Documentation for “Zerocat PS/2-Keyboard”
Generated on: Sat, 18 Jun 2022 13:33:21 +0200
Repository: git://zerocat.org/zerocat/projects/ps2-keyboard
Version: v0.0.0-1-97c1fb5
Branch: master

Zerocat PS/2-Keyboard
– Get rid of keyloggers.

Copyright (C) 2017, 2018, 2020, 2021, 2022 Kai Mertens kmx@posteo.net

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

Section #../doc/NEWS.md

NEWS

Version Tags

Within this project’s git repository, versions are tagged according to the following pattern:

    v<major>.<minor>.<revision>

vx.x.x

v0.0.0

Section #../doc/README.md

README

Project Goal

The goal of Zerocat PS/2-Keyboard is to provide you with a save keyboard, driven by a free-design microcontroller board.

Paths

All paths within this document are relative in respect to the original location of this source file, which is located in the project’s doc/ folder.

Prerequisites

It is assumed that you are running a GNU/Linux-libre operating system.

Use git to clone the project’s sources:

    git clone git://zerocat.org/zerocat/projects/ps2-keyboard

Change into the project’s documentation folder:

    cd ps2-keyboard/doc/

Study this README.md to get started:

    cat ../doc/README.md

GNU Guix System

If you are on GNU Guix System, use make to create a dedicated profile, once. This allows you to match your environment to the one used by Zerocat, thus producing bit-identical results:

    make -C ../guix pull

Create an empty environment with dedicated guix channel:

    make -C ../guix environment

Create a shell with all prerequisites set up:

    make -C ../guix shell

To leave the shell and the environment, later on, when you are done with this project, type:

    exit
    exit

To remove this project’s handy guix profile, type:

    make -C ../guix clean

This will remove symlinks only. If you want to remove the profile from your system, run the GNU Guix Garbage Collector.

To list all available targets, type:

    make -C ../guix help

Other Distro

If you are on another distro, check file ../guix/manifest.scm and install the listed packages with your package manager, manually. Adapt package names as required.

Make Documentation

To build the documentation, type:

    make -C ../doc

To get a full list of available targets, type:

    make -C ../doc help

To clean-up, type:

    make -C ../doc clean

Make Firmware

To build the firmware, type:

    make -C ../firmware/src

To get a full list of available targets, type:

    make -C ../firmware/src help

To clean-up, type:

    make -C ../firmware/src clean
Section #../doc/COPYING.md

Copying

Zerocat PS/2-Keyboard ships copyrighted work.

Zerocat PS/2-Keyboard is free software. It makes use of free software approved licenses only and should be freely distributable:

Authorship, copyright and license information may be provided in more detail on a per-folder and/or per-file basis. Check the sources.

Please report a bug if you find the distribution hindered.
See Zerocat Website for contact information.

Section #../doc/CONTRIBUTING.md

Contributing

Documentation Files

Documentation source files are written in markdown syntax. They should carry their individual copyright and license notices right below the title giving headline, e.g.:

    <Title-of-Document>
    ===================

    Copyright (C) <Year>  <Name-of-Author> <Email-Address>  

    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.3
    or any later version published by the Free Software Foundation;
    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
    Texts. A copy of the license is included in the section entitled
    "GNU Free Documentation License".

    <Other-Headline>
    ----------------

    ...content...

The generated documentation carries a license notice right at top on its title page, with copyright statements generated from git log output.

Sections of the generated documentation are build from selected markdown source files, with their individual copyright and license notice stripped.

In order to enrich the generated documentation ...

... and adapt ../doc/Makefile to produce nice output.

In case more tools are needed, don't forget to update ../guix/manifest.scm.

Images

To make your image look nice within the documentation, select a landscape layout of 16:9 aspect ratio.

