ModelSim SE User's Manual - Electrical and Computer Engineering

Default binding
Simulating VHDL designs UM-79
By default ModelSim performs default binding when you load the design with vsim (CR-
373). The advantage of performing default binding at load time is that it provides more
flexibility for compile order. Namely, entities don't necessarily have to be compiled before
other entities/architectures which instantiate them.
However, you can force ModelSim to perform default binding at compile time. This may
allow you to catch design errors (e.g., entities with incorrect port lists) earlier in the flow.
Use one of these two methods to change when default binding occurs:
Specify the -bindAtCompile argument to vcom (CR-311)
Set the BindAtCompile (UM-527) variable in the modelsim.ini to 1 (true)
Default binding rules
When looking for an entity to bind with, ModelSim searches the currently visible libraries
for an entity with the same name as the component. ModelSim does this because IEEE
1076-1987 contained a flaw that made it almost impossible for an entity to be directly
visible if it had the same name as the component. In short, if a component was declared in
an architecture, any like-named entity above that declaration would be hidden because
component/entity names cannot be overloaded. As a result we implemented the following
rules for determining default binding:
If performing default binding at load time, search the libraries specified with the -Lf
argument to vsim.
If a directly visible entity has the same name as the component, use it.
If an entity would be directly visible in the absence of the component declaration, use it.
If the component is declared in a package, search the library that contained the package
for an entity with the same name.
If none of these methods is successful, ModelSim will also do the following:
Search the work library.
Search all other libraries that ar e currently visible by means of the library clause.
If performing default binding at load tim e, search the libraries specified with the -L
argument to vsim.
Note that these last three searches are an extension to the 1076 standard.
Disabling default binding
If you want default binding to occur only via configurations, you can disable ModelSim’s
normal default binding methods by setting the RequireConfigForAllDefaultBinding (UM-
527) variable in the modelsim.ini to 1 (true).
ModelSim SE User’s Manual