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Automotive embedded systems part4 v1
- 1. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system AutomotiveEmbedded Systems part4 (OSEK OS). ENG.KEROLES SHENOUDA 1
- 2. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system OSEK/VDX OperatingSystem it's time to wake up Learn In Depth 2
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- 4. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system In order to allow OSEK-OS to be used in a variety of systems with different capacities and demands (for example memory, processing capacity, etc.) is that OSEK-OS defines 4 classes of compliance (CC). Conformance classes are determined according to the following attributes: Multiple activation of basic tasks Types of tasks accepted: basic and extended Number of tasks by priority 4
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- 6. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system HookRoutines The hookroutines are functions implemented by the user that the operating system will call in specific situations. They are optional and can be used to add some specific management desired by the user in the following situations: StartupHook: it is called during the initialization of the operating system, before being completed. ShutdownHook: it is called at the end of the shutdown of the operating system. PreTaskHook: is called before proceeding to execute a task. • PostTaskHook: is called when the execution of a task ends. ErrorHook: it is called in case any of the interfaces of the operating system returns a value other than E_OK. 6
- 7. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system HookRoutines Features OSEK proposes dedicated routines (or functions) to allow the user to «hook » an action at important stages in system calls. “hook routines” are/have: called by the operating system; a priority greater than all tasks; not interrupted by ISR2 (presented after); a standardized interface; able to call a subset of the operating system services. 7
- 8. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system StartupHook 8 iscalled after the startup of the OS but before the startup of the scheduler
- 9. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system StartupHookexample 1.After completing the initialization of C, the main function is called, the same in this case proceeds to start the execution of the operating system in 2. 3 Once the initialization of the operating system, the same calls StartupHook. 4 Just when you start StartupHook starts the Scheduler and it proceeds to run Tasks 9 1.For the operating system to call the StartupHook, the same should be indicate by setting STARTUPHOOK to TRUE 2 Just after calling Startup- Hook the operating system will proceed to start the Scheduler, so the task InitTask will be executed after StartupHook
- 10. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system PreTaskHookand PostTaskHook PreTaskHook and PostTaskHook PreTaskHook is called just before a task goes from READY state to RUNNING state; PostTaskHook is called just before a task goes from RUNNING state to READY or SUSPENDED state; 10
- 11. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system PreTaskHookexample 11 For the operating system to call the PreTaskHook, the same should be indicated configuring the PRETASKPHOOK parameter TRUE.
- 12. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system PostTaskHookexample 12 For the operating system to call the PreTaskHook, the same should be indicated configuring the POSTTASKPHOOK parameter TRUE.
- 13. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system ErrorHook This routine called when a system call does not return E_OK, that is if an error occurs during a system call. 13
- 14. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system ErrorHook 14 Forthe operating system to call the ErrorHook, the same should be indicated configuring the ERRORHOOK parameter TRUE
- 15. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_systemExampleof centralised error handling (extended status) The macro OSErrorGetServiceId() provides the service identifier where the error has been risen. the macros to access the parameters of SetRelAlarm are: OSError_SetRelAlarm_AlarmID() OSError_SetRelAlarm_increment() OSError_SetRelAlarm_cycle() 15
- 16. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system ShutdownHook 16 1In case an error has not occurred, Error parameter will have the value E_OK. 2 ShutdownHook is called from ShutdownOS, therefore it is necessary to turn off the system so that it is called. For the operating system to call the ShutdownHook, the same should be indicated configuring the SHUTDOWNHOOK parameter TRUE.
- 17. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system levelsof error OSEK-OS offers two levels of error checking that can be configured in the .oil file extended: it is the mode used during development. Some extra checks are made and returned in case of error. standard: this is the mode used in production. Only very critical errors are detected and reported. In this Example, "Error handling" is used the ActivateTask interface that can return E_OK, E_OS_LIMIT or E_OS_ID when the level of the error check is set to extended but only E_OK and E_OS_LIMIT when the level of error checks It is established to standard. 17
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- 19. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system SharedData between Tasks 19 how does the consumer know that (new) data is available? Data is shared between several tasks and, in order to keep the data in a consistent state, we need to protect it from concurrent access. In other words: access to the data must be serialized. This use case is mainly about task synchronization: the interplay between producer and consumer must work smoothly. How does a consumer know that new data is available? how to serialize access to shared data?
- 20. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Twoshared Resource Control 20 the mutex = MUTual EXclusion. the semaphore Resource A resource is any entity used by a task. A resource can thus be an I/O device such as a printer, a keyboard, a display, etc. or a variable, a structure, an array, etc. Shared Resource A shared resource is a resource that can be used by more than one task. Each task should gain exclusive access to the shared resource to prevent data corruption. This is called Mutual Exclusion.
