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/*
ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010,
2011,2012,2013 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 concepts Kernel Concepts
* @brief ChibiOS/RT Kernel Concepts
* - @ref naming
* - @ref api_suffixes
* - @ref interrupt_classes
* - @ref system_states
* - @ref scheduling
* - @ref thread_states
* - @ref priority
* - @ref warea
* .
* @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 Time, @a VT, @a Thd, @a Sem,
* @a Mtx, @a Cond, @a Evt, @a Msg, @a Reg, @a SequentialStream, @a IO, @a IQ,
* @a OQ, @a Dbg, @a Core, @a Heap, @a Pool.
*
* @section api_suffixes API Name Suffixes
* The suffix can be one of the following:
* - <b>None</b>, APIs without any suffix can be invoked only from the user
* code in the <b>Normal</b> state unless differently specified. See
* @ref system_states.
* - @anchor I-Class <b>"I"</b>, I-Class APIs are invokable only from the
* <b>I-Locked</b> or <b>S-Locked</b> states. See @ref system_states.
* - @anchor S-Class <b>"S"</b>, S-Class APIs are invokable only from the
* <b>S-Locked</b> state. See @ref system_states.
* .
* Examples: @p chThdCreateStatic(), @p chSemSignalI(), @p chIQGetTimeout().
*
* @section interrupt_classes Interrupt Classes
* In ChibiOS/RT there are three logical interrupt classes:
* - <b>Regular Interrupts</b>. Maskable interrupt sources that cannot
* preempt (small parts of) the kernel code and are thus able to invoke
* operating system APIs from within their handlers. The interrupt handlers
* belonging to this class must be written following some rules. See the
* system APIs group and the web article
* <a href="http://chibios.sourceforge.net/dokuwiki/doku.php?id=chibios:howtos:interrupts">
* How to write interrupt handlers</a>.
* - <b>Fast Interrupts</b>. Maskable interrupt sources with the ability
* to preempt the kernel code and thus have a lower latency and are less
* subject to jitter, see the web article
* <a href="http://chibios.sourceforge.net/dokuwiki/doku.php?id=chibios:articles:jitter">
* Response Time and Jitter</a>.
* Such sources are not supported on all the architectures.<br>
* Fast interrupts are not allowed to invoke any operating system API from
* within their handlers. Fast interrupt sources may, however, pend a lower
* priority regular interrupt where access to the operating system is
* possible.
* - <b>Non Maskable Interrupts</b>. Non maskable interrupt sources are
* totally out of the operating system control and have the lowest latency.
* Such sources are not supported on all the architectures.
* .
* The mapping of the above logical classes into physical interrupts priorities
* is, of course, port dependent. See the documentation of the various ports
* for details.
*
* @section system_states System States
* When using ChibiOS/RT the system can be in one of the following logical
* operating states:
* - <b>Init</b>. When the system is in this state all the maskable
* interrupt sources are disabled. In this state it is not possible to use
* any system API except @p chSysInit(). This state is entered after a
* physical reset.
* - <b>Normal</b>. All the interrupt sources are enabled and the system APIs
* are accessible, threads are running.
* - <b>Suspended</b>. In this state the fast interrupt sources are enabled but
* the regular interrupt sources are not. In this state it is not possible
* to use any system API except @p chSysDisable() or @p chSysEnable() in
* order to change state.
* - <b>Disabled</b>. When the system is in this state both the maskable
* regular and fast interrupt sources are disabled. In this state it is not
* possible to use any system API except @p chSysSuspend() or
* @p chSysEnable() in order to change state.
* - <b>Sleep</b>. Architecture-dependent low power mode, the idle thread
* goes in this state and waits for interrupts, after servicing the interrupt
* the Normal state is restored and the scheduler has a chance to reschedule.
* - <b>S-Locked</b>. Kernel locked and regular interrupt sources disabled.