Use ImageMagick to prepare your image, e.g.:

If your image is big, reduce it to a maximal width of 2000 pixel:

    mogrify -resize 2000x <image>

Please clean image files from metadata, before committing, i.e.:

    mogrify -strip <image>

If you embed your image into a markdown documentation file, use this syntax:

   ![<path/to/image>][]

   [<path/to/image>]:     <path/to/image>     "title message"

or alternatly:

   ![<path/to/image>][my-image-shortcut]

   [my-image-shortcut]:   <path/to/image>     "title message"

These patterns will guarantee that <img> tags will have their src, alt and title attributes properly set within the html output.

Code Files

Please use this license header for code source files:

    Zerocat PS/2-Keyboard --- Get rid of keyloggers.

    Copyright (C) <Year>  <Name-of-Author> <Email-Address>

    This file is part of Zerocat PS/2-Keyboard.

    Zerocat PS/2-Keyboard is free software: you can redistribute it
    and/or modify it under the terms of the GNU General Public
    License as published by the Free Software Foundation, either
    version 3 of the License, or (at your option) any later
    version.

    Zerocat PS/2-Keyboard is distributed in the hope that it will be
    useful, but WITHOUT ANY WARRANTY; without even the implied
    warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
    PURPOSE. See the GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Zerocat PS/2-Keyboard.
    If not, see <http://www.gnu.org/licenses/>.

Shell Scripts

If you intend to write shell scripts, use this skeleton to make them work for GNU Guix:

    #!/bin/sh

    # Re-exec if we are not using Bash or are using Bash in POSIX mode.
    if [ -z "$BASH" ] || [ "$BASH" = "/bin/sh" ]; then
      bash=`command -v bash`
      if [ -z "$bash" ]; then
        echo "Couldn't find Bash, sorry!"
        exit 1
      else
        exec "$bash" "$0" "$@"
      fi
    fi

    # We're using Bash now.
    set -o errexit
    set -o nounset
    set -o pipefail

    # Your code goes here ...

ChangeLog

Update ../doc/NEWS.md and list your contributions.

You can use git shortlog to get a starting point for your edit.

Section #../doc/ps2.md

PS/2

WWW Articles

Advantages

Short List of Specs

PS/2 Pinout Cross Reference

    Function          | 6-pin DIN (PS/2) | 5-pin DIN (AT/XT)  | 6-pin SDL
    --------          | ---------------- | -----------------  | ---------
    +5V               | 4                | 5                  | E
    DATA              | 1                | 2                  | B
    not connected     | 2, 6             | 3                  | A, F
    GND               | 3                | 4                  | C
    CLK               | 5                | 1                  | D

Pinout 6-Pin DIN

    >
    > Socket:                       Plug:
    >             6   _   5                    5   _   6
    >              o | | o                      · | | ·
    >                |_|                          |_|
    >             o       o                    ·       ·
    >            4         3                  3         4
    >               o   o                        ·   ·
    >              2     1                      1     2
    >

Pinout 5-Pin DIN

    >
    > Socket:                       Plug:
    >              _   _                         _   _
    >               \_/                           \_/
    >
    >           3         1                   1         3
    >          o           o                 ·           ·
    >             5     4                       4     5
    >            o   2   o                     ·   2   ·
    >                o                             ·
    >

Pinout 6-Pin SDL

    >
    > Socket:                       Plug:
    >
    >
    >         xxxxxxxxxxxxxxx               xxxxxxxxxxxxxxx
    >           | | | | | |                   | | | | | |
    >           F E D B C A                   A B C D E F
    >
    >

PS/2 Combi Ports

Mainboards and ThinkPad docking stations often carry a so called PS/2 Combi Port, with keyboard and mouse icons at the outlet. The exact wiring is unknown to the author, three options should be taken into account. Each option would require different usage of a dedicated Y-Splitter-Cable.

  1. Combi Port is a PS/2-Keyboard Port with extra clock and data lines for mouse at pins 6 and 2.

  2. Combi Port is a PS/2-Mouse Port with extra clock and data lines for keyboard at pins 6 and 2.

  3. Combi Port is a standard PS/2 port (pins 6 and 2 not connected) which is able to detect the type of device at boot time. Using both devices (keyboard and mouse) simultaneously is not supported.

