Introduction à la programmation temps-réel pour la...

Ludovic Saint-Bauzel01/10/2012

Introduction à la programmation temps-réel pour la robotique

Robotics Real-Time Programming

Ludovic Saint-Bauzel

Polytech’Paris UPMC

2012-2013

Ludovic Saint-Bauzel (Polytech’Paris UPMC) Robotics Real-Time Programming 2012-2013 1 / 334

Robotics Real-Time Programming

Ludovic Saint-Bauzel

Polytech’Paris UPMC

2012-2013

Introduction

Robotics Software Frameworks

OS : Tasks And Threads

OS Driver Programming

Application

Documentations


Introduction What is a robot ?

Layout

IntroductionWhat is a robot ?

DefinitionHardwareSoftware

First Idea : From ScratchSecond Idea : Operating System Approach




Application

DocumentationsLudovic Saint-Bauzel (Polytech’Paris UPMC) Robotics Real-Time Programming 2012-2013 4 / 334


Robot

I Definition : An Autonomous Robot is acomplex system that has the ability todecide its actions on its environmentfrom its sensing, state in order to fill hisaims. Survive, Assist ...

I SensorsI DecisionI Action

I Physical ability : read information fromsensor, send orders to actuators, have aregulation (Time based computation)and a decision computation unit(policy).

Effectors

Control

Sensors

Robot Environment

Supervision / Decision

Effectors

Decision

Sensors

Autonomous Robot Environment

Figure: Classic (up) andAutonomous (down) Robot Models



Robot : Computer science point of view

A computer science way to see a robot is to say it is a computer withperipherals that bring sensing, actuation ability and because of real lifeinteraction need to put the stress on the time. So like a computer we willhave to deal with :

I busI memoryI cpu



Structure Choice criteria

I Critical path?I the main loopI delayed sensors

I MethodI TasksI Pipes (read only, read write, write)

I ParametersI ComputationI Time constraintsI Memory needsI Precision of measure



Monocomputer

I PropertiesI Limited Computation AbilityI Delays are limited tooI Simple but efficient

I Recent ImprovementsI GPUI Multicore CPU

I ExampleFigure: mc2e



Monocomputer

I PropertiesI Limited Computation AbilityI Delays are limited tooI Simple but efficient

I Recent ImprovementsI GPUI Multicore CPU

I Example

Effectors

Control

Sensors

Robot


-Acquisition Card (NI-PCI6034E)

analog inputs (sensors),

analog outputs (effectors)

Figure: mc2e Architecture



Multi computer

I PropertiesI High scalability of

computationI High time lost : Bus

communicationI Recent Improvement

I Distributed algorithmsdeveloppment

I Example Staubli



Multi computer

I PropertiesI High scalability of

computationI High time lost : Bus

communicationI Recent Improvement

I Distributed algorithmsdeveloppment

I Example

Effectors

Control

Sensors

Robot


Robot Models

- Kinematics

- Velocities

Trajectory Control

GUI To choose

trajectories

UDP

Staubli



Master Computer - Slave Computing Units

I Master is connected to slave unitI Often a busI Image



Bus

I DefinitionI Physical connectionI Multiple devices

I Common elements :I Base Address called portsI Local Address

I Examples :I Serial

I RS485I USBI CAN

I ParallelI ISAI PCII ...



How the robot can make environment interaction ?

I CategoriesI PerceptionI DecisionI Actions

I Computer Science Name : tasks



Real-Time Programming

I Low Level AccessI High Time constraints

I Don’t mean quick!I Mean ability to respect those constraints



Low Level Programming

LINUX

#include ...unsigned char inb (unsigned short port) ;void outb (unsigned char byte , unsigned short port) ;unsigned char insb (unsigned short port , void *addr ,

unsigned long count) ;void outsb (unsigned short port , void *addr ,

unsigned long count) ;

DOS

#include ...unsigned char inputb (unsigned short port) ;void outputb (unsigned short port ,unsigned char byte) ;


Introduction First Idea : From Scratch

Layout

IntroductionWhat is a robot ?First Idea : From Scratch

Examplex86 exampleFrom scratch approach

Second Idea : Operating System Approach




Application



RobModex

I ISA CardI 0x100 : Base AddressI 0x01 - 0x04 : Timer (IRQ 5)I 0x05 - 0x08 : DAC1I 0x09 - 0x12 : DAC2I 0x13 - 0x14 : 2 Wheel Encoder Registers



Closed Loop PID

PID Controller Robot

qdes

qmes

error

variables qmes , qdeserror(k) =error_cumul(k) =error_diff(k)=

qcons=olderror = error



Simple IRQ x86

#0

IRQ IRR

#1

#2

#3

IMR ISR

0

0

0

0

0

1

0

0

0

0

0

0

IVT

Addr Interrupt Routine

PIC Registers Memory (0x0-0x3FF)

...

...

...



Simple IRQ x86

#0

IRQ IRR

#1

#2

#3

IMR ISR

1

0

0

0

0

1

0

0

0

0

0

0

IVT



...

...

...

?



Simple IRQ x86

#0

IRQ IRR

#1

#2

#3

IMR ISR

1

0

0

0

0

1

0

0

1

0

0

0

IVT



...

...

...



Simple IRQ x86

#0

IRQ IRR

#1

#2

#3

IMR ISR

0

0

0

0

0

1

0

0

0

0

0

0

IVT



...

...

...

I 0x20I Command RegisterI Status Register

I 0x21I Int Mask Register

I Internal RegistersI Int. Req. Reg.I In Service Register

I System MemoryI Interrupt Vector Table (4 bytes)I Byte 0 : Offset Low Address of the Interrupt Routine (Handler)I Byte 1 : Offset High Address of the IRI Byte 2 : Segment Low Address of the IRI Byte 3 : Segment High Address of the IR Offset



Piece of code :

turboC DOS example

#define IMR 0x21void _install_int_function(int IRQn ,

void interrupt (* _new_int_function )()){int inter = IRQn + 8;_disable (); // disable interrupts//save the old interrupt vector_old_int_function=_dos_getvect(inter);// install the new interrupt vector_dos_setvect(inter ,_new_int_function );//save the state of the 8259A IMR register_old_mask=inportb(IMR);//Set new value for IMR registeroutportb(IMR ,_old_mask&_interrupt_mask(IRQn ));_enable (); // enable interrupts

}



I/O APIC : Advanced Programmable Interrupt Controller



IRQ



Bus : ISA

I Ax : AddressesI Dx : DataI IRQs : 3,4,5,6,7I AEN : DMA

Figure: ISA Port



Bus : ISA

#define ISAADDRshort data;void interrupt _new_int_function (){

_disable (); // disable interruptsdata=inb(ISAADDR ); // getDataFromISA//that the ISA Component has requested//to tell the system the interrupt service function has finished_end_interrupt ();_enable (); // enable interrupts again}



Digital/Analog Converter

Figure: Digital Analog Converter Schematic



RobModex Application

#define ISAADDR .....short data;

void interrupt _new_int_function (){_disable (); // disable interruptsdata=inb( );

outb( , );_end_interrupt ();_enable (); // enable interrupts again}



Conclusion

I More Complex = More codeI No- reusability of pieces of code

Figure: RUPI


Introduction Second Idea : Operating System Approach

Layout

IntroductionWhat is a robot ?First Idea : From ScratchSecond Idea : Operating System Approach

IntroductionPropertiesSimpleMultitasksReal-Time




Application

Documentations



Operating System few words

A software :or precisely the first software executed by your computer Consequences :Manager

I Schedule task orderI Manage resources in order to fulfil every needsI Use of all the resources.