* Fast interrupt sources are enabled. @ref S-Class and @ref I-Class APIs are
* invokable in this state.
* - <b>I-Locked</b>. Kernel locked and regular interrupt sources disabled.
* @ref I-Class APIs are invokable from this state.
* - <b>Serving Regular Interrupt</b>. No system APIs are accessible but it is
* possible to switch to the I-Locked state using @p chSysLockFromIsr() and
* then invoke any @ref I-Class API. Interrupt handlers can be preemptable on
* some architectures thus is important to switch to I-Locked state before
* invoking system APIs.
* - <b>Serving Fast Interrupt</b>. System APIs are not accessible.
* - <b>Serving Non-Maskable Interrupt</b>. System APIs are not accessible.
* - <b>Halted</b>. All interrupt sources are disabled and system stopped into
* an infinite loop. This state can be reached if the debug mode is activated
* <b>and</b> an error is detected <b>or</b> after explicitly invoking
* @p chSysHalt().
* .
* Note that the above states are just <b>Logical States</b> that may have no
* real associated machine state on some architectures. The following diagram
* shows the possible transitions between the states:
*
* @if LATEX_PDF
* @dot
digraph example {
size="5, 7";
rankdir="LR";
node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
edge [fontname=Helvetica, fontsize=8];
init [label="Init", style="bold"];
norm [label="Normal", shape=doublecircle];
susp [label="Suspended"];
disab [label="Disabled"];
slock [label="S-Locked"];
ilock [label="I-Locked"];
slock [label="S-Locked"];
sleep [label="Sleep"];
sri [label="SRI"];
init -> norm [label="chSysInit()"];
norm -> slock [label="chSysLock()", constraint=false];
slock -> norm [label="chSysUnlock()"];
norm -> susp [label="chSysSuspend()"];
susp -> disab [label="chSysDisable()"];
norm -> disab [label="chSysDisable()"];
susp -> norm [label="chSysEnable()"];
disab -> norm [label="chSysEnable()"];
disab -> susp [label="chSysSuspend()"];
slock -> ilock [label="Context Switch", dir="both"];
norm -> sri [label="Regular IRQ", style="dotted"];
sri -> norm [label="Regular IRQ return", fontname=Helvetica, fontsize=8];
sri -> ilock [label="chSysLockFromIsr()", constraint=false];
ilock -> sri [label="chSysUnlockFromIsr()", fontsize=8];
norm -> sleep [label="Idle Thread"];
sleep -> sri [label="Regular IRQ", style="dotted"];
}
* @enddot
* @else
* @dot
digraph example {
rankdir="LR";
node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
edge [fontname=Helvetica, fontsize=8];
init [label="Init", style="bold"];
norm [label="Normal", shape=doublecircle];
susp [label="Suspended"];
disab [label="Disabled"];
slock [label="S-Locked"];
ilock [label="I-Locked"];
slock [label="S-Locked"];
sleep [label="Sleep"];
sri [label="SRI"];
init -> norm [label="chSysInit()"];
norm -> slock [label="chSysLock()", constraint=false];
slock -> norm [label="chSysUnlock()"];
norm -> susp [label="chSysSuspend()"];
susp -> disab [label="chSysDisable()"];
norm -> disab [label="chSysDisable()"];
susp -> norm [label="chSysEnable()"];
disab -> norm [label="chSysEnable()"];
disab -> susp [label="chSysSuspend()"];
slock -> ilock [label="Context Switch", dir="both"];
norm -> sri [label="Regular IRQ", style="dotted"];
sri -> norm [label="Regular IRQ return", fontname=Helvetica, fontsize=8];
sri -> ilock [label="chSysLockFromIsr()", constraint=false];
ilock -> sri [label="chSysUnlockFromIsr()", fontsize=8];
norm -> sleep [label="Idle Thread"];
sleep -> sri [label="Regular IRQ", style="dotted"];
