/*
    ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio.

    This file is part of ChibiOS/RT.

    ChibiOS/RT 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.

    ChibiOS/RT 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 this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/**
 * @page article_design Designing an embedded application
 * ChibiOS/RT offers a variety of mechanisms and primitives, often it is
 * better to focus on a single approach for the system design and use only
 * part of the available subsystems.<br>
 * When designing your application you may choose among several design
 * alternatives:
 * - @ref nothreads
 * - @ref messpass
 * - @ref thdshared
 * - @ref thdmixed
 * .
 * @section nothreads Single threaded superloop
 * Correct, single thread, it is not mandatory to use the multithreading
 * features of the OS. You may choose to implements everything as a complex
 * state machine handled in the main thread alone. In this scenario the OS
 * still offers a variety of useful mechanisms:
 * - Interrupt handling.
 * - Virtual Timers, very useful in state machines in order to handle time
 *   triggered state transitions.
 * - Power management.
 * - Event Flags and/or Semaphores as communication mechanism between
 *   interrupt handlers and the main.
 * - I/O queues.
 * - Memory allocation.
 * - System time.
 * .
 * In this configuration the kernel size is really minimal, everything else
 * is disabled and takes no space. You always have the option to use more
 * threads at a later time in order to perform separate tasks.
 *
 * @section messpass Message Passing
 * In this scenario there are multiple threads in the system that never
 * share data, everything is done by exchanging messages. Each thread
 * represents a service, the other threads can request the service by sending
 * a message.<br>
 * In this scenario the following subsystems can be used:
 * - Synchronous Messages.
 * - Mailboxes (asynchronous message queues).
 * .
 * The advantage of this approach is to not have to deal with mutual exclusion,
 * each functionality is encapsulated into a server thread that sequentially
 * serves all the requests. As example, you can have the following scenario:
 * - A buffers allocator server.
 * - A disk driver server.
 * - A file system server.
 * - One or more client threads.
 * .
 * Example:
 * <br><br>
 * @dot
  digraph example {
      rankdir="RL";
      node [shape=rectangle, fontname=Helvetica, fontsize=8, fixedsize="true",
            width="1.2", height="0.75"];
      edge [fontname=Helvetica, fontsize=8];
      disk [label="Server Thread\nDisk Driver"];
      buf [label="Server Thread\nBuffers Allocator"];
      fs [label="Client&Server Thread\nFile System"];
      cl1 [label="Client Thread"];
      cl2 [label="Client Thread"];
      cl3 [label="Client Thread"];
      fs -> disk [label="I/O request", constraint=false];
      disk -> fs [label="status", style="dotted", constraint=false];
      fs -> buf [label="buffer request"];
      buf -> fs [label="buffer", style="dotted"];
      cl1 -> fs [label="FS transaction"];
      fs -> cl1 [label="result", style="dotted"];
      cl2 -> fs [label="FS transaction"];
      fs -> cl2 [label="result", style="dotted"];
      cl3 -> fs [label="FS transaction"];
      fs -> cl3 [label="result", style="dotted"];
  }
 * @enddot
 * <br><br>
 * Note that the threads should not exchange complex messages but just
 * pointers to data structures in order to optimize the performance.
 * Also note that a thread can be both client and server at the same
 * time, the FS service in the previous scenario as example.
 *
 * @section thdshared Threads sharing data
 * This is the most common scenario, several threads have access to both their
 * private data and shared data. Synchronization happens with one of the
 * mechanisms described in the @ref article_mutual_exclusion article.<br>
 *
 * @section thdmixed Mixed
 * All the above approaches can be freely mixed in a single application but
 * usually I prefer to choose a way and consistently design the system around
 * it. The OS is a toolbox that offers a lot of tools but you don't have
 * to use them all necessarily.
 */