Port types 1.) and 2.) would require to use a Y-Splitter-Cable (see Figure A) for simultaneous operation of keyboard and mouse. Port type 2.) would additionally require to twist the plugs, thus using the mouse with the keyboard plug and vice-versa.

    >
    >     Figure A: PS/2 Y-Splitter-Cable
    >     ===============================
    >
    >   6-pin Mini-DIN            6-pin Mini-DIN               6-pin Mini-DIN
    >  (PS/2 Combi Port)          (PS/2-Keyboard)              (PS/2-Mouse)
    >
    >         1 -------------------------- 1
    >         2 --------------------------------------------------------1
    >         3 -------------------------- 3 -------------------------- 3
    >         4 -------------------------- 4 -------------------------- 4
    >         5 -------------------------- 5
    >         6 --------------------------------------------------------5
    >
    >

PS/2-Keyboard Port with Dual Keyboard-Like Devices

Note the different layout of a Y-Splitter-Cable which allows for simultaneous usage of keyboard-like devices:

    >
    >     Figure B: PS/2 Y-Splitter-Cable
    >     ===============================
    >
    >    6-pin Mini-DIN            6-pin Mini-DIN               6-pin Mini-DIN
    >  (PS/2 Keyboard Port)       (PS/2 Keyboard)           (PS/2 Barcode Scanner)
    >
    >         1 -------------------------- 1 -------------------------- 1
    >         3 -------------------------- 3 -------------------------- 3
    >         4 -------------------------- 4 -------------------------- 4
    >         5 -------------------------- 5 -------------------------- 5
    >
    >

PS/2 Hardware Support with Coreboot

Coreboot seems to not support PS/2 hardware in first place. Documentation about PS/2 is often lacking details on coreboot’s board status pages. i.e.:

Exact lists about which hardware works how has to be gathered individually and would be a required source of information.

Section #../doc/controller-board.md

The Controller Board

List of Files

Test Setup 1

Test Setup 2

    +-----------------------+
    |                       |                 +----------------------+
    |   Laptop ZC-T60       |                 |                      |
    |   + Docking           |<-- USB Power -->|  Zerocat             |
    |     + RS232 Port?     |<---- RS232 ---->|  PS/2 Controller     |
    |     + PS/2 Port       |<---- PS/2 ----->|  Board               |
    |                       |                 |                      |
    |                       |                 +----------------------+
    +-----------------------+
            ^
            |
            |
        +-----------+
        |           |
        | 230VAC    |
        | Power     |
        |           |
        +-----------+

Circuit Preview

Nothing evolved, so far. Let’s start with this basic board:

PS/2 Controller Board

Board Schematic PNG Preview

Section #../doc/points-of-interest.md

Points of Interest

Websites

Section #../doc/x200-keyboard-hack.md

X200 Keyboard Hack

Keyboard Disassembled

ThinkPad X200 Keyboard Disassembled (Mechanics of one Key Missing)

ThinkPad X200 Keyboard Disassembled (Mechanics of one Key Missing)

Listed Overview

Double Layer Keyboard Cable

Keyboard Cable, splits towards Systemboard and Trackpoint

Keyboard Cable, splits towards Systemboard and Trackpoint

Systemboard Connector from JAE, 40-pin + 4 Hold Downs (CONN40A-1-U1GP)

Systemboard Connector, unknown Type

Circuit Schematic

Schematic of an X200 Keyboard Cable with 32-pin PTPM754DR TrackPoint Controller

Schematic of an X200 Keyboard Cable with 32-pin PTPM754DR TrackPoint Controller

Keyboard I/O Pads

As visible from the x200 keyboard cable schematics, the keyboard foil pads are organized in...

...resulting in 36 active pads.

Double Layer with integrated Vias

Double Layer with integrated Vias

Keyboard Connector Pads, Top and Bottom

Keyboard Connector Pads, Top and Bottom

Trackpoint Board

Please read PS/2 to get prepared for PS/2 basics.

Pad Connection

The trackpoint board is connected to the keyboard cable by eight soldered pads, referenced by names Pad-1..Pad-8 within this documentation. Pad-1 is located close to the board’s edge.