Resources

Computer Science :I Processor : CPU, IRQI Communication : BUSI MemoryI ...

Robotics :I MotorI Sensors



What is RealTime

Two examples :

A navigation system computing the best path for a boat.

A navigation system computing a boat position during its sailing.

I First case: Computing time is not a constraint, the result is this onlything that is interesting

I Second case, if computing time is too long, position is false.



An informal definition

Real-Time system : A system where the behaviour relies on precision ofcomputation and also the time when it is produced.

In other words, a delay is considered as an error that can lead to severeconsequences



A Robotic definition

A Real-Time System: a system that bring possibility to control a robotin a finite time and let us manage urgent informations in a high level ofpriority. That means a real time system for control and management of

events with priority possibilities.



Deadline and realtime system

Different kind of deadlineI Hard Deadline : a delay generate an exception (error event and

computation)I Soft Deadline : a delay don’t lead to an exception

Different possible real-time systemsI Hard Real-Time systems : exceeded deadlines must not arise.

(VxWorks, RT-Linux, RTAI, Xenomai...)I Soft Real-Time : exceeded deadlines can sometimes happen. (DOS,

Microsoft Robotic Studio?)



Environment and RealTime System

System : set of activities linked to one or more computing tasks that aredone sequentially or concurrently and that can communicate each other.

A Real-Time System interacts in its environmentI Sensors : signals and their measurement toolsI Computing UnitI Actuators : act on the environment at precise times



Approaches

Centralised

I A CPU work on information coming from sensors and send the resultto actuators

Multiple-systems

I Controlled systems and a controlling system interacting with sensorsand actuators



Time scheduling

I time-driven system : measure of time leads to actionsI event-driven system : arising of an event leads to actionsI reactive system : constrained time to process



Predictability determinism reliability

Real time system : in worst case.

Predictability : Ability to identify in advance if a system is able to respectits time constraints Knowledge of parameters related to computation.

Determinism : remove any uncertainty in individual task behaviour andwhen they are together

I Variation of task execution timeI IO duration, reaction timeI Interruption reaction

Reliability : Behaviour and Fault tolerance



Example GSM Mobile

System must combine :I Hardware layer : emission, reception, voice coder activation, reception

strength measure, etcI Software layer : DB communication for localisation update, look up

calling messages, etc...Real-Time constraints : 577 µs of talking emitted and reception every 4,6ms

Mobility constraints : emits with a earlier signal if distance increase andlater if it decreases.System must be enough reactive in order to the system comfortable for theuser.



Classical system limits

Classical systems are based on multiple task not well adapted to real timeconstraints :

I scheduling policy that aims to share time in a balance way for eachtask

I access mechanisms that shares resources and synchronizes timeuncertainty

I interruption management is not optimalI Virtual memory and cache memory management generate some delaysI timer management is not very accurate



Services

Let’s consider a simple system :

I a single softwareI One CPUI One memoryI One IO controllerI One communication bus

Software interacts with external world

I Data acquisitionI ComputationI Returning the results

How can a software react to an event that can arise at any time?



Cyclic look up

Look up regularly each peripheral devices : called interacting from acyclic look up

dodocheck sensorswhile (no data are available)read sensorscompute datadoactivate actuatorswhile (action to do)while (system halts)



Cyclic look up

ProsI predictable : one iteration time (easy to know)I easy to program : with a few peripheral devices while reaction time of

each device are almost the sameCons

I if there is many devices and reaction time are very different,sub-optimal (near the slower device), sub loop to treat each device

I bad in a computer science point of view : software becomeunreadable, close to be impossible to maintain : a new device needs torewrite almost all the software.



Interruptions

How to warn the software that something happens outside? mechanism tostop the regular computation is called interruption

I Initially hardware event leads to some changing in softwarecomputation

I Next, extended to internal events and events coming from softwareI In general point of view, an event modify the behaviour of your

softwareDeal with interruptions

I Save contextI Interruption is computedI Restore context



Interruptions

dodocheck sensorswhile (WA_DATA)read memorised datawhile (system halts)

INTERRUPTION //from a sensorread datawrite WA_DATA is trueacknowledge interruption

I Interruption deals with external eventsI Cyclic look up software is delayedI Good response time if interruption

computation needs a few time



Limits

CPU can spend time to compute different things than the software

Example : UART (Universal Asynchronous Receiver Transmitter)

I Interruptions to emit and receive through two registers (parallelcomputation ability)

I Emission of a ASCII Char every millisecond : a lot time to wait untilwe have to emit again

I For a new emission : WAITI When UART is available : Interruption SIGNALI Software can restart

Can do new things while waiting : multiple-task



Synchronous or asynchronous approaches

I need a system that manage the software : start and synchronizes tasksaccording to events and context evolution

I 2 kind of approach :I synchronous one : direct link between a task and its activating

device, without taking care of conflicts that can arise between this taskand the others during execution of the software.

I asynchronous one : all events are considered, including duringcomputation of a task and reacts according to the context.



Synchronous approach

I "simple" algorithmI does not work without behavioural and time error emission

I No pre-emption neither concurrent access to share resourcesI "synchronous" hypothesis : task activating time is NULL

(instantaneous reaction)

I discrete time view, scheduled by events arising, in the opposite ofcontinuous time view (hard time)

I simultaneity linked to observation of current events at the same timeI simple and powerful model



Asynchronous approach

I more complex algorithms to implementI hard to model for checking the behaviour, need to evaluate every

possible pre-emptionI scheduling policy : event appearance, CPU load decision between :

I activated task by eventI running task when event ariseI another task waiting for the CPU

I sometimes it is possible to check off-line according to formal rulesI priority definition is based on some criteria like : deadline, period, level

of importance



Services of a multitasks system

Conclusion : A single program rarely use all CPU load

Used those idle times to compute some concurrent other tasks from othersoftware : a part of what an operating system must do

I running concurrent tasksI exchanging with outside worldI managing memory resourcesI sharing hardware, synchronization, communicationI time management

What are the limits for real-time system?



