This file is designed to help users become familiar with the
UserDefinedSchematic interface and how to create custom glyphs for
circuits.  

In order to create a userdefined schematic, two things are required.
first, your class must implement the interface UserDefinedSchematic.
This interface contains a single method that you must overload called
paint.  Here is some code showing how this is used

// alu32bit.java
// 7/21/98
// Tim Wheeler
// Purpose: The 32-bit alu used in the MIPS processor

// These are needed for circuit construction and simulation
import byucc.jhdl.base.*;
import byucc.jhdl.Logic.*;
import byucc.jhdl.Xilinx.XC4000.*;
import byucc.jhdl.Xilinx.XC4000.carryLogic.*;
import Schematic.*;

// This is the 32-bit alu.  It instantiates 16 2-bit alu modules and combines
//   them with other logic to make thet 32-bit alu.  It extends Logic, which is
//   similar to Structural, but with added functionality.
public class alu32bit extends Logic implements UserDefinedSchematic {

  ////////// Global declarations /////////////////////////////////////////////
  // Port interface, which is necessary in all modules except the testbench
  public static final String[]
    portnames = 
    {    "i0",    "i1", "aluop", "result",  "cout",  "zero" }, 
    portwidths = 
    {    "32",    "32",     "3",    "32",     "1",     "1" }, 
    portios = 
    {    "in",    "in",    "in",   "out",   "out",   "out" };
  public String cellname = "ALU32BIT";

  ////////////////////////////////////////////////////////////////////////////

    public void paint( UserDefinedNode udn ) {
	udn.setSize( 40, 60 );
	udn.drawLine( 0, 0, 0, 20 );
	udn.drawLine( 0, 20, 5, 25 );
	udn.drawLine( 5, 25, 0, 30 );
	udn.drawLine( 0, 30, 0, 50 );
	udn.drawLine( 0, 50, 40, 40 );
	udn.drawLine( 40, 40, 40, 10 );
	udn.drawLine( 40, 10, 0, 0 );
	udn.drawLine( 20, 45, 20, 60 );
	udn.drawLine( 7, 25, 17, 25 );
	udn.drawLine( 12, 20, 12, 30 );


	udn.addInPort( 0, 10, "i0" );
	udn.addInPort( 0, 40, "i1" );
	udn.addInPort( 20, 60, "aluop" );
	udn.addOutPort( 40, 25, "result" );
	udn.addOutPort( 40, 15, "cout" );
	udn.addOutPort( 40, 35, "zero" );

    }



UserDefinedNode, the object passed into the paint routine, contains a
number of methods that will allow the user to create their own
schematic.  

public void drawLine( int x1, int y1, int x2, int y2 )

this draws a line from point 1 to point 2


public void drawRect( int x, int y, int width, int height )

this creates a rectangle where the upper left corner is located at (x,y) 


public void drawArc( int x, int y, int width, int height, int startAngle, int rotateAngle ) 

this draws an arc inside of a rectangle specified by the first 4
arguments.  the startAngle argument specifies where the arc will
start.  0 is pointing to the right and it rotates clockwise.  (i.e. 90
is pointing down ).  the rotate angle specifies how many degress to
rotate the arc in the clockwise direction.  ( 360 for rotateAngle will
create a circle or ellipse )


public void drawText( int x, int y, String text )

draws text at (x,y) (*note portnames and cellname is automatically
added)


public void setSize( int width, int height ) 

sets the size of the glyph


public void addInPort( int x, int y, String name )

places the in port specified by name at location (x,y)


public void addOutPort( int x, int y, String name )

places the out port specified by name at location (x,y)


public void addCellName( String name ) 

changes default cell name to name.  If this function is not called the
schematic will use the name specified by the instance.