    Pad Number  | Function        | Remarks                                                 | 9-pin Sub-D Test Plug
    ----------  | --------        | -------                                                 | ---------------------
    1           | CLK             | close to board’s edge                                   | 9
    2           | RST             | can be connected to positive POR, alternatively         | 4
    3           | MIDDLE BUTTON   | -                                                       | 8
    4           | RIGHT BUTTON    | -                                                       | 3
    5           | LEFT BUTTON     | -                                                       | 7
    6           | DATA            | -                                                       | 2
    7           | VSS (GND)       | connected to thicker route in keyboard cable            | 6
    8           | VCC (+5V)       | connected to thicker, edgemost route of keyboard cable  | 1
    -           | -               | -                                                       | 5

Alternative Power-On-Reset (POR)

    >
    >   Alternative POR at RST (Pad 2)
    >   ==============================
    >
    >              C
    >   VCC --------||------+
    >              2.2µF    |
    >                       |     R
    >   RST ----------------+------/\/\/------- GND
    >                               100K
    >

Modified Cable

The Keyboard Cable has been modified to ease experimenting with the disassembled Trackpoint Board. Test Connector is a SUB-D9 male plug.

Modified Keyboard Cable to Ease Experimenting

Modified Keyboard Cable to Ease Experimenting

Onboard Controller

Controller in use is the TPM754 from Philips Semiconductors. This is a 8051-based machine which runs proprietary code from IBM:

“IBM has licensed Philips Semiconductors to sell microcontrollers with TrackPoint code. By purchasing a TPM from Philips, the purchaser becomes a sub-licensee of Philips. The selling price of Philips’ TPM includes the royalties for IBM’s intellectual property, which Philips in turn pays to IBM. Customers for TPMs do not need to sign any licensing agreement with either IBM or Philips. This code is the intellectual property of IBM, which is covered by numerous patents, and must be treated accordingly.” --- Philips Semiconductors TPM754 Datasheet

The TPM754 comes in different packages with different ordering codes. Unfortunately there is no datasheet nor pinout available for the 32-pin SSOP package (ordering code PTPM754DR), but in regard to measurements and the 28-pin SSOP datasheet, the pinout can be guessed in a straight foreward approach.

PTPM754DR 32-pin SSOP Pinout

    Pin   | Function        | Connected Board Pad           | External PS/2 Mouse (6-pin Mini-DIN)
    ---   | --------        | -------------------           | ------------------------------------
    1     | RxD/T0/P3.4     | -                             | Pin 1 (DATA)
    2     | TxD/T1/P3.5     | Pad 1 (CLK), close to edge    | -
    3     | ECI/P3.6        | -                             | -
    4     | INT1/P3.7       | -                             | Pin 5 (CLK)
    5     | RST             | Pad 2 (RST)                   | -
    6     | X2              | -                             | -
    7     | X1              | -                             | -
    8     | VSS             | Pad 7 (GND)                   | Pin 3 (GND)
    9     | ZIN             | -                             | -
    10    | YIN             | -                             | -
    11    | XIN             | -                             | -
    12    | XYZRAMP         | -                             | -
    13    | AVSS            | -                             | -
    14    | AVCC            | -                             | -
    15    | not connected   | -                             | -
    16    | not connected   | -                             | -
    17    | VCC? AVCC?      | -                             | -
    18    | not connected   | -                             | -
    19    | DECOUPLE        | -                             | -
    20    | VREG            | -                             | -
    21    | XYDACBIAS       | -                             | -
    22    | XYSOURCE        | -                             | -
    23    | ZDAC/ASEL       | -                             | -
    24    | XYDAC           | -                             | -
    25    | P1.2            | -                             | -
    26    | VCC             | Pad 8 (VCC)                   | Pin 4 (VCC)
    27    | CEX/P1.1        | -                             | -
    28    | INT0/P1.0       | Pad 6 (DATA)                  | -
    29    | P3.0            | Pad 5 (LEFT BUTTON)           | -
    30    | P3.1            | Pad 4 (RIGHT BUTTON)          | -
    31    | P3.2            | Pad 3 (MIDDLE BUTTON)         | -
    32    | P3.3            | -                             | -

PS/2-Mouse at H8’s TrackPoint Interface

Warning: If the TrackPoint is replaced by a PS/2-Mouse, interfacing with the sysboard’s H8 controller doesn't work. Probably, H8 and TrackPoint Controller do not talk according to PS/2 standards??