CPU Management - Task, process

Standard operating systems manage process that can be described asfollow :

I separated memory roomI special channels for communicationI high time cost spent for creation of a new oneI protection mechanisms are also time costingI switch between two processes need a lot of memory switches



CPU Management - Task, process

One process works on many memory areasI computing area (instructions of the software)I a heap data areaI a stack area for temporary data (variable)

Context of a process is composed of registers, a name, a state, etc.

A thread only own individual context data , everything else is shared withfather process



Management multiple task and scheduling

A activated process can have manystates, here are the main one :

I createdI terminatedI running : task is currently using

the CPU. We say it is elected.I waiting : task is asking for

CPU. It is electable.I blocked : task is blocked

waiting for an event to arise.

Created Terminated

Running

Waiting Blocked

Swapped out and waiting Swapped out and blocked

Main Memory

Virtual Memory



Management multiple task and scheduling

State transitions are :I waking : blocked → waitingI allocating : waiting → runningI unallocating or pre-empted :

running → waitingI blocking : running → blocked

Created Terminated

Running

Waiting Blocked

Swapped out and waiting Swapped out and blocked

Main Memory

Virtual Memory



Scheduling

Scheduler must manage how the task are allocated to the CPU.Schedule in the best way is very hard.A scheduler called with request or pre-emptive if running process can beunallocated by scheduler.Non pre-emptive systems can do context switch only when a task isterminated or when it is asking for context switchScheduler works most of the time on-line. That means that a policy mustexists and be applied



Scheduling policy

Classical scheduling rules :I First In First Out (FIFO)I Each one its turn (tourniquet, Round Robin : RR)I Priority based

Example

Task Length Priority Start timeT1 6 1 0T2 3 2 0T3 4 1 0



Scheduling example 1

I FIFOT1 T1 T1 T1 T1 T1 T2 T2 T2 T3 T3 T3 T3

I RR

T1 T2 T3 T1 T2 T3 T1 T2 T3 T1 T3 T1 T1

I Priority

T2 T2 T2 T1 T1 T1 T1 T1 T1 T3 T3 T3 T3




Scheduler with task interactionsTask 1 (prio = 2) Task 2 (prio = 2) Task 3 (prio = 3)

(not started)T[1.1] T[2.1] T[3.1]wait (event) Signal wait (1 sec.)T[1.2] (Task 1, event)

T[2.2] T[3.2]Starting Task 3




Pre-emption after OS signalTask 1 (prio = 2) Task 2 (prio = 2) Task 3 (prio = 3)T[1.1]Wait (evt)

T[2.1] Signal T1T[1.2]

T[2.2] Start T3T[3.1] Wait 1 sec.T[3.2]




Without pre-emptionTask 1 (prio = 2) Task 2 (prio = 2) Task 3 (prio = 3)T[1.1]Wait (evt)

T[2.1] Signal T1T[2.2] Start T3

T[3.1] Wait 1 sec.T[1.2]

T[3.2]



Interruptions

I 2 kindI asynchronous : emitted by external context (hardware) can arise at

any timeI synchronous : emitted by a specific instruction can only arrive in

known date for the developer

I processed by the same mechanism



Interruption management

The way interruptions are processed have a large influence on efficiency ofthe OS

I Control of interruptions : mostly hardwareI Context switchI Source identification

I Processing interruptionI Short : same contextI Long : task are called : signal/wait

I Back to original process



Resources management

Those mechanisms are used to give one access to one resource in one time.I Define some sections as atomic : critical sectionsI Mask interruptions (hardware)I Scheduler is disabled during this critical section (software)

I MutexI Block other tasks whatever priority they areI Problem to choose the task when Mutex is released

I Counting Semaphores to manage a set of devices



Synchronization

Force an order of processing instructions of a processI MutexI RendezvousI Product/Consume

Uses the following mechanisms :I Signal an eventI Semaphores useI MailboxesI Rendezvous



Synchronization Limits

Maintain coherency of data : creation of waiting queues

I "Balanced" Systems inefficientI Priority : Synchronization brings some priority issues where a low

priority can block a high priority task

Some solutions :I Priority based waiting management : unlock view the priority level of

the taskI Flag like "availability test"I Time out on blocking flags



Input/Output

Different policies for CPU scheduling and for Input/Output (IO)I Access through a specialized layerI Synchronous processingI Asynchronous processingI Difficult to manage prioritiesI Bad time management



Services

I Definition : a software that schedules computing of tasks in one shotway,manage devices of the system and bring development libraries(Application Programming Interface or API)

I It is organized with :I a kernel that schedules tasks and manage devicesI often it proposes services packaged as modules for example. These

service can bring the ability of the system to manage File Systems,network devices or any services that are needed by software



Components

The main components of a RTOS are :I scheduler, inside every kernel, it is the component that apply different

algorithms to manage access to the CPUI kernel interfaces that give developers the ability to create software

I tasksI semaphoresI message queue...

I services : actions that a kernel can do on a device or on the systemlike time measurement, interruption, bus controller,...


Robotics Software Frameworks RUPI

Layout

Introduction

Robotics Software FrameworksRUPI

RUPI Point Of ViewDesign PatternOROCOSROSFrameworks



Application


Robotics Software Frameworks RUPI

Challenging Scenario

Figure: RUPI


Robotics Software Frameworks Design Pattern

Layout

Introduction

Robotics Software FrameworksRUPIDesign Pattern

Software RecipesOROCOSROSFrameworks



Application



Find the tasks!

I No Fuzzy propertiesI Real-TimeI Good Refresh rate

I Nothing is perfectI Properties

I Time (Loop (Freq?), Oneshot)I Load (CPU)

I BoundariesI DelaysI Memory

I Task repeated every miliseconds with acceptable delay of 0.01 ms



Classical Robotics Tasks

I Control TaskI Loop, DelayI Variable ParametersI Static parameters

I User InterfaceI SupervisionI Send Orders (Asynchronous, Parameters)



MVC

I ViewI SupervisionI GUI

I ControllerI Send OrdersI Control Task InformationI GUI

I ModelI SynchronizationI Communication SystemI Database

I RT Task


Robotics Software Frameworks OROCOS

Layout

Introduction

Robotics Software FrameworksRUPIDesign PatternOROCOS

Open RObotics COntrol SoftwareROSFrameworks



Application



OROCOS Project

Figure: Orocos Project



History

I December 2000, as an idea of Herman BruyninckxI European FundingI European Labs

I K.U.Leuven in Belgium ( Orocos@KUL )I LAAS Toulouse in France ( Orocos@LAAS )I KTH Stockholm in Sweden ( Orocos@KTH )