}
* @enddot
* @endif
* Note, the <b>SFI</b>, <b>Halted</b> and <b>SNMI</b> states were not shown
* because those are reachable from most states:
*
* @dot
digraph example {
size="5, 7";
rankdir="LR";
node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
edge [fontname=Helvetica, fontsize=8];
any1 [label="Any State\nexcept *"];
sfi [label="SFI"];
any1 -> sfi [style="dotted", label="Fast IRQ"];
sfi -> any1 [label="Fast IRQ return"];
}
* @enddot
* @dot
digraph example {
size="5, 7";
rankdir="LR";
node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
edge [fontname=Helvetica, fontsize=8];
any2 [label="Any State"];
halt [label="Halted"];
SNMI [label="SNMI"];
any2 -> halt [label="chSysHalt()"];
any2 -> SNMI [label="Synchronous NMI"];
any2 -> SNMI [label="Asynchronous NMI", style="dotted"];
SNMI -> any2 [label="NMI return"];
halt -> SNMI [label="Asynchronous NMI", style="dotted"];
SNMI -> halt [label="NMI return"];
}
* @enddot
* @attention * except: <b>Init</b>, <b>Halt</b>, <b>SNMI</b>, <b>Disabled</b>.
*
* @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.<br><br>
* @if LATEX_PDF
* @dot
digraph example {
size="5, 7";
rankdir="LR";
node [shape=square, fontname=Helvetica, fontsize=8,
fixedsize="true", width="0.6", height="0.5"];
edge [fontname=Helvetica, fontsize=8];
subgraph cluster_running {
node [shape=square, fontname=Helvetica, fontsize=8,
fixedsize="true", width="0.6", height="0.5"];
currp [label="'currp'\npointer", style="bold"];
T4 [label="Tuser(4)\nprio=100"];
label = "Currently Running Thread";
penwidth = 0;
}
subgraph cluster_rlist {
node [shape=square, fontname=Helvetica, fontsize=8,
fixedsize="true", width="0.6", height="0.5"];
rh [label="ready list\nheader\nprio=0", style="bold"];
Ti [label="Tidle\nprio=1"];
Tm [label="Tmain\nprio=64"];
T1 [label="Tuser(1)\nprio=32"];
T2 [label="Tuser(2)\nprio=32"];
T3 [label="Tuser(3)\nprio=80"];
label = "Threads Ready for Execution";
penwidth = 0;
}
currp -> T4
rh -> Ti -> T1 -> T2 -> Tm -> T3 -> rh [label="p_next"];
rh -> T3 -> Tm -> T2 -> T1 -> Ti -> rh [label="p_prev"];
}
* @enddot
* @else
* @dot
digraph example {
rankdir="LR";
node [shape=square, fontname=Helvetica, fontsize=8,
fixedsize="true", width="0.6", height="0.5"];
edge [fontname=Helvetica, fontsize=8];
subgraph cluster_running {
node [shape=square, fontname=Helvetica, fontsize=8,
fixedsize="true", width="0.6", height="0.5"];
currp [label="'currp'\npointer", style="bold"];
T4 [label="Tuser(4)\nprio=100"];
label = "Currently Running Thread";
penwidth = 0;
}
subgraph cluster_rlist {
node [shape=square, fontname=Helvetica, fontsize=8,
fixedsize="true", width="0.6", height="0.5"];
rh [label="ready list\nheader\nprio=0", style="bold"];
Ti [label="Tidle\nprio=1"];
Tm [label="Tmain\nprio=64"];
T1 [label="Tuser(1)\nprio=32"];
T2 [label="Tuser(2)\nprio=32"];
T3 [label="Tuser(3)\nprio=80"];
label = "Threads Ready for Execution";
penwidth = 0;
}
currp -> T4
rh -> Ti -> T1 -> T2 -> Tm -> T3 -> rh [label="p_next"];
rh -> T3 -> Tm -> T2 -> T1 -> Ti -> rh [label="p_prev"];
}
* @enddot
* @endif
* <br>
* 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 thread_states Thread States
* The image shows how threads can change their state in ChibiOS/RT.<br>
* @if LATEX_PDF
* @dot
digraph example {
rankdir="LR";
node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
size="5, 7";
edge [fontname=Helvetica, fontsize=8];
start [label="Start", style="bold"];
run [label="Running"];
ready [label="Ready"];
