Advanced Topics 229
If we are not at the end of the file, the process reads in a line from the file
into variable aline.
Successive reads on variable alineretrieve the appropriate fields from
the line. All of the reads return the value into internal variables, but vari-
ables asrcand adstare not really needed because there exists a TextIO
procedure for reading integer values. Variable ainstris used to allow the
string read in to be converted into the enumerated type t_instrbefore
being assigned to the output port instr.SUMMARY
In this chapter we discussed the following:Overloading functions, arguments, operators to make VHDL
models more readable.How aliases can be used to name sections of an object.How qualified expressions are used to direct conversion.How user-defined attributes can be used to add information to
objects.How generate statements can be used to replicate entity
instantiations.How TextIO is used to read and write text files.This chapter showed some of the more esoteric features of VHDL. This
chapter concludes the discussion of VHDL features. The next two chapters
concentrate on the synthesis process and how to write VHDL for
synthesis. The next few chapters then guide the reader through a top-
down description of a device.