Orocos Toolchain = RTT + OCL

I Real-Time ToolkitI Orocos Component Library

Figure: Orocos Component/PluginsArchitecture



Figure: RTT WorkflowLudovic Saint-Bauzel (Polytech’Paris UPMC) Robotics Real-Time Programming 2012-2013 82 / 334


Task Context

Figure: Component Description



OCL -> Logging Tools

I 2 SolutionsI Custom Component

I + Complete control of the generated fileI - Some additional code that is not the heart of the controller

I Listen a component through logging toolsI In C++ code :I In deployment :I



Task State Diagram

Figure: Component State DiagramLudovic Saint-Bauzel (Polytech’Paris UPMC) Robotics Real-Time Programming 2012-2013 85 / 334


Activity vs Threads

Figure: Component Activity Diagram



Data Flow

Figure: Components Connections



Example : Definition

I SupervisorI InitialisationI WaitingI Standing-UpI WalkingI Alert

I SensorsI Force HandlesI Orientation of the armI Orientations of the

wheels(Beta_L,Theta_L,Beta_R,Theta_R)

I ControlsI Impedance ControlI Position ControlI Speed ControlI Models

I XZ MGDI XYPhi MGDI Trajectory Generator Figure: Walky ISIR



Example : Modelling State Machine



Example : Modelling Data Flows



Example : State Machine (Excerpt)

StateMachine OurStateMachineType{

var bool detected;initial state INIT {

entry {ConsoleOut.display ("[ INIT ]");/*...*/ Plant.configure ();

}transition select Waiting;

}state Waiting {

entry {STSDetector.start ();

}transition STSDetected(detected)

if (detected) then select SitToStand;} /*...*/RootMachine OurStateMachineType statemachine



Example : Component Skeleton(Excerpt)

class Supervisor : public TaskContext {protected:

InputPort STSDetected; /*...*/string stateMachineName;

public:Supervisor(string const& name) : TaskContext(name),

stateMachineName (" statemachine "){

this ->addEventPort (" STSDetected",STSDetected );this ->addProperty (" stateMachineName",stateMachineName );

}

bool configureHook () {return true;

}void updateHook () { }void errorHook () { }void stopHook () { }void cleanupHook () { }};



Example : Deployment File(Excerpt)

0.150ORO_SCHED_RT

STSDetector

STSDetected

deployment/smSTSandWALK.osd


Robotics Software Frameworks ROS

Layout

Introduction

Robotics Software FrameworksRUPIDesign PatternOROCOSROS

Robotics Operating SystemFrameworks



Application



Definition

I ROS (Robot Operating System) provides libraries and tools to helpsoftware developers create robot applications. It provides hardwareabstraction, device drivers, libraries, visualizers, message-passing,package management, and more.

I Willow GarageI Created in 2006I 2008 first stable release of ROSI 2010 ROS 1.0



Connecting Middleware

I NodesI Server (roscore)I Output (rosout)

I TopicsI PublishersI Subscribers

I Parameterized ConnectionsI TCPI SharedMemoryI Serial (Arduino RosSerial) Figure: rxgraph of /Example node with its

topics



Meta-Operating System

I Meta-Operating-SystemI rosdepI rosmakeI roscdI rosedI rosrun

I Usefull toolsI rxgraphI rxplot

Figure: rxplot of /Example node with itstopics



excerpt Manifest

depth_reg

bonjean BSD

http ://ros.org/wiki/depth_reg


Robotics Software Frameworks Frameworks

Layout

Introduction

Robotics Software FrameworksRUPIDesign PatternOROCOSROSFrameworks

Conclusion



Application



Connectivity Question

I Exercice :I Description

I KinectI OpenCVI SLAMI Directions

I AimI When someone do hello then go to its direction



Example

I ExerciceI Description

I KinectI OpenCVI SLAMI Directions

I AimI When someone do hello then go to its direction

I ResultI Kinect -> OpenCV -> Position -> SLAM -> Directions



Connectivity Solutions

I In OROCOS :I Omni ORBI From Scratch Components Connection

I RPCI CORBAI Sockets -> Server/Client Approach

I ROS



Conclusion

I Overview ImplementationI Controller on one Computer : OROCOSI Communication between computing units : ROS

I MethodI Identify the states of your system (Tasks, loops)I Think of the time, delays and how to overlay some of themI Write the data flow for each stateI Look at the Computing Units At least one node per Unit (ROS)I Therefor the components are described (inside one node)


OS : Tasks And Threads Scheduling

Layout

Introduction


OS : Tasks And ThreadsScheduling

ModelAlgorithmsThread Scheduling

ManagementTime ServicesSynchronizationMessages and CommunicationIO Control


Application

Documentations



Scheduler

Aim : address any needs of a real-time software like emergency stop, highlevel action or reactivity needTaxonomy :

I Off-line/On-line algorithm : static/dynamic algorithmI Static/Dynamic prioritiesI pre-emptive/non pre-emptive algorithms :

I Ability to have mutual exclusion of a deviceI Scheduler cost lowI Small efficient



Scheduler

Properties that we look for :I Feasibility : ability to decide "a priori" that all the constraints will be

fulfilledI Predictability : response time of tasks is predictable.I Optimality : Optimal if able to find a schedule of every set of

feasibility tasksI Complexity : feasibility test is long and difficult?I Easiness to implement



Scheduler

Scheduler works only on active tasks :I Schedule Table : off-line schedulingI Off-line priorities definition, root of the schedulingI On-line analysis and scheduling



Analysis recipe

Scheduling problem :I To Model tasks of the system and their constraintsI To Choose a scheduling algorithmI To Validate feasibility on a set of tasks

I Theoretical feasibility : scheduling ability and complexityI Empirical feasibility : implement scheduler



Task model

Task families :I Linked task or not (Precedence constraint).I Important task or notI Repetitive or periodic task : activated regularlyI Non periodic task

I Sporadic : irregular activation but a minimum time between eachactivation

I Aperiodic : deadline is less strict and no minimum time between eachactivation



Task model

Parameters for task iI Si : start time when task arrives in the schedulerI Ci : Computation time needed by the task (Capacity).I Pi : PeriodI Di : Deadline of the taskI Ri : Earliest activation timeI Aperiodic task is defined by :

(Si ,Ci ,Di ,Ri )I Periodic task is defined by :

(Si ,Ci ,Di ,Pi )



Task model

Let’s consider a simplified model :I Periodic taskI Independent (No precedence constraint)I Starting time (worst case) : Si = 0I Deadline equal to Period : Pi = Di



Scheduler Structure

Computation of scheduling informationI On-line or Off-lineI Period, Deadline...

Waiting queue managementI One queue for each priorityI FIFO policyI Round Robin policy

Election phaseI Priority, deadline, ...



