path: root/docs/ch.txt

/**
 * @mainpage ChibiOS/RT
 * @author Giovanni Di Sirio (gdisirio@users.sourceforge.net).
 * @section Chibi Chibi ?
 * It is the Japanese word for small as in small child. So ChibiOS/RT
 * \htmlonly (<span class="t_nihongo_kanji" xml:lang="ja" lang="ja">&#12385;&#12403;</span>OS/RT) \endhtmlonly
 * means small Real Time Operating System.
 * Source <a href="http://en.wikipedia.org/wiki/Chibi" target="_blank">Wikipedia</a>.
 * @section ch_features Features
 * <ul>
 * <li>Free software, GPL3 licensed.</li>
 * <li>Designed for realtime applications.</li>
 * <li>Easily portable.</li>
 * <li>Mixed programming model:</li>
 *   <ul>
 *   <li>Synchronous, using semaphores/mutexes and/or messages.</li>
 *   <li>Asynchronous, using event sources.</li>
 *   <li>Mix of the above models, multiple threads listening to multiple event
 *       sources while serving message queues.</li>
 *   </ul>
 * <li>PC simulator target included, the development can be done on the PC
 *     using MinGW or VS.
 *     Timers, I/O channels and other HW resources are simulated in a
 *     Win32 process and the application code does not need to be aware of it.
 *     MinGW and VS demos available and ready to go, use them as templates for
 *     your application.</li>
 * <li>Unlimited number of threads.</li>
 * <li>Unlimited number of virtual timers.</li>
 * <li>Unlimited number of semaphores.</li>
 * <li>Unlimited number of mutexes.</li>
 * <li>Unlimited number of event sources.</li>
 * <li>Unlimited number of messages in queue.</li>
 * <li>Unlimited number of I/O queues.</li>
 * <li>No static setup at compile time, there is no need to configure a maximum
 *     number of all the above resources.</li>
 * <li>No *need* for a memory allocator, all the kernel structures are static
 *     and declaratively allocated. A memory allocator can be used in your
 *     application but it is not required by the ChibiOS/RT itself.</li>
 * <li>Threads, Semaphores, Event Sources, Virtual Timers creation/deletion at
 *     runtime.</li>
 * <li>Blocking and non blocking I/O channels with timeout and events generation
 *     capability.</li>
 * <li>Pre-emptive scheduling.</li>
 * <li>Minimal system requirements: about 8KiB ROM with all options enabled and
 *     speed optimizations on. The size can shrink under 2KiB by disabling the
 *     the unused subsystems and optimizing for size.</li>
 * <li>Small memory footprint, unused subsystems can be excluded by the
 *     memory image.</li>
 * <li>Almost totally written in C with little ASM code required for ports.</li>
 * </ul>
 *
 * ChibiOS/RT architecture:<br><br>
 * @subpage Concepts
 */

/**
 * @page Concepts Concepts
 * @{
 * @section naming Naming Conventions
 * ChibiOS/RT APIs are all named following this convention:
 * \a ch\<group\>\<action\>\<suffix\>().
 * The possible groups are: \a Sys, \a Sch, \a VT, \a Thd, \a Sem, \a Evt,
 * \a Msg, \a IQ, \a OQ, \a HQ,\a FDD, \a HDD.
 * The suffix is not present for normal APIs but can be one of
 * the following: "I" for APIs meant to be invoked from an interrupt handler
 * or within the system mutex zone but not from user code, "S" for APIs only
 * useable from within the system mutex zone but not from interrupt handlers
 * or user code. The APIs without suffix can be invoked only from the user
 * code.<br>
 * Examples: \p chThdCreate(), \p chSemSignalI(), \p chIQGetTimeout().
 *
 * @section scheduling Scheduling
 * The strategy is very simple the currently ready thread with the highest
 * priority is executed. If more than one thread with equal priority are
 * eligible for execution then they are executed in a round-robin way, the
 * CPU time slice constant is configurable. The ready list is a double linked
 * list of threads ordered by priority.
 * @image html readylist.png
 * Note that the currently running thread is not in the ready list, the list
 * only contains the threads ready to be executed but still actually waiting.
 *
 * @section warea Thread Working Area
 * Each thread has its own stack, a Thread structure and a registers dump
 * structure. All the structures are allocated into a "Thread working area",
 * a thread private heap, usually allocated in a char array declared in your
 * code, there is not a central threads table or list, this means you can
 * have as many threads you want as long you have enough available RAM
 * memory. The threads do not use any memory outside the allocated working
 * area.<br>