PS/2-Mouse via Trackpoint Board

Although no interface is provided to attach an additional external PS/2 Mouse, pins 1 and 4 of the TPM754 can be used as a workaround in conjunction with the VCC and GND power lines. The IBM code separates data streams from Trackpoint and Mouse clearly, so that one device moves the screen pointer without being irritated by the other.

Experimental Setup with External PS/2 Mouse

Experimental Setup with External PS/2 Mouse

Connecting the Trackpoint Board

Connecting the Trackpoint Board

TrackPoint at PS/2 Mouse Port

    >
    >     Connect Trackpoint via Test Plug to a Standard PS/2 Mouse Port
    >     ==============================================================
    >
    >
    >     +---------VCC---------------------+--------> to Pin 4
    >     | +----------------DATA-----------|--------> to Pin 1
    >     | |                               |
    >     | |   +------RST-------+---||-----+
    >     | |   |                |   2.2uF
    >    1|2|3 4|5               |
    >   \ · · · · · /            +--/\/\/---+
    >    \ · · · · /                 100K   |
    >     6|7 8 9|                          |
    >      |     |                          |
    >      |     +-----------CLOCK----------|--------> to Pin 5
    >      +---------GND--------------------+--------> to Pin 3
    >
    >   Sub-D9 Test Plug      ---->    PS/2 6-pin Mini-DIN
    >
    >

This setup has been proved to work with a D945GCLF Intel Desktop Board, running blobless coreboot firmware and the Trisquel7 Operating System. The Trackpoint and its attached external PS/2-Mouse is recognized at the PS/2 Mouse Port along with a PS/2-Keyboard (IBM Model M) attached to the PS/2 Keyboard Port. The reset line of the Trackpoint is simulated by the alternative Power-On-Reset circuit.

Trackpoint with External PS/2-Mouse at Standard PS/2 Mouse Port of a Blobless Coreboot Machine

Trackpoint with External PS/2-Mouse at Standard PS/2 Mouse Port of a Blobless Coreboot Machine