Rate Monotonic Algorithm

Off-line analysis, fixed priority, periodic tasks : Static softwareRationale

I Computation phase : priority = 1periodI Election phase : highest priority is chosen

PropertiesI Low ComplexityI Optimal Algorithm in fixed priority algorithm set



Rate Monotonic Algorithm

ExampleI Task 1 : C1 = 6, P1 = 10I Task 2 : C2 = 9, P1 = 30I Pre-emptive caseI Non pre-emptive case

Can be scheduled if load rate of the CPU U agrees with the followingsufficient condition :

U =n

∑i

CiTi≤ n× (2 1n − 1)



Critical time theorem

If every tasks both arrive at the same time in a system if they respect theirfirst deadline,thenevery other following deadlines will be respected whatever time they arrivein the system

I it’s a necessary and sufficient condition if every tasks arrive at thesame time

I else, it is a sufficient condition

If Di = Ti , finishing test is :

∀i , 1 ≤ i ≤ n min0≤t≤Dii

∑j=1

Cjt

⌈tTj

⌉≤ 1



Response time computation

Response time TR: Duration between time when a task begin and timewhen it is finished. Result can be exact relying on task model.

TRi = Ci + ∑j∈hp(i)

Ij

TRi = Ci + ∑j∈hp(i)

⌈TRiPj

⌉Cj

Where hp(i) represents a set of tasks with a higher priority than i .



Response time computation

Computation method : iterative way of evaluation

wn+1i = Ci + ∑j∈hp(i)

⌈wniPj

⌉Cj

I Let start with w0i = CiI Fail if wni > PiI Achieved if wn+1i = w

ni

Example : with P1 = 7, C1 = 3, P2 = 12, C2 = 2, P3 = 20, C3 = 5. Weassume that every task have the same priority and are ran in this order

TR1 = 3 TR2 = 5 TR3 = 18



Aperiodic tasks with high priorities

Periodic task dedicated to these tasks.

I bring feasibility in the worst caseI dedicated task is not activated if there is no aperiodic task to computeI easy solution, but sometime we loose some CPU load



Earliest Deadline First EDF algorithm

I Periodic task and aperiodicI On-line Algorithm, more useful than Rate Monotonic

Rationale :I Computation phase : Deadline computation

With priorityi (t) current priority at t and i the task :I Aperiodic task : priorityi (t) = Si +Di − tI Periodic task : priorityi (t) = Si (t) [last start activation time when

time is t] +Pi − tI Election phase: Earliest deadline is chosen.(Min)



EDF Example

Let consider 2 tasks :

T1 : C1 = 6, P1 = 10

T2 : C2 = 9, P2 = 30

I Pre-emptive caseI Non pre-emptive case



EDF Properties

Ability to schedule : Pre-emptive case, periodic and independent tasksI Necessary and sufficient condition if ∀i ,Di = Pi ; Only necessary if∃i ,Di ≤ Pi :

U =n

∑j=1

CjPj≤ 1

I Sufficient condition if ∃i ,Di ≤ Pi :

U =n

∑j=1

CjDj≤ 1



Server for aperiodic and sporadic jobs

I Periodic server :I Idle if waiting queue is emptyI Running in its time

0 5 10 15 20

PS

e1

e2

e1 e2




I Deferred server :I Time BudgetI Waiting for taskI Used to be in highest priority




I Sporadic server :I Like Deferred serverI But extra computation is done in background (lowest priority)



Services

Properties :I Threads and process capabilityI Fixed priorities, pre-emptive ⇒ RM easy. A minimum of 32 levels is a

mandatoryI One waiting queue for each priority and scheduling policy (SCHED_F

IFO, SCHED_RR, SCHED_OTHERS).I Available Services to specific users (like root)

Standard say that scheduling policies must be able to be applied each timethe choice threadprocess exists (ex. : choice of a threadprocess to release asemaphore).



Policies

POSIX.4 policies :#define SCHED_OTHER 0#define SCHED_FIFO 1#define SCHED_RR 2

I Parameter(s) : extensible to future policies

struct sched_param{int sched_priority;...

};

I Parameters modification:I Thread : creation of a thread from an attribute or modification of a

running thread.I Inherit from a fork() or modify of a running process.



API

sched_get_priority_max Get max priority value.sched_get_priority_min Get min priority value.sched_rr_get_interval Get duration of one time unit.sched_yield Free the CPU of this thread.sched_setscheduler Choose the scheduler policy.sched_getscheduler Get the scheduler policy value.sched_setparam Set parameters of the scheduler.sched_getparam Get parameters of the scheduler.pthread_setschedparam Set parameters of the scheduler for thread.pthread_getschedparam Get parameters of the scheduler for thread.

The last 2 function are working only on threads, other functions can beapplied on process/thread.



Example

struct sched_param parm;int res=-1;.../* Task T1 ; P1=10 */parm.sched_priority =15;res=sched_setscheduler(pid_T1 ,SCHED_FIFO ,&parm)if(res

OS : Tasks And Threads Management

Layout

Introduction


OS : Tasks And ThreadsSchedulingManagement

ProcessPosix Thread

Time ServicesSynchronizationMessages and CommunicationIO Control


Application

Documentations



Fork



Kill - Signal



POSIX Threads

Defined in chapter POSIX.4a (Portable Operating System Interface). Thischapter describe both threads and synchronization tools that are close tothreads (ex : mutex).Properties :

I A POSIX Thread is defined with a identifier that is local to theprocess.It owns its stack, its context and a set of attributes thatdescribe its behaviour.

I A POSIX Thread can be implemented in user space or in kernel space⇒ Standard describe only the interface not the way it is coded.



POSIX Threads

I Code must be re-entrant (or "thread safe") ⇒ code is able to becomputed in multiple instances in a safe way

I re-entrant code means :I don’t manipulate shared variables.I or it manipulate shared variables in a critical section (that mean no

other is able to access this variable when one is manipulating it) .

I Everything must be re-entrant user code but also system libraries (ex.libc.so)



POSIX threads

pthread_create Creation of a thread.Paramters : code, attributes, arg.

pthread_exit End of a thread.Parameter : return error value.

pthread_self returns id of the running threadpthread_cancel Destroy a thread.

Parameter : id of the thread.pthread_join Suspend a thread until

another is not finished.pthread_detach Suppress parent link

between threads.



POSIX Threads

pthread_kill Emit a signal to a thread.pthread_sigmask Modify signal mask of a thread.

In a POSIX.4a system, some services have a different semantic.I fork() : create a new process containing a thread where the main()

function is computedI exit() : finish a process and all threads it contains.



