284 lines
13 KiB
Plaintext
284 lines
13 KiB
Plaintext
/*
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ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio.
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This file is part of ChibiOS/RT.
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ChibiOS/RT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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ChibiOS/RT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* @page concepts Kernel Concepts
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* @brief ChibiOS/RT Kernel Concepts
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* - @ref naming
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* - @ref api_suffixes
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* - @ref interrupt_classes
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* - @ref system_states
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* - @ref scheduling
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* - @ref thread_states
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* - @ref priority
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* - @ref warea
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* .
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* @section naming Naming Conventions
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* ChibiOS/RT APIs are all named following this convention:
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* @a ch\<group\>\<action\>\<suffix\>().
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* The possible groups are: @a Sys, @a Sch, @a Time, @a VT, @a Thd, @a Sem,
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* @a Mtx, @a Cond, @a Evt, @a Msg, @a SequentialStream, @a IO, @a IQ, @a OQ,
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* @a Dbg, @a Core, @a Heap, @a Pool.
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*
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* @section api_suffixes API Names Suffixes
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* The suffix can be one of the following:
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* - <b>None</b>, APIs without any suffix can be invoked only from the user
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* code in the <b>Normal</b> state unless differently specified. See
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* @ref system_states.
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* - @anchor I-Class <b>"I"</b>, I-Class APIs are invokable only from the
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* <b>I-Locked</b> or <b>S-Locked</b> states. See @ref system_states.
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* - @anchor S-Class <b>"S"</b>, S-Class APIs are invokable only from the
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* <b>S-Locked</b> state. See @ref system_states.
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* .
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* Examples: @p chThdCreateStatic(), @p chSemSignalI(), @p chIQGetTimeout().
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*
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* @section interrupt_classes Interrupt Classes
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* In ChibiOS/RT there are three logical interrupt classes:
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* - <b>Regular Interrupts</b>. Maskable interrupt sources that cannot
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* preempt (small parts of) the kernel code and are thus able to invoke
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* operating system APIs from within their handlers. The interrupt handlers
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* belonging to this class must be written following some rules. See the
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* @ref system APIs group and @ref article_interrupts.
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* - <b>Fast Interrupts</b>. Maskable interrupt sources with the ability
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* to preempt the kernel code and thus have a lower latency and are less
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* subject to jitter, see @ref article_jitter. Such sources are not
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* supported on all the architectures.<br>
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* Fast interrupts are not allowed to invoke any operating system API from
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* within their handlers. Fast interrupt sources may, however, pend a lower
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* priority regular interrupt where access to the operating system is
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* possible.
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* - <b>Non Maskable Interrupts</b>. Non maskable interrupt sources are
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* totally out of the operating system control and have the lowest latency.
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* Such sources are not supported on all the architectures.
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* .
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* The mapping of the above logical classes into physical interrupts priorities
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* is, of course, port dependent. See the documentation of the various ports
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* for details.
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*
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* @section system_states System States
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* When using ChibiOS/RT the system can be in one of the following logical
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* operating states:
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* - <b>Init</b>. When the system is in this state all the maskable
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* interrupt sources are disabled. In this state it is not possible to use
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* any system API except @p chSysInit(). This state is entered after a
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* physical reset.
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* - <b>Normal</b>. All the interrupt sources are enabled and the system APIs
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* are accessible, threads are running.
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* - <b>Suspended</b>. In this state the fast interrupt sources are enabled but
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* the regular interrupt sources are not. In this state it is not possible
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* to use any system API except @p chSysDisable() or @p chSysEnable() in
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* order to change state.
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* - <b>Disabled</b>. When the system is in this state both the maskable
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* regular and fast interrupt sources are disabled. In this state it is not
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* possible to use any system API except @p chSysSuspend() or
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* @p chSysEnable() in order to change state.
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* - <b>Sleep</b>. Architecture-dependent low power mode, the idle thread
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* goes in this state and waits for interrupts, after servicing the interrupt
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* the Normal state is restored and the scheduler has a chance to reschedule.
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* - <b>S-Locked</b>. Kernel locked and regular interrupt sources disabled.
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* Fast interrupt sources are enabled. @ref S-Class and @ref I-Class APIs are
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* invokable in this state.
