Testbenches

TESTBENCHES

 Synthesis our design, from the source window select, Synthesis/ implementation from the window Now double click the Synthesis –XST.

 After the HDL synthesis phase of the synthesis process, you can display a schematic representation of our synthesized source file.

§   This schematic shows a representation of the pre-optimized design in terms of generic symbols, such as adders, multipliers, counters, AND gates, and OR gates àdouble click View RTL Schematic.

§   Double click the schematic to internal view.

§   Double click outside the schematic to move one-level back.

§   This schematic shows a representation of the design in terms of logic elements optimized to the target device.

§   For example, in terms of LUTs(Look Up Table), carry logic, I/O buffers, and other technology-specific components à Double click View Technology Schematic.

§   Double click the schematic to inner view.

§   Double click the LUT to inner view. This is Gate Level view of LUT, if we want see Truth Table and K-Map for our design just click the respective tabs.

§   After finishing the synthesis, we can view number of Slices, LUT (Look Up Table), I/Os are taken by our deign in Device using Design summary.

Example MUX Description Using Case Statement

module mux4 (s a, b, c, d, y);

input [1:0] s;

input [1:0] a, b, c, d;

output [1:0] y;

reg [1:0] y;

always @(s or a or b or c or d)

begin case (s)

2'b00: y = a;

2'b01: y = b;

2'b10: y = c; default:y = d; endcase

endendmodule

The preceding Case statement will evaluate the values of the input s in priority order. To avoid priority processing, it is recommended that you use a parallel-case Verilog meta comment which will ensure parallel evaluation of the sel inputs as in the following.

Example:

always @(sel or a or b or c or d) //synthesis parallel_case

For and Repeat loops

When using always blocks, repetitive or bit slice structures can also be described using the "for" statement or the "repeat" statement.

The "for" statement is supported for:

 Constant bounds

 Stop test condition using operators <, <=, > or >=

 Next step computation falling in one of the following specifications:

o var = var + step

o var = var – step

(wherevar is the loop variable and step is a constant value).

The repeat statement is only supported for constant values. The following example shows the use of a

For Loop.

Example For Loop Description

modulecountzeros (a, Count); input [7:0] a;

output [2:0] Count; reg [2:0] Count;

reg [2:0] Count_Aux; integer i;

always @(a) begin

Count_Aux = 3'b0;

for (i = 0; i < 8; i = i+1) begin

if (!a[i])

Count_Aux = Count_Aux+1; end

Count = Count_Aux;

endendmodule