VHDL Programming

The VitalPathDelay01procedure has a number of parameters passed

to it. These parameters are used to control what kind of glitch behavior

is wanted, the delays to be used, and the temporary data used to store sig-

nal information.

In this example, the VitalPathDelayprocedure is passed the following

parameters:

OutSignal—The signal to have the new value placed on it.

OutSignalName—The name of the output signal to be used in

glitch reporting or error reporting.

OutTemp—A temporary signal used to store the current value of

the signal for comparison.

Paths—An array used to store delay information. There is a table

entry for each delay arc through the device.

GlitchData—A temporary storage area used to store signal state

and transition information for use in calculating glitches.

Mode—Specifies the type of glitch behavior wanted.

GlitchKind—Specifies the kind of glitches generated,OnEventor

OnDetect.

Flip-Flop Example

In this next section, we examine another VITAL model with more com-

plexity. This example shows the VITAL model for a DFF device. This

device has sequential behavior and needs to have timing checks to check

for illegal timing conditions:

----- CELL DFF -----

library IEEE;

use IEEE.STD_LOGIC_1164.all;

use IEEE.VITAL_Timing.all;

use IEEE.VITAL_Primitives.all;

library alt_vtl;

use alt_vtl.SUPPORT.all;

-- entity declaration --

entity DFF is

generic(

TimingChecksOn: Boolean := True;

XGenerationOn: Boolean := False;

InstancePath: STRING := “*”;

388 Chapter Seventeen