POSIX Threads

Creation and join example of a thread

#include void* th(void* arg){

printf ("I am thread %d ;process %d\n",pthread_self (),getpid ());pthread_exit(NULL);

}



POSIX Threads

Creation and join example of a thread


printf ("I am thread %d ;process %d\n",pthread_self (),getpid ());pthread_exit(NULL);

}



POSIX Threads

int main(int argc , char* argv []){

pthread_t id1 ,id2;pthread_create (&id1 ,NULL ,th,NULL);pthread_create (&id2 ,NULL ,th,NULL);pthread_join(id1 ,NULL);pthread_join(id2 ,NULL);printf ("End of main thread %d ;process %d\n",pthread_self (),getpid ());pthread_exit(NULL);

}



POSIX Threads

I With Solaris :

gcc -D_REENTRANT create.c -lpthread -lrt>a.out

I am thread 4 ; process 5539I am thread 5 ; process 5539End of main thread 1 ; process 5539

I With Linux :

gcc -D_REENTRANT create.c -lpthread>a.out

I am thread 1026 ; process 1253I am thread 2051 ; process 1254End of main thread 1024 ; process 1251



Thread Attributes

Thread Attributes : properties of a thread that are defined during itscreation. No heritage between father and son threads.

Example of attributes :Attribute Name Meaningdetachstate pthread_join possible or notpolicy scheduler policypriority level of priority of the thread (≥ 0)stacksize Size of the allocated stack



Thread Attributes

During creation of a thread, an structure of type pthread_attr_t can befilled and given if we want to specify none default attributes to the newthread :

pthread_attr_init Creation of a default attribute structure.pthread_attr_delete Destruction of attribute structure.pthread_attr_setATT set the value of "ATT" attribute.pthread_attr_getATT set the value of "ATT" attribute.

where ATT is replace by the name of the attribute.



Thread Attributes


printf ("I am thread %d \n",pthread_self ());

}



Thread Attributes

int main(int argc , char* argv []){

int i;pthread_t id;pthread_attr_t attr;struct sched_param param;pthread_attr_init (&attr);pthread_attr_setdetachstate (&attr ,PTHREAD_CREATE_DETACHED );pthread_attr_setschedpolicy (&attr ,SCHED_FIFO );param.sched_priority =1;pthread_attr_setschedparam (&attr ,& param);for(i=1;i


Thread Attributes

The TSD (Thread Specific Data area) : is an area of memory where arestored specific information of each thread.

Allow extension of regular attributes.pthread_key_create Creation of a key.pthread_key_delete Destruction of the key.pthread_getspecific get pointer value linked

to the key of the running thread.pthread_setspecific set pointer value linked

to the key of the running thread.



Thread Attributes

Creation of a new attribute :

pthread_key_t cd_key;

int pthread_cd_init(void){return pthread_key_create (&cd_key ,NULL);}

char* pthread_get_cd(void){return (char*) pthread_getspecific(cd_key );}



Thread Attributes

int pthread_set_cd(char* cd){

char* mycd = (char*) malloc(sizeof(char )*100);strcpy(mycd ,cd);return pthread_setspecific(cd_key ,mycd);

}int main(int argc , char* argv []){

pthread_cd_init ();pthread_set_cd ("/ here/dir ");printf ("My local directory is %s\n",pthread_get_cd ());

}


OS : Tasks And Threads Time Services

Layout

Introduction


OS : Tasks And ThreadsSchedulingManagementTime Services

Posix TimeXenomai Time services

SynchronizationMessages and CommunicationIO Control


Application

Documentations



Time manipulation

Time linked services :I What time is it ?I Block a thread/process during a defined time.I Wake up a thread/process regularly (timer) ⇒ periodic tasks.

Precision of these services :I Linked to what hardware we have (clock circuit), its features

(interruption period) and also to the software that use it (interruptionhandler).

I Ex : Linux Intel : circuit activated periodically (10 ms) ⇒ wakingbetween 10 to 12 ms.



Time Manipulation : POSIX Extensions

I Many timers are available ⇒ many physical clocks, profiling.I Need at least one real-time clock : CLOCK_REALTIME (less than 20

ms precise).I timespec structure ⇒ "theoretical" precision close to micro-seconds

....I Available services :I Get and set clocks.I Put a task in sleep mode.I Link periodic timer to UNIX signals ; and maybe with real-time

signals. With or without automatic restart.



Time Manipulation

clock_gettime Get clock value.clock_settime Set clock value.clock_getres Get clock resolution.timer_create Create a timer.timer_delete Remove a timer.timer_getoverrrun Give the number of unprocessed signalstimer_settime Activate a timer.timer_gettime Get time to the end of the timernanosleep Block a process/thread during a

defined duration.



Time Manipulation : Example

int main(int argc , char * argv []){timer_t monTimer; struct sigaction sig;struct itimerspec ti;timer_create(CLOCK_REALTIME ,NULL ,& monTimer );sig.sa_flags=SA_RESTART;sig.sa_handler=trop_tard;sigemptyset (&sig.sa_mask );sigaction(SIGALRM ,&sig ,NULL);ti.it_value.tv_sec=capacite;ti.it_value.tv_nsec =0;ti.it_interval.tv_sec =0; // here timer is notti.it_interval.tv_nsec =0; // automatically restartedtimer_settime(monTimer ,0,&ti ,NULL);



Time Manipulation : Example

printf ("Begin\n");while(go >0)

printf ("I am working .....\n");printf (" Unblocked by timer : deadline missed ..\n");

}

int go=1;void too_late(int sig){

printf (" Signal %d received\n",sig);go=0;

}

Execution :

BeginI am working .....I am working .....I am working .....

I am working .....I am working .....Signal 14 receivedUnblocked by timer : deadline missed ..



API Timer Management System

API :I void rt_timer_spin (RTIME ns) : busy clockI int rt_timer_set_mode (RTIME nstick) : TM_ONESHOT or

period timeHardware level :

I oneshotI periodic


OS : Tasks And Threads Synchronization

Layout

Introduction


OS : Tasks And ThreadsSchedulingManagementTime ServicesSynchronization

MutexVariable ConditionnalCounting SemaphoreXenomai Native API Synchronisation tools

Messages and CommunicationIO Control


Application

Documentations



Mutex

I Optimized Semaphores to implement critical section.I Waiting queue manager : depends of scheduling policy

(SCHED_FIFO, SCHED_OTHER, ...). Default behaviour : threadsare waked in decreasing order of priority

I Behaviour is defined by a set of attributes, main parameters are :Attribute name Meaningprotocol Inheriting Protocol usedpshared Inter-process or inter-thread mutexceiling Priority ceiling



Rationale

Programming mechanism that can block a thread while a condition is nottrue.

I Solution is based on a mutex and a Var CondI Waking signal has no memory : if nothing is waiting for the condition,

waking signal is lost ( 6= counting semaphores).I Waiting queue management : depend on scheduling policy

(SCHED_FIFO, SCHED_OTHER, etc ...). Default behaviour :threads are waked in decreasing order of priority.



