Creating a core component offers the advantages of design reuse and design security. The design of the core component can be captured in schematic and VHDL and then synthesized to create the EDIF model. EDIF stands for Electronic Design Interchange Format and EDIF models store electronic netlists.
From the core project, you can also generate a new schematic symbol of the core component. By adding different configurations to the core project, the core component can then be used with different FPGA devices.

Creating a Core Project and Schematic

This tutorial is based around the creation of a core component for decoding the keypad on the NanoBoard-NB1.

1. Create a new core project by selecting File » New » Project » Core Project. Save the core project as KeyPadScanner.PrjCor, making sure the project name has no spaces in it.
2. Create or add the schematic that you wish to use as the core to the core project, e.g. KeyPadScanner.SchDoc, shown below in Figure 1. This schematic is available from the \Examples\NB1 Examples\Processor Examples\I2C DAC and ADC
   This example schematic is now, as of ~'AD Summer 09', at this location (....Examples\Soft Designs\Legacy\NB1\EX16)
   - TSK165B folder of the installation. Note that the top sheet of the core design must be the same as the core project name.
   To add this schematic to your core project, right-click on the project name in the Projects panel and select Add Existing to Project. Choose the schematic file, KeyPadScanner.SchDoc, and click Open. The schematic document is added to the project and appears in the Projects panel under Source Documents. Save the project.
   
   
   Figure 1. KeyPadScanner.SchDoc

1. Now we need to set up the project options. Select Project » Project Options and click on the Options tab of the Options for Core Project dialog.
   
   Make sure the Include models in published archive option is selected. This will bundle all EDIF files generated for the core component together in a zip file when you 'publish' the core later. Click OK.
2. For these EDIF files to be generated, a User EDIF models folder must be created. In Microsoft Windows, create a folder, for example MyCores, which will hold your EDIF models. Whenever you synthesize any design, this folder is searched for models, along with the standard system EDIF folders (\Library\EDIF).
3. Now we need to specify this new folder name in the FPGA
   - Synthesis page of the Preferences dialog (Tools » FPGA Preferences) so the system knows where to look for your published EDIF files during synthesis.
   Click on the folder icon next to the Use presynthesized model folder option to browse to the folder's location, as shown in the dialog below. Click OK.
   

Creating Configurations and Constraints

The next setup required is the creation of configuration and constraint files targeting the devices you want your core component to be used on. A constraint file will set the target FPGA device. Note that you need to create one configuration for each device family that you want the core to target. The core component can then be used in any device in that device family. We will set up two configurations so the core component can be used with two different target FPGA device families.
To create a new constraint file:

1. Right-click on the core project name in the Projects panel and select Add New to Project » Constraint File. A Constraint file will appear in the Settings\Constraint Files folder in the Projects panel and a new file, Constraint1.Constraint, opens in the Constraint editor.
   
2. From the Constraint editor menus, select Design » Add/Modify Constraint » Part. The Choose Physical Device dialog appears.
   
3. We will set up a constraint file to target the Xilinx SpartanIIE chip first. Click on Xilinx in the Vendors list and select Spartan2E. The SpartanIIE included with the NanoBoard-NB1 is a 208 pin Quad Flat Pack package, with 300,000 equivalent gates. Click on the cell that represents this device, i.e. the 146 at the junction of XC2S300E and PQ208 for a XC2S300E-6PQ208. Click OK and a new device specification constraint is added into the Constraint file.
   
4. Save the constraint file as Xilinx_Spartan2E.Constraint.
5. Create another constraint file, called Altera_Cyclone.Constraint using steps 1-2 for the Altera Cyclone, 240 pin quad flat pack, 450,000 gate (12k Logic Elements) device (EP1C12). Save and close the constraint files.
6. To assign constraint files to a project, you must create a configuration for each unique output that you intend to generate. Add a configuration and constraints file to the core project by selecting Project » Configuration Manager. Add a Configuration named Xilinx_Spartan2E by clicking on the Add button (next to Configurations) and click OK. Select the configuration check box.
7. Add another configuration called Altera_Cyclone and select the configuration checkbox to match the constraint file.

1. Click OK. Close the constraint files. Save the core project.

Synthesizing the Configurations

Next, we need to synthesize all the configurations that we have just set up.

