This is an excerpt from the Chapter 1 of the book
Principles of Verilog PLI by Swapnajit Mittra
published from Kluwer Academic Publishers. ISBN: 0-7923-8477-6
[All copyright reserved. No portion of this text can be used for
for commercial purpose without explicit permission from
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PLI - A QUICK TOUR
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FOUR STEPS FOR WRITING A PLI ROUTINE
Traditionally, the main body of a PLI code is written in a file,
which is called veriuser.c by convention. Though this name is completely
user-defined, but while making a script for the compilation in Verilog
XL, the vconfig tool will assume this name by default (We will discuss
about this later in this chapter). For our discussion, we will assume that
our PLI routine will be saved in the file veriuser.c.
To illustrate the basic steps for creating a PLI routine, the
following problem is taken. This problem is much simplified compared to
the actual 'real life' problems solved using PLI. However, this example
shows all the basic steps that are required in all PLI routines.
Create a system call $print_reg which takes a register as parameter
and prints its value. (This is a simplified version of $display).
As an example, a verilog program like this:
reg [3:0] r1;
r1 = 4'ha;
#100 r1 = 4'h3;
Should produce the values 10 and 3 at times 100 and 300.
The following are the steps for writing a PLI routine.
Step 1 of 4: Including the header files
The file veriuser.c containing the main PLIC program must
in Verilog XL and
As always in C, a header file within corner brackets (i.e. '<'
and'>') means during the compilation the file should be either in the /usr/include
directory or in a path include_path_name. In the later case, however,
the program must be compiled with -Iinclude_path_name option. The
include files can also be specified as shown below.
A typical example of include_path_name may look like /usr/caetools/verilog/.../include
The header file(s) contains the most basic data-structures of the Verilog-PLI
that the program will use.
Step 2 of 4: Function prototype and Variable declaration
This part of the program contains all local variables and the
functions that it invokes as part of the system call. In the present case,
as explained in the next step, it will be as shown below.
int my_calltf(), my_checktf();
However, if the functions are in separate files, they sould be declared
as external functions.
extern int my_calltf(), my_checktf();
A typical PLI code, like any other C program, may need few other housekeeping
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