Mutex

pthread_mutex_init Initialize a mutex.pthread_mutex_lock Lock the mutex in blocking manner eventually.pthread_mutex_trylock Non blocking try to lock the mutexpthread_mutex_unlock Release the mutex lock.pthread_mutex_destroy Destruct the mutex.pthread_mutexattr_init Initialize an attribute structurepthread_mutexattr_setATT Set attribute ATT.pthread_mutexattr_getATT Get attribute ATT value.

o ATT is one of the attributes of the mutex.



API

pthread_cond_init Initialize a variable.pthread_cond_destroy Destruct a variable.pthread_cond_wait Wait a waking signal coming from a condition.pthread_cond_signal Signal that a condition is true to one threadpthread_cond_broadcast Signal that a condition is true to all threads



Mechanism

A classical program where a thread modify a variable : a mutex is used(var_mutex) and a condition is used (var_cond).

pthread_mutex_lock (& var_mutex );/* Modify the variable in criticalsection */var = .... ;

/* If the condition is fulfilled , wealert the blocked thread */if(condition(var))

pthread_cond_signal (& var_cond );

pthread_mutex_unlock (& var_mutex );



Mechanism

Classical program that wait for a variable to be modified :

pthread_mutex_lock (& var_mutex );while(! condition(var)){

/* If the condition is not true ,wait */

pthread_cond_wait (&var_cond , &var_mutex );}/* use the variable in critical section */.....

pthread_mutex_unlock (& var_mutex );

Attention pthread_cond_wait is making some implicit lock and unlock ofthe mutex.



Example

int y=2, x=0;pthread_mutex_t mut;pthread_cond_t cond;void* th(void* arg){

int cont =1;while(cont){

pthread_mutex_lock (&mut);x++;printf ("x++\n");if (x > y){

pthread_cond_signal (&cond);cont =0; }

pthread_mutex_unlock (&mut );}}



Example

int main(int argc , char* argv){pthread_t id;pthread_mutex_init (&mut ,NULL);pthread_cond_init (&cond ,NULL);pthread_mutex_lock (&mut);pthread_create (&id ,NULL ,th,NULL);while (x y is true



Counting semaphore

I Semaphore: waiting queue + counter.I No management of priority inversion : case must be treated in

developer level.I Used for synchronization and inter-process or inter-thread mutual

exclusion.I Waiting queue management : depend on scheduling policy

(SCHED_FIFO, SCHED_OTHER, etc ...). Default behaviour :threads are waked in decreasing order of priority.

I Two kind of semaphore : named and unnamed semaphore.



Counting Semaphore

sem_open Connection to a named semaphore.sem_close Disconnection to a named semaphore.sem_unlink Destruction of a named semaphore.sem_init Initialisation of a unnamed semaphore..sem_destroy Destruction of a unnamed semaphore.sem_post Freeing a semaphore.sem_wait Acquiring a semaphore.sem_trywait Non blocking acquiring of a semaphore.



Counting Semaphore Example

#include #include sem_t sem;int main(int argc , char* argv []){

pthread_t id;struct timespec delay;sem_init (&sem ,0,0);pthread_create (&id ,NULL ,th,NULL);deli.tv_sec =4; deli.tv_nsec =0;nanosleep (&delay ,NULL);printf ("main thread %d : free from

the other thread \n",pthread_self ());sem_post (&sem);pthread_exit(NULL);

}



Counting Semaphore Example

void* th(void* arg){

printf (" thread %d waiting\n",pthread_self ());sem_wait (&sem);printf (" thread %d unblocked \n",pthread_self ());

}

Execution

thread 4 waitingmain thread 1 : free fromthe other threadthread 4 unblocked



API Mutexes

int rt_mutex_create (RT_MUTEX *mutex, const char *name)int rt_mutex_acquire (RT_MUTEX *mutex, RTIME timeout)int rt_mutex_release (RT_MUTEX *mutex)



API Condition variables

int rt_cond_create (RT_COND *cond, const char *name)int rt_cond_signal (RT_COND *cond)int rt_cond_broadcast (RT_COND *cond)int rt_cond_wait (RT_COND *cond, RT_MUTEX *mutex, RTIME timeout)



API Counting Semaphores

int rt_sem_create (RT_SEM *sem, const char *name,unsigned long icount, int mode)

int rt_sem_p (RT_SEM *sem, RTIME timeout)int rt_sem_v (RT_SEM *sem)int rt_sem_broadcast (RT_SEM *sem)


OS : Tasks And Threads Messages and Communication

Layout

Introduction


OS : Tasks And ThreadsSchedulingManagementTime ServicesSynchronizationMessages and Communication

SignalsMail QueueXenomai Native API

IO Control


Application

Documentations



Real-Time Signals

Signal : event delivered in asynchronous way to a process/thread (softwareinterruption).

I Blocked signals (or masked) pending or delivered.I Default behaviour can be modified by user.I One signal register for each thread/process.



Real-Time Signals

Existing mechanism in POSIX.1 but with the following issues :I Implementation pending signal register = unsafe delivery (possible

loss).I Emitting order not respected when they are delivered.I Does not contain many information and few of them are available for

user : not adapted to IPC implementation.I Not efficient (slow : high latency).



Real-Time Signals : POSIX Interface

kill Emission of a signal.sigaction Connection of a handler to a signal.sigemptyset Initialize with all signals disabled.(mask all signals)sigfillset Initialize with all signals enabled.(unmask all signals)sigaddset Add a signal in the set(unmask this signal).sigdelset Remove a signal from the set(mask this signal).sigismember Check if the signal is enabled in the set.sigsuspend Block a process until a signal is received.sigprocmask Install a mask.



Signals : Non RT Example

void handler(int sig){printf (" Signal %d received\n",sig);}

int main(int argc , char * argv []){struct sigaction sig;sig.sa_flags=SA_RESTART;sig.sa_handler=handler;sigemptyset (&sig.sa_mask );sigaction(SIGUSR1 ,&sig ,NULL);while (1); // program computes !!

}

Execution :$sig &$kill -USR1 14090Signal 10 received



Real-Time signals : POSIX Extended

Range of new signals numbered from SIGRTMIN to SIGRTMAX (thatrepresent a minimum of RTSIG_MAX signals)

I Possibility to use a value linked to this signal.I No loss of signal : using of a queue for pending signals.I Ordered delivery : respecting scheduling policy chosen + priority

linked to a signal ⇒ SIGRTMIN has the highest priority.I Emitted with a kill, sigqueue, with a timer or by an asynchronous IO.



Real-Time Signals : POSIX Extended

Complementary interfaces of POSIX.4 :sigqueue Emit a real-time signal.sigwaitinfo Wait for a signal without handler executionsigtimedwait Idem above + timeout on blocking time.