 * @image html workspace.png
 * <br>
 * Note that the registers dump is only present when the Thread is not
 * running, the context switching is done by pushing the registers on the
 * stack of the switched-out thread and popping the registers of the
 * switched-in thread from its stack.
 *
 * @section sysmutex System Mutex Zone
 * It is the code within the OS that cannot be preempted, this code is
 * everything between the \p chSysLock() and \p chSysUnlock() API calls.
 * The implementation of the APIs in most cases just enables/disables the
 * interrupts. Of course the code in the system mutex zone must be as short
 * and efficient possible as it affects the RT performance of the whole
 * system. The worst case response time is affected by the longest code
 * path in the system mutex zone or interrupt handler.
 * @code
 * // User code, not critical, preemption possible.
 * chSysLock();
 * ...
 * // System critical code, preemption delayed.
 * ...
 * chSysUnlock();
 * // User code, preemption possible again.
 * @endcode
 * Applications usually do not need to put code into the system mutex zone
 * unless you are implementing device drivers or special synchronization
 * primitives, everything else can be implemented by using semaphores,
 * messages or events.
 */
/** @} */

/**
 * @defgroup Kernel Kernel
 * @{
 */
/** @} */

/**
 * @defgroup Config Configuration
 * @{
 * In \p chconf.h are defined the required subsystems for your application.
 * @ingroup Kernel
 * @file chconf.h ChibiOS/RT configuration file.
 */
/** @} */

/**
 * @defgroup Core Core
 * @{
 * Non portable code.
 * @ingroup Kernel
 * @file chcore.c Non portable code.
 */
/** @} */

/**
 * @defgroup Initialization Initialization
 * @{
 * Initialization APIs and procedures.
 * @ingroup Kernel
 * @file ch.h ChibiOS/RT main include file, it includes everything else.
 * @file chinit.c ChibiOS/RT Initialization code.
 */
/** @} */

/**
 * @defgroup Debug Debug
 * @{
 * Debug APIs and procedures.
 * @ingroup Kernel
 * @file debug.h Debug macros and structures.
 * @file chdebug.c ChibiOS/RT Debug code.
 */
/** @} */

/**
 * @defgroup Scheduler Scheduler
 * @{
 * ChibiOS/RT scheduler.
 * @ingroup Kernel
 * @file chschd.c Scheduler code.
 * @file scheduler.h Scheduler macros and structures.
 */
/** @} */

/**
 * @defgroup Threads Threads
 * @{
 * Threads creation and termination APIs.
 * @file threads.h Threads structures, macros and functions.
 * @file chthreads.c Threads code.
 */
/** @} */

/**
 * @defgroup VirtualTimers Virtual Timers
 * @{
 * Virtual Timers APIs.
 * In order to use the Virtual Timers the \p CH_USE_VIRTUAL_TIMERS option
 * must be specified in \p chconf.h.
 * @file src/chdelta.c Virtual Timers code.
 * @file delta.h Virtual Timers macros and structures.
 */
/** @} */

/**
 * @defgroup Time Time
 * @{
 * Time related APIs.
 * In order to use the Time APIs the \p CH_USE_SLEEP
 * option must be specified in \p chconf.h.
 * @file include/sleep.h Time macros and structures.
 * @file chsleep.c Time functions.
 */
/** @} */

/**
 * @defgroup Semaphores Semaphores
 * @{
 * Semaphores and threads synchronization.
 * <b>Operation mode</b><br><br>
 * A semaphore is a threads synchronization object, some operations
 * are defined on semaphores:<br>
 * <ul>
 *   <li><b>Signal</b>: The semaphore counter is increased and if the result
 *     is non-positive then a waiting thread is removed from the semaphore
 *     queue and made ready for execution.
 *   </li>
 *   <li><b>Wait</b>: The semaphore counter is decreased and if the result
 *     becomes negative the thread is queued in the semaphore and suspended.
 *   </li>
 *   <li><b>Reset</b>: The semaphore counter is reset to a non-negative value
 *     and all the threads in the queue are released.
 *   </li>
 * </ul>
 * Semaphores can be used as guards for mutual exclusion code zones but
 * also have other uses, queues guards and counters as example.<br>
 * In order to use the Semaphores APIs the \p CH_USE_SEMAPHORES
 * option must be specified in \p chconf.h.<br><br>
 * @file semaphores.h Semaphores macros and structures.
 * @file chsem.c Semaphores code.
 */
/** @} */

/**
 * @defgroup Mutexes Mutexes
 * @{
 * Mutexes and threads synchronization.
 * <b>Operation mode</b><br><br>
 * A mutex is a threads synchronization object, some operations are defined
 * on mutexes:<br>
 * <ul>
 *   <li><b>Lock</b>: The mutex is checked, if the mutex is not owned by some
 *     other thread then it is locked else the current thread is queued on the
 *     mutex in a list ordered by priority.
 *   </li>
 *   <li><b>Unlock</b>: The mutex is released by the owner and the highest
 *     priority thread waiting in the queue, if any, is resumed and made owner
 *     of the mutex.
 *   </li>
 * </ul>
 * In order to use the Event APIs the \p CH_USE_MUTEXES option must be
 * specified in \p chconf.h.<br>
 *
 * <b>Constraints</b><br><br>
 * In ChibiOS/RT the Unlock operations are always performed in Lock-reverse
 * order. The Unlock API does not even have a parameter, the mutex to unlock
 * is taken from an internal stack of owned mutexes.
 * This both improves the performance and is required by the priority
 * inheritance mechanism.
 *
 * <b>The priority inversion problem</b><br><br>
 * The mutexes in ChibiOS/RT implements the <b>full</b> priority
 * inheritance mechanism in order handle the priority inversion problem.<br>
 * When a thread is queued on a mutex, any thread, directly or indirectly,
 * holding the mutex gains the same priority of the waiting thread (if their
 * priority was not already equal or higher). The mechanism works with any
 * number of nested mutexes and any number of involved threads. The algorithm
 * complexity (worst case) is N with N equal to the number of nested mutexes.
 * @file mutexes.h Mutexes macros and structures.
 * @file chmtx.c Mutexes functions.
 */
/** @} */