- 21. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system themutex A critical section is a piece of code (part of a function) from which the access to the shared resource must be atomic. At a certain moment in time, one and only one critical section is allowed to access the shared data The mutex implements two operations: acquire: enter the critical section, or sleep if another task has already acquired the mutex, and release: leave the critical section. Other tasks now have the possibility to acquire the mutex. 21
- 22. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system themutex The concept of ownership is very important here: the task that acquired the mutex must release it as well. techniques to address mutual exclusion include: disabling/enabling interrupts disabling scheduling performing test-and-set operations (indivisibly) using semaphores 22
- 23. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system MutualExclusion Disable interrupts Mechanism Demand: exclusive use of a resource Disable interrupts Used on critical sections of code disabling/enabling interrupts used to access a few variables or small data structures used when the process time is minimal affects interrupt latency you should not disable interrupts for any longer than the kernel does in C/OS-II: OS_ENTER_CRITICAL( ); … // you can access shared data here OS_EXIT_CRITICAL( ): 23
- 24. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system MutualExclusion Disable interrupts Mechanism 24 So if a shared resource is shared between a task and an interrupt service routine, then the task can disable interrupts before entering the shared resource. This will stop the ISR from accessing the shared resource Disadvantages: 1. Disabling interrupt for long time harm the system response And the RTOS Kernel Itself
- 25. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_systemMutualExclusion Disable preemption (Task Switching) Mechanism 25 disabling scheduling instead of disabling all maskable interrupts, you may just want to disable the scheduler an interrupted task is returned to, not necessarily the highest priority task implies that data is not shared with the ISRs in C/OS-II: OSSchedLock( ); … // you can access shared data here OSSchedUnlock( );
- 26. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system performingtest-and-set operations (indivisibly) perform test-and-set operations (indivisibly) two tasks may agree that to use a common resource, they must first check a global variable while it is being checked, and before it is set, by one task, it must be made inaccessible by the other this can be achieved by: disabling interrupts (above) or some processors now support a single TAS instruction Make the following test test-and-set variable Set test-and-set variable to 1 Access resource Set test-and-set variable to 0 26 Kindly Note: DPRAM test-and-set instructions can work in many ways When CPU 1 issues a test-and-set instruction, the DPRAM first makes an "internal note" of this by storing the address of the memory location in a special place. If at this point, CPU 2 happens to issue a test- and-set instruction for the same memory location, the DPRAM first checks its "internal note", recognizes the situation, and issues a BUSY interrupt, which tells CPU 2 that it must wait and retry.
- 27. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system SEMAPHORES| Operating System (Simplified) 27 https://www.youtube.com/watch?v=PQ5aK5wLCQE
- 28. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system MutualExclusion - semaphores a protocol mechanism to control access to shared resources, signal the occurrence of an event or allow two tasks to synchronize one analogy is that in order for a task to use a resource it must first draw a key for it if the key(s) is in use, the task suspends wait on (pend) & signal (post) semaphore two types of semaphores: binary and counting (general) 28 task 2 task 1 1. pend 4. post Printer 2. pend 6. post 5. “my name is task 2” 3. “my name is task 1”
- 29. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system MutualExclusion - semaphores 29 accessing shared data in C/OS-II OS_EVENT *SharedDataSem; SharedDataSem = OSSemCreate(1); ... void Function (void) { INT8U err; //read as “char *err” (string) ... OSSemPend(SharedDataSem, 0, &err); … //access shared data OSSemPost(SharedDataSem); } binary semaphore timeout value {wait forever in this case} error message code
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- 32. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Accessingshared resources Hardware and software resources may be shared between tasks (an optionally between tasks and ISR2 in OSEK). Resource management ensures that two tasks cannot occupy the same resource at the same time. priority inversion can not occur. deadlocks do not occur by use of these resources. two tasks or interrupt routines cannot occupy the same resource at the same time. 32
- 33. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Exampleof an unprotected software resource (global variable): 33 val may contain 2 … or 1 non determinism
- 34. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Resources If two applications simultaneously use a resource such as being a data bus or a port but they do not synchronize with each other, the result can be indeterminate. For this reason, in order to access resources, conventional traffic lights are used or mutex to be able to access them from several tasks without generating interference or collisions between them. However, the use of traffic lights and mutex have two problems: inversion of priorities: occurs when a relatively high priority task must be blocked by requiring the use of a resource that is being used by a priority task minor that was interrupted to execute the highest priority task. deadlocks: occurs when two tasks use two resources (or semaphores) in reverse order blocking each other. OSEK-OS offers a solution for accessing resources that avoids both these problems. 34
- 35. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Priorityinversion on occupying semaphores This means that a lower-priority task delays the execution of higher-priority task. sequencing of the common access of two tasks to a semaphore (in a full preemptive system, task T1 has the highest priority) Task T4 which has a low priority, occupies the semaphore S1. T1 preempts T4 and requests the same semaphore. As the semaphore S1 is already occupied, T1 enters the waiting state. Now the low-priority T4 is interrupted and preempted by tasks with a priority between those of T1 and T4. T1 can only be executed after all lower-priority tasks have been terminated, and the semaphore S1 has been released again. Although T2 and T3 do not use semaphore S1, they delay T1 with their runtime. 35