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* - <b>I-Locked</b>. Kernel locked and regular interrupt sources disabled.
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* @ref I-Class APIs are invokable from this state.
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* - <b>Serving Regular Interrupt</b>. No system APIs are accessible but it is
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* possible to switch to the I-Locked state using @p chSysLockFromIsr() and
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* then invoke any @ref I-Class API. Interrupt handlers can be preemptable on
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* some architectures thus is important to switch to I-Locked state before
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* invoking system APIs.
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* - <b>Serving Fast Interrupt</b>. System APIs are not accessible.
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* - <b>Serving Non-Maskable Interrupt</b>. System APIs are not accessible.
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* - <b>Halted</b>. All interrupt sources are disabled and system stopped into
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* an infinite loop. This state can be reached if the debug mode is activated
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* <b>and</b> an error is detected <b>or</b> after explicitly invoking
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* @p chSysHalt().
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* .
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* Note that the above states are just <b>Logical States</b> that may have no
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* real associated machine state on some architectures. The following diagram
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* shows the possible transitions between the states:
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*
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* @dot
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digraph example {
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rankdir="LR";
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node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
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edge [fontname=Helvetica, fontsize=8];
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init [label="Init", style="bold"];
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norm [label="Normal", shape=doublecircle];
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susp [label="Suspended"];
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disab [label="Disabled"];
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slock [label="S-Locked"];
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ilock [label="I-Locked"];
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slock [label="S-Locked"];
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sleep [label="Sleep"];
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sri [label="SRI"];
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init -> norm [label="chSysInit()"];
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norm -> slock [label="chSysLock()", constraint=false];
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slock -> norm [label="chSysUnlock()"];
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norm -> susp [label="chSysSuspend()"];
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susp -> disab [label="chSysDisable()"];
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norm -> disab [label="chSysDisable()"];
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susp -> norm [label="chSysEnable()"];
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disab -> norm [label="chSysEnable()"];
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slock -> ilock [label="Context Switch", dir="both"];
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norm -> sri [label="Regular IRQ", style="dotted"];
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sri -> norm [label="Regular IRQ return", fontname=Helvetica, fontsize=8];
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sri -> ilock [label="chSysLockFromIsr()", constraint=false];
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ilock -> sri [label="chSysUnlockFromIsr()", fontsize=8];
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norm -> sleep [label="Idle Thread"];
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sleep -> sri [label="Regular IRQ", style="dotted"];
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}
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* @enddot
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* Note, the <b>SFI</b>, <b>Halted</b> and <b>SNMI</b> states were not shown
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* because those are reachable from most states:
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*
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* @dot
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digraph example {
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rankdir="LR";
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node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
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edge [fontname=Helvetica, fontsize=8];
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any1 [label="Any State\nexcept *"];
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any2 [label="Any State"];
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sfi [label="SFI"];
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halt [label="Halted"];
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SNMI [label="SNMI"];
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any1 -> sfi [style="dotted", label="Fast IRQ"];
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sfi -> any1 [label="Fast IRQ return"];
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any2 -> halt [label="chSysHalt()"];
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any2 -> SNMI [label="Synchronous NMI"];
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any2 -> SNMI [label="Asynchronous NMI", style="dotted"];
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SNMI -> any2 [label="NMI return"];
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halt -> SNMI [label="Asynchronous NMI", style="dotted"];
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SNMI -> halt [label="NMI return"];
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}
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* @enddot
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* @attention * except: <b>Init</b>, <b>Halt</b>, <b>SNMI</b>, <b>Disabled</b>.