/**
 * @defgroup Events Events
 * @{
 * Event Sources and Event Listeners.<br>
 * <b>Operation mode</b><br><br>
 * An Event Source is a special object that can be signaled by a thread or
 * an interrupt service routine. Signaling an Event Source has the effect
 * that all the threads registered on the Event Source will receive
 * and serve the event.<br>
 * An unlimited number of Event Sources can exists in a system and each
 * thread can listen on an unlimited number of them.<br>
 * Note that the events can be asynchronously generated but are synchronously
 * served, a thread can serve event by calling the \p chEvtWait()
 * API. If an event is generated while a listening thread is not ready to
 * serve it then the event becomes "pending" and will be served as soon the
 * thread invokes the \p chEvtWait().<br>
 * In order to use the Event APIs the \p CH_USE_EVENTS option must be
 * specified in \p chconf.h.
 * @file events.h Events macros and structures.
 * @file chevents.c Events functions.
 */
/** @} */

/**
 * @defgroup Messages Messages
 * @{
 * Synchronous Messages.<br>
 * <b>Operation Mode</b><br><br>
 * Messages are an easy to use and fast IPC mechanism, threads can both serve
 * messages and send messages to other threads, the mechanism allows data to
 * be carryed in both directions. Data is not copyed between the client and
 * server threads but just a pointer passed so the exchange is very time
 * efficient.<br>
 * Messages are usually processed in FIFO order but it is possible to process
 * them in priority order by specifying \p P_MSGBYPRIO when creating a server
 * thread, \p CH_USE_MESSAGES_PRIORITY must also be specified in \p chconf.h
 * in order to enable the feature.<br>
 * Threads do not need to allocate space for message queues, the mechanism
 * just requires two extra pointers in the \p Thread structure (the message
 * queue header).<br>
 * In order to use the Messages APIs the \p CH_USE_MESSAGES option must be
 * specified in \p chconf.h.
 * @file messages.h	Messages macros and structures.
 * @file chmsg.c Messages functions.
 */
/** @} */

/**
 * @defgroup IOQueues I/O Queues
 * @{
 * ChibiOS/RT supports several kinds of queues. The queues are mostly used
 * in serial-like device drivers. The device drivers are usually designed to
 * have a lower side (lower driver, it is usually an interrupt service
 * routine) and an upper side (upper driver, accessed by the application
 * threads).<br>
 * There are several kind of queues:<br>
 * <ul>
 * <li><b>Input queue</b>, monodirectional queue where the writer is the
 *     lower side and the reader is the upper side.</li>
 * <li><b>Output queue</b>, monodirectional queue where the writer is the
 *     upper side and the reader is the lower side.</li>
 * <li><b>Half duplex queue</b>, bidirectional queue where the buffer is shared
 *     between a receive and a transmit queues. This means that concurrent
 *     buffered input and output operations are not possible, this is perfectly
 *     acceptable for a lot of applications however, as example an RS485 driver.
 * <li><b>Full duplex queue</b>, bidirectional queue where read and write
 *     operations can happen at the same time. Full duplex queues
 *     are implemented by pairing an input queue and an output queue together.
 * </ul>
 * In order to use the I/O queues the \p CH_USE_QUEUES option must
 * be specified in \p chconf.h.<br>
 * In order to use the half duplex queues the \p CH_USE_QUEUES_HALFDUPLEX
 * option must be specified in \p chconf.h.
 * @file queues.h I/O Queues macros and structures.
 * @file chqueues.c I/O Queues code.
 */
/** @} */

/**
 * @defgroup Serial Serial Drivers
 * @{
 * This module implements a generic full duplex serial driver and a generic
 * half duplex serial driver. It uses the I/O Queues for communication between
 * the upper and the lower driver and events to notify the application about
 * incoming data, outcoming data and other I/O events.
 * The  module also contains functions that make the implementation of the
 * interrupt service routines much easier.<br>
 * In order to use the serial full duplex driver the
 * \p CH_USE_SERIAL_FULLDUPLEX option must be specified in \p chconf.h.<br>
 * In order to use the serial half duplex driver the
 * \p CH_USE_SERIAL_HALFDUPLEX option must be specified in \p chconf.h.
 * @file serial.h Serial Drivers macros and structures.
 * @file chserial.c Serial Drivers code.
 */
/** @} */