190 Chapter Seven
generics have been mapped in the architecture. The configuration can be
specified as shown in the following:CONFIGURATION decode_gen_con2 OF decode IS
FOR structural
FOR i1, i2 : inv USE ENTITY WORK.inv(inv_gen);
END FOR;FOR a1, a2, a3, a4 : and3 USE ENTITY
WORK.and3(and3_gen);
END FOR;
END FOR;
END decode_gen_con2;The lower-level configuration cannot specify values for the generics if
the architecture has mapped values to the generics in the architecture.Generic Specifications in Configurations
The method of specifying generic values with the most flexibility is to
specify generic values in the configuration for the entity. This method
allows the latest binding of all the methods for specifying the values for
generics. Usually, the later the values are specified, the better. Late binding
allows back-annotation of path delay generics to occur in the configuration.
For instance, there are a number of steps involved in the design of an
ASIC. Following are the steps required:1.Create the logic design model of a device.2.Simulate the model.3.Add estimated delays to device model.4.Simulate model.5.Create physical layout of the model.6.Calculate physical delays from the layout.7.Feed back physical delays to the device model.8.Resimulate using actual delays.The process of feeding back the physical delays into the model can be
accomplished by modifying the architecture or by creating a configuration