TABLE OF CONTENTS In this chapter we look at the facilities in VHDL for file input and output. Files serve a number of purposes, one of which is to provide long-term data storage. In this context, "long-term" means beyond the lifetime of one simulation run. Files can be used to store data to be loaded into a model when it is run, or to store the results produced by a simulation. VHDL also provides specialized versions of file operations for working with text files. We show how textual input and output can be used to extend the user interface of a simulator with model-specific operations.
We start our discussion of files by looking at the general-purpose mechanisms provided in VHDL for file input and output. VHDL provides sequential access to files using operations, such as "open", "close", "read" and "write", that are familiar to users of conventional programming languages.
A VHDL file is a class of object used to store data. Hence, as with other classes of objects, we must include file-type definitions in our models. The syntax rule for defining a file type is
file_type_definition <span class="unicode">?</span> <b class="bold">file of</b> type_mark
A file-type definition simply specifies the type of objects to be stored in files of the given type. For example, the type declaration
<b class="bold">type</b> integer_file <b class="bold">is file of</b> integer;
defines integer_file to be a type of file that can only contain integers. A file can only contain one type of object, but that type can...
