Introduction to HDLs

1
Introduction to HDLs

• HDL (Hardware Description Language)
• VHDL versus Verilog
• IC world only uses Verilog

2
How do IC designers use Verilog?

• Can be used for simulation
• Simulation at behavioral level, gate level, and
  at the switch level!
• Can be used for circuit synthesis
• Can be used to verify post-synthesis timing

3
Why Verilog and not VHDL?

• C-like syntax (as opposed to Pascal-like!)
• Better for circuit synthesis
• I feel it is easier to create testbenches but
  others will dispute this claim!
• Switch-level descriptions supported
• Timing is more easily included
• Can link in you own C-code!

4
Verilog Coding Styles

• Behavioral Descriptions
• Dataflow Descriptions
• Gate-Level Descriptions (netlist)
• Switch-Level Descriptions

5
Verilog Basics

• Case-sensitive!!!!!
• No special characters in variable names except _
• Variable names must start with alpha character
• Free-form
• Very C-like

6
Concurrent Versus Sequential

• Separate syntax to support descriptions of
  concurrent and sequential activity
• Concurrent constructs best for describing
  combinational circuits
• Sequential constructs must be used for describing
  sequential networks and for writing testbenches
  MAY be used for combinational circuits BUT BE
  CAREFUL!

7
First Example
// // First example // module first_example(f, x,
y, z) input x, y, z output f
assign f (x y z) (x y z)
(x y z) endmodule
8
First Example Testbench
// // Testbench for first example // timescale
1ns/100ps module first_example_tb reg
x, y, z wire f integer fid
first_example u0(f, x, y, z) initial
begin fid fopen("./first_example.out")
fmonitor(fid, time, " x b,
y b, z b, f b", x, y, z, f)
100 x 1'b0 y 1'b0 z 1'b0
100 x 1'b1 y 1'b1 z 1'b0
100 x 1'b1 y 1'b1 z 1'b1
100 finish end endmodule
9
Running Verilog XL
To simulate first example do the following
verilog first_example_tb.v first_example.v OR Cr
eate a file called, for example, modules and on
separate Lines place the two filenames from
above and give the Command verilog f modules