order they appear on the command line.
• Search the work library.
• Search the library explicitly named in the special escaped identifier instance name.

It is important to recognize that the work library is not necessarily a library named work - the work library refers to the library containing the module that instantiates the module or UDP that is currently being searched for. This definition is useful if you have hierarchical modules organized into separate libraries and if sub-module names overlap among the libraries. In this situation you want the modules to search for their sub-modules in the work library first. This is accomplished by specifying -L work first in the list of search libraries.

For example, assume you have a top level module "top" that instantiates module "modA" from library "libA" and module "modB" from library "libB". Furthermore, "modA" and "modB" both instantiate modules named "cellA", but the definition of "cellA" compiled into "libA" is different from that compiled into "libB". In this case, it is insufficient to just specify "-L libA - L libB" as the search libraries because instantiations of "cellA" from "modB" resolve to the "libA" version of "cellA". The appropriate search library options are "-L work -L libA -L libB".

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