suspend [label="Suspended"];
sleep [label="Sleeping"];
stop [label="Stop", style="bold"];
start -> suspend [label="\n chThdCreateI()", constraint=false, dir=back];
start -> run [label="chThdCreate()"];
start -> ready [label="chThdCreate()"];
run -> ready [label="Reschedule", dir="both"];
suspend -> run [label="chThdResume()"];
suspend -> ready [label="chThdResume()"];
run -> sleep [label="chSchGoSleepS()"];
sleep -> run [label="chSchWakepuS()"];
sleep -> ready [label="chSchWakepuS()"];
run -> stop [label="chThdExit()"];
}
* @enddot
* @else
* @dot
digraph example {
rankdir="LR";
node [shape=circle, fontname=Helvetica, fontsize=8, fixedsize="true", width="0.75", height="0.75"];
edge [fontname=Helvetica, fontsize=8];
start [label="Start", style="bold"];
run [label="Running"];
ready [label="Ready"];
suspend [label="Suspended"];
sleep [label="Sleeping"];
stop [label="Stop", style="bold"];
start -> suspend [label="\n chThdCreateI()", constraint=false, dir=back];
start -> run [label="chThdCreate()"];
start -> ready [label="chThdCreate()"];
run -> ready [label="Reschedule", dir="both"];
suspend -> run [label="chThdResume()"];
suspend -> ready [label="chThdResume()"];
run -> sleep [label="chSchGoSleepS()"];
sleep -> run [label="chSchWakepuS()"];
sleep -> ready [label="chSchWakepuS()"];
run -> stop [label="chThdExit()"];
}
* @enddot
* @endif
*
* @section priority Priority Levels
* Priorities in ChibiOS/RT are a contiguous numerical range but the initial
* and final values are not enforced.<br>
* The following table describes the various priority boundaries (from lowest
* to highest):
* - @p IDLEPRIO, this is the lowest priority level and is reserved for the
* idle thread, no other threads should share this priority level. This is
* the lowest numerical value of the priorities space.
* - @p LOWPRIO, the lowest priority level that can be assigned to an user
* thread.
* - @p NORMALPRIO, this is the central priority level for user threads. It is
* advisable to assign priorities to threads as values relative to
* @p NORMALPRIO, as example NORMALPRIO-1 or NORMALPRIO+4, this ensures the
* portability of code should the numerical range change in future
* implementations.
* - @p HIGHPRIO, the highest priority level that can be assigned to an user
* thread.
* - @p ABSPRO, absolute maximum software priority level, it can be higher than
* @p HIGHPRIO but the numerical values above @p HIGHPRIO up to @p ABSPRIO
* (inclusive) are reserved. This is the highest numerical value of the
* priorities space.
* .
* @section warea Thread Working Area
* Each thread has its own stack, a Thread structure and some preemption
* areas. All the structures are allocated into a "Thread Working Area",
* a thread private heap, usually statically declared in your code.
* Threads do not use any memory outside the allocated working area
* except when accessing static shared data.<br><br>
* @if LATEX_PDF
* @image latex workspace.eps
* @else
* @image html workspace.png
* @endif
* <br>
* Note that the preemption area is only present when the thread is not
* running (switched out), 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.
* The preemption area can be divided in up to three structures:
* - External Context.
* - Interrupt Stack.
* - Internal Context.
* .
* See the port documentation for details, the area may change on
* the various ports and some structures may not be present (or be zero-sized).
*/
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