======================================== XESS VHDL Library Files

These are VHDL files for modules that are useful in a variety of larger designs for XESS FPGA boards (and possibly others).

Library Organization

The main part of this library is in the top-level directory, and it is pretty simple: it's just a bunch of VHDL files containing modules that perform certain functions, hopefully functions you actually want. Some of the modules reference others. For example, many of the modules reference the CommonPckg package in the common.vhd file.

In the Board_Packages subdirectory below the top-level are some very important VHDL files which are not actually part of the library. Each of these files contains a package of constants and definitions for a particular XESS FPGA board. By adding one of these files to your project, you customize this library for that FPGA board.

The Board_Packages subdirectory also has constraint files (with a .ucf suffix) containing the FPGA pin assignments for each XESS FPGA board.

How to Use This Library

#. Place these files in a directory somewhere.

#. Start a Xilinx ISE project.

#. Select the Project => New VHDL Library... menu item. In the New VHDL Library window, enter XESS as the name of the library. Then enter the directory where these VHDL files are stored as the library location. Finally, click OK.

#. Select the Project => Add Source... menu item. In the Add Source window, go to the Board_Packages subdirectory in the library directory and select the file associated with the XESS board you are designing for. Then click on the Open button. (Add Source... is used here so you'll always access the most current board configuration in case there are corrections or additions.)

#. Select the Project => Add Copy of Source... menu item. In the Add Copy of Source window, go to the Board_Packages subdirectory in the library directory and select the UCF file associated with the XESS board you are designing for. Then click on the Open button. (Add Copy of Source... is used here so you'll have a local copy of pin assignments that you can edit to give them names appropriate for your particular project without affecting the pin assignments in other projects.)

#. Create the rest of the VHDL files for your design. To access the elements of this library, place code like this into your files::

    library XESS;
    use XESS.CommonPckg.all;
    use XESS.PwmPckg.all;
    ...

(You can find the available packages by looking inside each of the VHDL files.)

Do this if you want to access any of the constants found in the board package file::

    use work.XessBoardPckg.all;

(Since you used Project => Add Source... to add the board definition file to your project, then it is automatically included in the default work library.)

How to Fix a Project with Missing Files

After you've downloaded an XESS design project, you may get errors with missing files when you try to open or compile it. That's probably because this library isn't in the place where the project expects to find it. You could move this library to the place the project wants it, but it's probably better to just modify the project as follows:

#. In the Libraries tab of the ISE Navigator window, right-click on the XESS library entry and select Remove from the pop-up menu.

#. In the Files tab of the ISE Navigator window, right-click on any files that are in the VHDL_Lib\Board_Packages subdirectory and select Remove from the pop-up menu.

Once these items are removed, you can add them back using the procedure described in the previous section. Then the missing file errors should be gone.

Library Contents

Audio:
    An interface to an AK4565 audio codec for sampling and generating
    20-bit stereo signals.
    
ButtonDebounver.vhd:
    A debouncing circuit for a pushbutton.
    
ButtonScanner.vhd:
    An interface for scanning the button array on the StickIt! Buttons module.

ClkGen.vhd:
    A clock generator module that uses a DCM to multiply or divide an input clock to create an
    output clock with a higher or lower frequency. Also includes a simpler module that divides
    a master clock to generate lower frequencies.

Common.vhd:
    Contains useful constants and functions.
    
Delay.vhd:
    Modules to delay signals or buses by one or more clock cycles.
    
Fifo.vhd:
    Simple FIFO modules in common-clock and independent-clock versions.

FlashCntl.vhd:
    A module that provides read/write access to the serial flash device on the XuLA board.
    
Hcsr04.vhd:
    An interface to an HCSR04 ultrasonic distance sensor.

HostIo.vhd:
    A set of modules that let a host PC pass data back-and-forth with
    a user design running in the FPGA.
    
HostIoComm.vhd:
    An interface that lets a PC pass data back-and-forth with a user design
    running in the FPGA via a set of download and upload FIFO buffers.
    
HostIoToI2c.vhd:
    An interface that lets the host PC pass data back-and-forth with
    a chip that has an I2C interface.
    
HostIoToSpi.vhd:
    An interface that lets the host PC pass data back-and-forth with
    a chip that has an SPI interface.
    
I2c.vhd:
    A master-to-slave I2C interface.
    
LedDigits.vhd:
    An interface to the Charlieplexed LED array on the StickIt! LED Digits module.
    
Misc.vhd:
    Miscellaneous modules that don't fit under any other category.

MemTest.vhd:
    A module that writes a random stream of values to memory.
    
PatternGen.vhd:
    A module to output a sequence of words stored in a ROM.

Pwm.vhd:
    A simple pulse-width modulator and a single-shot pulse generator.
    
RandGen.vhd:
    An LFSR-based module for generating random values.
    
RotaryEncoder.vhd:
    An interface to detect CW/CCW rotation of a rotary encoder.
    
SDCard.vhdl:
    An interface module that simplifies reading/writing to a Secure Digital Flash card.

SdramCntl.vhd:
    An interface module that makes an SDRAM appear as a simple SRAM-like memory to
    a user design in the FPGA.
    
Spi.vhd:
    A master-to-slave SPI interface.

SyncToClk.vhd:
    Modules that sync one or more signals crossing from one clock domain to another.

TestBoardCore.vhd:
    A module that tests the functioning of a XuLA board by writing a random stream of values into SDRAM
    and then reading it back and comparing it to the original.

Vga.vhd:
    Modules for generating bitmapped and character mapped displays on VGA monitors.