Drafted Idea for a PS/2-Keyboard with Trackpoint and External Mouse

    >
    >   PS/2-Keyboard Setup using an X200 Keyboard Matrix with Trackpoint and external Mouse
    >   ====================================================================================
    >
    >
    >  ····························································································
    >  :                                                                                          :
    >  :                                                  +-----------------------------------+   :
    >  :  +-----------------------+                       | Board with Free-Design Controller |   :
    >  :  | X200 Keyboard         |-----GND---/4----------| ================================= |   :
    >  :  | =============         |                       |                                   |   :
    >  :  |                       |=====PB and Hotkey=========discard or translate====+       |   :
    >  :  | No controller in use. |                       |___                        |       |   :
    >  :  |                       |-----KBDID0----------->|   |                       |       |   :
    >  :  | * Power Button (PB)   |-----KBDID1----------->| ? |                       |       |   :
    >  :  | * Fn Hotkey           |-----KBDID2----------->|___|                       |       |   :
    >  :  | * Matrix 16x8         |                       |                           |       |   :
    >  :  | * 3 Mouse Buttons     |-----Matrix 16x8-----------------/24----------+    |       |   :
    >  :  | * KBDID0..2 Lines     |                       |                      |    |       |   :
    >  :  | * 4x Ground           |---Mouse Button M----->|                      |    /2      |   :
    >  :  | = 36 Pads             |---Mouse Button R----->|                      |    |       |   :
    >  :  |                       |---Mouse Button L----->|                      |    |       |   :
    >  :  +-----------------------+                       |                      v    v       |   :
    >  :                                                  |              +················+   |   :
    >  :                                                  |              : translate into :   |   :
    >  :  +-----------------------+                       |              :      PS/2      :   |   :
    >  :  | TrackPoint Board      |<<====+5V, GND===============\\       +················+   |   :
    >  :  | ================      |                       |     ||               ^            |   :
    >  :  |                       |<---Mouse Button M-----|   __||___________    |            |   :
    >  :  | 8051-based controller |<---Mouse Button R-----|  |  +5V, GND     |   |            |   :
    >  :  | (PTPM754DR) runs      |<---Mouse Button L-----|  |_______________|   |            |   :
    >  :  | proprietary code      |                       |    |     ^     ^     |            |   :
    >  :  | from IBM.             |<-------Reset----------|    |     |     |     |            |   :
    >  :  |                       |                       |    /2    /2    /2    /2           |   :
    >  :  | * 3x Mouse Buttons    |     PS/2-Trackpoint   |    |     |     |     |            |   :
    >  :  | * PS/2 (clock, data)  |<=======clock/data================+     |     |            |   :
    >  :  | * Reset Line          |       PS/2-Mouse      |    |     |     |     |            |   :
    >  :  | * Ground              |                       |    |     |     +-----|            |   :
    >  :  | * +5V Power           |    Ext. PS/2 Mouse    |    v     |           |            |   :
    >  :  | * Ext. PS/2           |<======clock/data===========+     |           |            |   :
    >  :  | = 10 Lines            |                       |    |     |           |            |   :
    >  :  |                       |                       |    |     |           |            |   :
    >  :  +-----------------------+                       +----|-----|-----------|------------+   :
    >  :                                                       |     |           |                :
    >  :  PS/2-Keyboard with Trackpoint                        /4    /4          /4               :
    >  ························································|·····|···········|·················
    >                                                          |     |           |
    >                 +--------Ext. PS/2-Mouse-----------------+     |           |
    >                 |                                              |           |
    >                 |                                              v           v
    >                 |                     +-----------------------------------------------------+
    >                 v                     |                   :| PS/2  |   | PS/2     |:        |
    >   +------------------------+          |                   :| Mouse |   | Keyboard |:        |
    >   | External PS/2 Mouse    |          |                   :|_______|   |__________|:        |
    >   | ===================    |          |                   ·····PS/2-Combi-Port?·····        |
    >   |                        |          |                                                     |
    >   | proprietary controller |          | Blobfree Coreboot Computer or Laptop                |
    >   |                        |          | ====================================                |
    >   | * PS/2                 |          |                                                     |
    >   | = 4 Lines              |          | * with two PS/2 Ports                               |
    >   |                        |          | * or with one PS/2 Combi Port and Y-Splitter-Cable  |
    >   +------------------------+          |                                                     |
    >                                       | Working Example(s):                                 |
    >                                       |                                                     |
    >                                       | * D945GCLF Desktop Board with Blobless Coreboot     |
    >                                       |                                                     |

Conclusion

In case a desktop board with blobless coreboot is used as host, this PS/2 free-design keyboard would significantly improve the computer user’s situation in respect to freedom and security. Let’s go for prototyping!

Section #../doc/GNU-FDL.md

GNU Free Documentation License

Version 1.3, 3 November 2008

Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. http://fsf.org/

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

The "publisher" means any person or entity that distributes copies of the Document to the public.

A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

11. RELICENSING

"Massive Multiauthor Collaboration Site" (or "MMC Site") means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A "Massive Multiauthor Collaboration" (or "MMC") contained in the site means any set of copyrightable works thus published on the MMC site.

"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

"Incorporate" means to publish or republish a Document, in whole or in part, as part of another Document.

An MMC is "eligible for relicensing" if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

    Copyright (C)  YEAR  YOUR NAME.
    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.3
    or any later version published by the Free Software Foundation;
    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
    A copy of the license is included in the section entitled "GNU
    Free Documentation License".

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with … Texts." line with this:

    with the Invariant Sections being LIST THEIR TITLES, with the
    Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.