This document discusses Verilog tasks. It explains that tasks can be used to encapsulate reusable code and can contain delays, wait statements, and event controls. Tasks can take inputs, outputs, and inouts, and can call other tasks and functions. The definition of a task does not use parentheses or specify ports like modules do. Tasks are invoked by name like regular procedural code and have access to all data objects. The document provides examples of defining and calling tasks to apply stimulus and test a module.

1. 1
Verilog HDLVerilog HDL
ASIC DESIGN USING
FPGA
BEIT VII
KICSIT
Sept 24 2012 Lecture 12

2. 2
Tasks
Sept 24 2012
• In Verilog, you may use a task to encapsulate a
behavior.
• It is defined in a module.
• It is invoked when its name is called in the
procedural code.
• It has access to all data objects, so it does not
need inputs, outputs, though it can have inputs,
outputs and inouts.
Lecture 12

3. 3
Tasks
Sept 24 2012
• You can use the task statement to structure your
Verilog code so that a portion of code is reusable.
• Task may take more than zero time to
complete ; they can have delays (#), wait
statements and event controls (@) in them.
• Task may call other Tasks and Functions.
Lecture 12

4. 4
Tasks
Sept 24 2012
• The definition of a task is the following:
task <task name>; // Notice:
no parameter list or ()s
<argument ports>
<declarations>
<statements>
endtask
•An invocation of a task is of the following form:
<name of task> (<port list>);Lecture 12

5. 5
Tasks
Sept 24 2012
• Tasks can be used to apply stimulus;
module hello_tsk ;
initial begin
say_hello ; // Task
say_hello ; // Task
end
task say_hello;
$display(“ Hello Verilog Tasks! ”) ;
endtask
endmodule
Lecture 12

6. 6
Tasks
Sept 24 2012
module test_adder_t3;
reg [7:0] a, b;
reg cin;
wire [7:0] sum, sum_chk;
wire cout, cout_chk;
// RTL Instance
adder adder_inst(a, b, cin, sum, cout);
//Model instance
adder_model adder_model_inst(a,b,cin,sum_chk,cout_chk);
initial begin
test_design(0, 0, 0); // Task
test_design(0, 1, 1); // Task
test_design(10, 34 1); // Task
test_design(150, 85, 0); // Task
end Lecture 12

7. 7
Tasks
Sept 24 2012
task test_design;
input [7:0] ax, bx;
input cx;
begin
a = ax; b = bx; cin = cx;
#50 if(sum !== sum_chk || cout !== cout_chk)
begin
$display(“ERROR: Sum is wrong");
$stop;
end
end
endtask
endmodule
Lecture 12

8. 8
Tasks
Sept 24 2012 Lecture 12