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README for the GCpad core

=========================

Version: $Id: README 41 2009-04-01 19:58:04Z arniml $

Description

-----------

The GCpad core interfaces to the gamepad used with the Nintendo Gamecube video

gaming system. The core communicates with the gamepad using its proprietary

communication protocol and offers the retrieved information for further

processing.

To suit the needs of the integrating system, two different flavors of the core

are available:

  * For simple applications the basic flavor manages all communication issues

    with the gamepad and provides the current status of the buttons and analog

    axes at its interface. The integrating system does not need to interfere

    with gamepad communication and can statically read the button and axes

    status information.

  * The full flavor allows full control of the gamepad communication by the

    integrating system. This flavor offers a command and response interface

    which is driven by the system to send arbitrary commands to the

    gamepad. The response of the gamepad is available for further processing.

Connecting the Pad

------------------

Information is exchanged between the gamepad and the host side over a single

wire. Both sides seem to implement an open-collector style output

driver. Therefore, an external pull-up resistor of 1kOhm to the 3.43V supply

is required at the DATA line.

Sticking exactly to the 3.3V supply seems not to be necessary. I use the 3.3V

supply which is available from the FPGA board. Please note that the 5V supply

is required for certain controller types even if the rumble motor is not used.

The connector seems to be a special type designed for the Gamecube. It might

be hard to find a matching counterpart. If you do not want to rip up the

controller cable then your alternative option might be to reuse an extension

cable. They are quite cheap and pass through all required wires. Just remove

the connector that is plugged into the console and attach your favorite

standard connector.

See gcpad.png.

Verification

------------

The GCpad core comes with a simple testbench that includes a simulation model

of a Gamecube controller. Serial information is sent to the core and the

reported button states are compared against the input. Both flavors are tested

in parallel there.

You should normally not need to run the testbench. But in case you modified

the VHDL code the testbench gives some hints if the design has been broken.

Directory Structure

-------------------

The core's directory structure follows the proposal of OpenCores.org.

gcpad

 |

 \--+-- doc                 : Integration Manual

    |

    +-- rtl

    |    |

    |    \-- vhdl           : VHDL code containing the RTL description

    |                         of the core.

    |

    +-- bench

    |    |

    |    \-- vhdl           : VHDL testbench code.

    |

    \-- sim

         |

         \-- rtl_sim        : Directory for running simulations.

Compiling the VHDL Code

-----------------------

VHDL compilation and simulation tasks take place inside in sim/rtl_sim

directory. The project setup supports only the GHDL simulator (see

http://ghdl.free.fr).

To compile the code simply type at the shell

$ make

This should result in a file called tb_behav_c0 which can be executed as any

other executable.

The basic simple sequence list can be found in COMPILE_LIST. This can be

useful to quickly set up the analyze stage of any compiler or

synthesizer. Especially when synthesizing the code, you want to skip the VHDL

configurations in *-c.vhd and everything below the bench/ directory.

References

----------

  * James' excellent page covering many details of the Gamecube controller

    protocol

    http://www.int03.co.uk/crema/hardware/gamecube/gc-control.htm

  * Yet Another Gamecube Documentation

    http://www.gc-linux.org/docs/yagcd/index.html

    Refer to section 5.8, 9.1 and 9.2.