+ Initial implementation

docs/ports.tex

@@ -0,0 +1,81 @@
+%
+%   $Id$
+%   This file is part of the FPC documentation.
+%   Copyright (C) 1997, by Michael Van Canneyt
+%
+%   The FPC documentation is free text; you can redistribute it and/or
+%   modify it under the terms of the GNU Library General Public License as
+%   published by the Free Software Foundation; either version 2 of the
+%   License, or (at your option) any later version.
+%
+%   The FPC Documentation 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
+%   Library General Public License for more details.
+%
+%   You should have received a copy of the GNU Library General Public
+%   License along with the FPC documentation; see the file COPYING.LIB.  If not,
+%   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+%   Boston, MA 02111-1307, USA.
+%
+\chapter{The PORTS unit}
+
+\section{Introduction}
+The ports unit implements the \var{port} constructs found in \tp. 
+It uses classes and default array properties to do this.
+
+The unit exists on \linux, \ostwo and \dos. It is implemented only for
+compatibility with \tp. It's usage is discouraged, because using ports
+is not portable programming, and the operating system may not even allow
+it (for instance \windows).
+
+Under \linux, your program must be run as root, or the \var{IOPerm} call
+must be set in order to set appropriate permissions on the port access.
+
+\section{Types,constants and variables}
+
+\subsection{Types}
+The following types are defined to implement the port access.
+\begin{verbatim}
+tport = class
+  protected
+    procedure writeport(p : longint;data : byte);
+    function  readport(p : longint) : byte;
+  public
+    property pp[w : longint] : byte read readport write writeport;default;
+end;
+
+tportw = class
+  protected
+    procedure writeport(p : longint;data : word);
+    function  readport(p : longint) : word;
+  public
+    property pp[w : longint] : word read readport write writeport;default;
+end;
+
+tportl = class
+  Protected
+    procedure writeport(p : longint;data : longint);
+    function  readport(p : longint) : longint;
+  Public
+   property pp[w : Longint] : longint read readport write writeport;default;
+end;
+\end{verbatim}
+Each of these types allows access to the ports using respectively, a byte, a
+word or a longint sized argument.
+
+Since there is a default property for each of this types, a sentence as
+\begin{verbatim}
+  port[221]:=12;
+\end{verbatim}
+Will result in the byte 12 being written to port 221, if port is defined
+as a variable of type \var{tport}
+\subsection{variables}       
+The following variables are defined:
+\begin{verbatim}
+port,
+portb : tport;
+portw : tportw;
+portl : tportl;
+\end{verbatim}
+They allow access to the ports in a \tp compatible way.