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*
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* @section scheduling Scheduling
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* The strategy is very simple the currently ready thread with the highest
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* priority is executed. If more than one thread with equal priority are
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* eligible for execution then they are executed in a round-robin way, the
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* CPU time slice constant is configurable. The ready list is a double linked
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* list of threads ordered by priority.<br><br>
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* @dot
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digraph example {
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rankdir="LR";
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node [shape=square, fontname=Helvetica, fontsize=8,
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fixedsize="true", width="0.6", height="0.5"];
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edge [fontname=Helvetica, fontsize=8];
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subgraph cluster_running {
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node [shape=square, fontname=Helvetica, fontsize=8,
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fixedsize="true", width="0.6", height="0.5"];
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currp [label="'currp'\npointer", style="bold"];
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T4 [label="Tuser(4)\nprio=100"];
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label = "Currently Running Thread";
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penwidth = 0;
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}
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subgraph cluster_rlist {
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node [shape=square, fontname=Helvetica, fontsize=8,
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fixedsize="true", width="0.6", height="0.5"];
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rh [label="ready list\nheader\nprio=0", style="bold"];
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Ti [label="Tidle\nprio=1"];
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Tm [label="Tmain\nprio=64"];
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T1 [label="Tuser(1)\nprio=32"];
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T2 [label="Tuser(2)\nprio=32"];
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T3 [label="Tuser(3)\nprio=80"];
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label = "Threads Ready for Execution";
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penwidth = 0;
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}
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currp -> T4
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rh -> Ti -> T1 -> T2 -> Tm -> T3 -> rh [label="p_next"];
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rh -> T3 -> Tm -> T2 -> T1 -> Ti -> rh [label="p_prev"];
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}
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* @enddot
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* <br>
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* Note that the currently running thread is not in the ready list, the list
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* only contains the threads ready to be executed but still actually waiting.
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*
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* @section thread_states Threads States
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* The image shows how threads can change their state in ChibiOS/RT.<br>
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* @dot
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digraph example {
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/*rankdir="LR";*/
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node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
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edge [fontname=Helvetica, fontsize=8];
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start [label="Start", style="bold"];
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run [label="Running"];
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ready [label="Ready"];
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suspend [label="Suspended"];
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sleep [label="Sleeping"];
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stop [label="Stop", style="bold"];
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start -> suspend [label="chThdInit()", constraint=false];
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start -> run [label="chThdCreate()"];
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start -> ready [label="chThdCreate()"];
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run -> ready [label="Reschedule", dir="both"];
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suspend -> run [label="chThdResume()"];
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suspend -> ready [label="chThdResume()"];
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run -> sleep [label="chSchGoSleepS()"];
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sleep -> run [label="chSchWakepS()"];
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sleep -> ready [label="chSchWakepS()"];
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run -> stop [label="chThdExit()"];
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}
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* @enddot
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*
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* @section priority Priority Levels
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* Priorities in ChibiOS/RT are a contiguous numerical range but the initial
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* and final values are not enforced.<br>
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* The following table describes the various priority boundaries (from lowest
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* to highest):
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* - @p IDLEPRIO, this is the lowest priority level and is reserved for the
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* idle thread, no other threads should share this priority level. This is
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* the lowest numerical value of the priorities space.
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* - @p LOWPRIO, the lowest priority level that can be assigned to an user
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* thread.
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* - @p NORMALPRIO, this is the central priority level for user threads. It is
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* advisable to assign priorities to threads as values relative to
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* @p NORMALPRIO, as example NORMALPRIO-1 or NORMALPRIO+4, this ensures the
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* portability of code should the numerical range change in future
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* implementations.
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* - @p HIGHPRIO, the highest priority level that can be assigned to an user
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* thread.
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* - @p ABSPRO, absolute maximum software priority level, it can be higher than
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* @p HIGHPRIO but the numerical values above @p HIGHPRIO up to @p ABSPRIO
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* (inclusive) are reserved. This is the highest numerical value of the
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* priorities space.
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* .
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* @section warea Threads Working Area
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* Each thread has its own stack, a Thread structure and some preemption
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* areas. All the structures are allocated into a "Thread Working Area",
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* a thread private heap, usually statically declared in your code.
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* Threads do not use any memory outside the allocated working area
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* except when accessing static shared data.<br><br>
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* @image html workspace.png
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* <br>
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* Note that the preemption area is only present when the thread is not
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* running (switched out), the context switching is done by pushing the
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* registers on the stack of the switched-out thread and popping the registers
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* of the switched-in thread from its stack.
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* The preemption area can be divided in up to three structures:
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* - External Context.
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* - Interrupt Stack.
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* - Internal Context.
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* .
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* See the @ref core documentation for details, the area may change on
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* the various ports and some structures may not be present (or be zero-sized).
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*/
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