Real-Time Signals : RT Example

int main(int argc , char * argv []){struct sigaction sig;union sigval val;int cpt;sig.sa_flags=SA_SIGINFO;sig.sa_sigaction=handler;sigemptyset (&sig.sa_mask );if(sigaction(SIGRTMIN ,&sig ,NULL)


RealTime Signals : RT Example

void handler (int sig , siginfo_t *sip , void *uap){

printf (" Received signal %d, val = %d \n",sig ,sip ->si_value.sival_int );

}

Execution :

\$rt -sigReceived signal 38, val = 0Received signal 38, val = 1Received signal 38, val = 2Received signal 38, val = 3Received signal 38, val = 4



Mechanism

With UNIX, Communication mechanism is the pipeline (named or not) ⇒too abstract for real-time constraints.

Mail queues in POSIX.4 have the same features :I Priority in emission/reception.I Can work in Non-blockingI Can preallocate resources.I Can communicate in Inter-Process and Inter-Thread mode.I Unfortunately, priority inversion issues are not addressed.



API

mq_open Creation or connection to a queue.mq_unlink Destruction of a queue.mq_receive Reception of the oldest and the most important

mail.mq_send Emission of a mail with a given prioritymq_close Disconnection to a queue.mq_notify Notification that there is a new mail.mq_setattr Set attributes of the queue.mq_getattr Get attributes of the queue.



Example

/* Emission with a priority 1 (from 0 toMQ_PRIO_MAX) */

mq_send(id,buff ,100 ,1);pthread_create (&tid ,NULL ,consumer ,NULL);pthread_exit(NULL);

}

void* consumer(void* arg){mqd_t id;char buff [100];id=mq_open ("/ myqueue",O_RDONLY );mq_receive(id,buff ,100, NULL);printf ("msg = %s\n",buff);mq_unlink ("/ myqueue ");pthread_exit(NULL);

}



Example

#include #include int main(int argc , char* argv []){

pthread_t tid;mqd_t id;char buff [100];struct mq_attr attr;attr.mq_maxmsg =100;attr.mq_flags =0;attr.mq_msgsize =100;id=mq_open ("/ mafile",O_CREAT|O_WRONLY ,

444,& attr);strcpy(buff ,"Hi !!");...

}



API Event flags groups

I Synchronizing object based on a long word structure.I Any bit in the word can be used as a user flagI Task oriented signal mechanismI Conjunctive or Disjunctive



API Event flags groups

int rt_event_create (RT_EVENT *event, const char *name,unsigned long ivalue, int mode)

int rt_event_signal (RT_EVENT *event, unsigned long mask)int rt_event_wait (RT_EVENT *event, unsigned long mask,

unsigned long *mask_r, int mode, RTIME timeout)int rt_event_clear (RT_EVENT *event, unsigned long mask,

unsigned long *mask_r)



API Messages queue

int rt_queue_create (RT_QUEUE *q, const char *name,size_t poolsize, size_t qlimit, int mode)

void * rt_queue_alloc (RT_QUEUE *q, size_t size)int rt_queue_free (RT_QUEUE *q, void *buf)int rt_queue_send (RT_QUEUE *q, void *mbuf, size_t size, int mode)int rt_queue_write (RT_QUEUE *q, const void *buf, size_t size, int mode)ssize_t rt_queue_receive (RT_QUEUE *q, void **bufp, RTIME timeout)ssize_t rt_queue_read (RT_QUEUE *q, void *buf, size_t size, RTIME timeout)



API Messages pipe

int rt_pipe_create (RT_PIPE *pipe, const char *name,int minor, size_t poolsize)

ssize_t rt_pipe_receive (RT_PIPE *pipe,RT_PIPE_MSG **msgp, RTIME timeout)

ssize_t rt_pipe_read (RT_PIPE *pipe, void *buf, size_t size, RTIME timeout)ssize_t rt_pipe_send (RT_PIPE *pipe, RT_PIPE_MSG *msg,

size_t size, int mode)ssize_t rt_pipe_write (RT_PIPE *pipe, const void *buf, size_t size,

int mode)ssize_t rt_pipe_stream (RT_PIPE *pipe, const void *buf, size_t size)RT_PIPE_MSG * rt_pipe_alloc (RT_PIPE *pipe, size_t size)int rt_pipe_free (RT_PIPE *pipe, RT_PIPE_MSG *msg)int rt_pipe_flush (RT_PIPE *pipe, int mode)



Example : Pipe Kernel side

#include #include #include #include #include #define TASK_PRIO 0 /* Highest RT priority */#define TASK_MODE T_FPU|T_CPU (0) /* Uses FPU , bound to CPU #0 */#define TASK_STKSZ 4096 /* Stack size (in bytes) */

RT_TASK task_desc;RT_PIPE pipe_desc;

void task_body(void){RT_PIPE_MSG *msgout , *msgin;int err , len , n;for (;;) {/* ... */len = sizeof (" Hello ");/* Get a message block of the right size in order toinitiate the message -oriented dialog with theuser -space process. */msgout = rt_pipe_alloc(len);if (! msgout)fail ();



Example : Pipe Kernel side

#include RT_PIPE pipe_desc;int init_module (void){int err;/* Connect the kernel -side of the message pipe to thespecial device file /dev/rtp7. */err = rt_pipe_create (&pipe_desc ," MyPipe",7,NULL);...}



Example : Pipe User side

From a regular Linux process:#include int pipe_fd;int main (int argc , char *argv []){/* Open the Linux side of the pipe. */pipe_fd = open ("/ dev/rtp7",O_RDWR );/* ou grace au service de registres */pipe_fd = open ("/ proc/xenomai/registry/native/pipes/MyPipe",O_RDWR );.../* Write a message to the pipe. */write(pipe_fd ,"hello world ",11);...}


OS : Tasks And Threads IO Control

Layout

Introduction


OS : Tasks And ThreadsSchedulingManagementTime ServicesSynchronizationMessages and CommunicationIO Control

MemoryIO


Application

Documentations



Memory Management

A shared time system leads to possible time indeterminism because :I Dynamic memory allocation.I Page swap : swapin=swapout.

Solution : limit dynamic memory allocation and lock pages in centralmemory (POSIX.4 Interface) :

I mlockall()=munlockall() : lock/unlock swap with all memory pages ofthis process..

I mlock()=munlock() : lock/unlock a range of addresses.

! Warning : mlock() is not portable (because there is no memory model inPOSIX standard).



API Memory heap

int rt_heap_create (RT_HEAP *heap, const char *name, size_t heapsize, int mode)int rt_heap_alloc (RT_HEAP *heap, size_t size, RTIME timeout, void **blockp)int rt_heap_free (RT_HEAP *heap, void *block)



Posix AIO

I aio_readI aio_writeI aio_return, aio_errorI aio_cancelI aio_fsyncI aio_suspend



Example :

sa.sa_sigaction = aioSigHandler;if (sigaction(

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