ModelSim SE User's Manual - Electrical and Computer Engineering

UM-58 3 - Design libraries
Design library overview
Design unit information
ModelSim SE User’s Manual
A design library is a directory or archive that serves as a repository for compiled design
units. The design units contained in a design library consist of VHDL entities, packages,
architectures, and configurations; Verilog modules and UDPs (user-defined primitives);
and SystemC modules. The design units are classified as follows:
Primary design units
Consist of entities, package declarations, configuration declarations, modules, UDPs,
and SystemC modules. Primary design units within a given library must have unique
names.
Secondary design units
Consist of architecture bodies, package bodies, and optimized Verilog modules.
Secondary design units are associated with a primary design unit. Architectures by the
same name can exist if they are associated with different entities or modules.
The information stored for each design unit in a design library is:
retargetable, executable code
debugging information
dependency information
Working library versus resource libraries
Design libraries can be used in two ways: 1) as a local working library that contains the
compiled version of your design; 2) as a resource library. The contents of your working
library will change as you update your design and recompile. A resource library is typically
static and serves as a parts source for your design. You can create your own resource
libraries, or they may be supplied by another design team or a third party (e.g., a silicon
vendor).
Only one library can be the working library. In contrast any number of libraries can be
resource libraries during a compilation. You specify which resource libraries will be used
when the design is compiled, and there are rules to specify in which order they are searched
(see "Specifying the resource libraries" (UM-64)).
A common example of using both a working library and a resource library is one where
your gate-level design and testbench are compiled into the working library, and the design
references gate-level models in a separate resource library.
The library named "work"
The library named "work" has special attributes within ModelSim; it is predefined in the
compiler and need not be declared explicitly (i.e. library work). It is also the library name
used by the compiler as the default destination of compiled design units (i.e., it doesn’t need
to be mapped). In other words the work library is the default working library.