1. From the Schematic Editor, select Design » SynthesizeAll Configurations to synthesize the core project, i.e. generate the intermediate VHDL files from the schematic(s) and then synthesize them into EDIF, ready for the FPGA vendor's place and route tools.
   If you have not already nominated a top level entity/configuration in the Synthesis tab of the Options for Core Project dialog (Project » Project Options), the Choose Top-level dialog will appear. Enter the core project name or select from the dropdown list. Click OK to continue.
   
   All configurations will be synthesized and the resulting intermediary VHDL files for the schematic, EDIF files for the schematic wiring and individual parts and a synthesis logfile will be generated and display under the Generated (config_name) folders in the Projects panel.
   If there are any error messages displayed in the Messages panel, go back to the schematic to fix any issues and resynthesize.

Publishing the Core

Now we can 'publish' the core project. This will zip together (archive) all the EDIF files in the core project's Project Outputs folder, and then copy this to the user EDIF models folder that you specified earlier.

1. Select Design » Publish. If the error message 'cannot find " " working folder' appears, make sure you have set up the Use presynthesized model folder option in the FPGA - Synthesis page of the Preferences dialog.
2. Check the Messages panel (View » Workspace Panels » System » Messages) if you wish to see that the publication has successfully taken place.
3. Save the core project file.

Creating the Core Component from the Schematic

Now that the core itself is ready (in the form of a set of EDIF models), the next step is to create a schematic symbol that represents the core component, and link it to the EDIF files generated during synthesis and archived together by publishing.

1. Select Design » Generate Symbol. For this example, we will create a new library, so confirm its creation by clicking Yes in the Confirm dialog. The Symbol Options dialog appears. Select Relative Schematic Port Layout to arrange the pins on the symbol in the same arrangement as the ports on the top-level schematic in the core project. Leave the other defaults selected and click OK.
   
2. A new schematic library file (Schlib1.SchLib) opens and displays the generated symbol from the schematic called KeyPadScanner, using the ports from the schematic to create and name the pins, as shown in Figure 2 below. Save the new library as MyCores.SchLib.
   
   Figure 2. KeyPadScanner component in the Schematic Library Editor

1. Click on the SCH Library panel (View » Workspace Panels » SCH » SCH Library) to display the component's details.
2. Double-click on the component name in the SCH Library panel (or click on Edit) to display the Library Component Properties dialog.
   
   Note that the parameters have been added that indicate which child models are required to be retrieved from the published EDIF zip files.
3. You can also edit the component's pins from this dialog by clicking on the Edit Pins button to display the Component Pin Editor dialog, or double-click on a Pin name in the Pins section of the SCH Library panel to display the Pin Properties dialog. Rearrange the pins as required and save the component.
4. Save the schematic library and close.

Using the Core Component

The core component can now be used in a schematic. Make sure you remove the appropriate schematic file from the project if you are using the core component to replace an existing section of an FPGA design.
As mentioned earlier, when you synthesize a design that uses the new core component, the system will search the user EDIF folders for the required EDIF models. The location of the user EDIF models is specified in the FPGA - Synthesis page of the Preferences dialog. The search sequence for EDIF modelsis:
$project_dir
$user_edif\$vendor\$family
$user_edif\$vendor
$user_edif
$system_edif\$vendor\$family
$system_edif\$vendor
$system_edif.
Note that the search locations include the project directory, useful if you need to transfer the design to another PC that does not have the user EDIF models location defined.

Linking to the Core Project during Development

If you are still developing the core while using it in an FPGA project, you can link from the core component symbol to the core project. If this is done, when you synthesize the FPGA project, the system will search in the Project Outputs folder of the core project for the required EDIF models, rather that retrieving it from the user EDIF folders. Note that linking between a component and the core project is done by name as well, so the component has to be named the same as the project.
To link from the component symbol in the FPGA project to the core project that you used to create the component:

1. Go to the Projects panel and click on Structure Editor button to display the project structure view. Make sure that your project is compiled (Project » Compile Core Project) so that it appears in the structure tree. You will see the Valid Sub Projects and Configurations list in the bottom section of the Projects panel.
   
2. Select the software project that we just created, KeyPadScanner.PrjCor, from the Valid Sub-Projects list by clicking on its icon and drag-and-drop it onto the icon of the processor component KeyPadScanner in the top section of the panel. Note that valid targets will be highlighted. The link will be established and the structure will recompile to re-establish the integrity.