- 36. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_systemDeadlocksituation using semaphores In this case deadlock means the impossibility of task execution due to infinite waiting for mutually locked resources The following scenario results in a deadlock: Task T1 occupies the semaphore S1 and subsequently cannot continue running, e.g. because it is waiting for an event. Thus, the lower-priority task T2 is transferred into the running state. It occupies the semaphore S2. If T1 gets ready again and tries to occupy semaphore S2, it enters the waiting state again. If now T2 tries to occupy semaphore S1, this results in a deadlock 36
- 37. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system OSEKPriority Ceiling Protocol To avoid the problems of priority inversion and deadlocks the OSEK operating system requires following behavior: At the system generation, to each resource its own ceiling priority is statically assigned. The ceiling priority shall be set at least to the highest priority of all tasks that access a resource or any of the resources linked to this resource If a task requires a resource, and its current priority is lower than the ceiling priority of the resource, the priority of the task is raised to the ceiling priority of the resource. If the task releases the resource, the priority of this task is reset to the priority which was dynamically assigned before requiring that resource. 37
- 38. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system OSEKPriority Ceiling Protocol (PCP) the mechanism of the priority ceiling. Task T0 has the highest, and task T4 the lowest priority. Task T1 and task T4 want to access the same resource. The system shows clearly that no unbounded priority inversion is entailed. The high-priority task T1 waits for a shorter time than the maximum duration of resource occupation by T4. 38
- 39. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Resourceassignment with priority ceiling between preemptable tasks and interrupt services routines. To determine the ceiling priority of resources which are used in interrupts, virtual priorities higher than all tasks priorities are assigned to interrupts 39
- 40. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Resourceassignment with priority ceiling between interrupt services routines 40
- 41. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system OSEKresources OSEK resources are used to do mutual exclusion between several tasks (or ISR2) to protect the access to a shared hardware or software entity. Example of hardware entity: LCD display; Communication network (CAN, ethernet, … ). Example of software entity: a global variable; the scheduler (in this case, the task may not be preempted). 41
- 42. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system OSEKresources Cont. OSEK/VDX offers a RESOURCE mechanism with 2 associated system calls: GetResource ReleaseResource 42
- 43. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system GetResource StatusType GetResource ( ResourceType <ResID> ) ; Get the resource ResID; StatusType is an error code: E_OK: no error; E_OS_ID: the resource id is invalid; E_OS_ACCESS: trying to get a resource that is already in use (it is a design error). A task that « own » the resource may not be preempted by another task that will try to get the resource. 43
- 44. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system ReleaseResource StatusType ReleaseResource ( ResourceType <ResID> ) ; Release the resource ResID; StatusType is an error code: E_OK: no error; E_OS_ID: the resource id is invalid; E_OS_ACCESS: trying to release a resource that is not in use (it is a design error). 44
- 45. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Tasksgroup This feature allow to mix non-preemptable tasks and preemptable tasks. In the same group all the tasks are seen as non-preemptable by the other tasks of the group. A task having a higher priority of all the tasks of the group (and not part of the group) may preempt any task of the group. This feature uses an internal resource for each group: The internal resource is got automatically when the task start to run; The internal resource is released automatically when the task terminates; An internal resource may not be reference with GetResource() or ReleaseResource(). 45
- 46. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system OILDescription of a resource RESOURCE resA { RESOURCEPROPERTY = STANDARD; }; 46 TASK myTask { PRIORITY = 2; AUTOSTART = FALSE; ACTIVATION = 1; SCHEDULE = NON; RESOURCE = resA; STACKSIZE = 32768; };
- 47. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Lab6:Resources (expect what the output and draw the task timeline) LEARN IN DEPTH 47
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- 53. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Lab6:Resources (expect what the output and draw the task timeline) LEARN IN DEPTH 53
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- 60. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system “RES_SCHEDULER”Resource There is a resource that is always available for tasks and is the RES_SCHEDULER. By using this resource a PREEMPTIVE task can block any other while it is performing an action during which does not want to be interrupted. In this way it is possible for a PREEMPTIVE task transforming itself during the use of this resource into a NON PREEMPTIVE task. 60
- 61. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system UsingRES_SCHEDULER "Using RES_SCHEDULER" you can see that the DemoTask task has been configured as PREEMPTIVE, and therefore You can use the resource RES_SCHEDULER. The use of the RES_SHEDULER resource from a NON PREEMPTIVE task has no meaning, it will not be interrupted by itself by no other, regardless of whether or not it uses the resource RES_SCHEDULER. 61
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- 63. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system InternalResources OSEK-OS offers the possibility of defining internal resources. These resources are not handled and released by using GetResource and ReleaseResource but they are automatically reserved and released by the system at Begin and finish a task. By using internal resources the user is allowed to create task groups cooperatives which use the same internal resource. In this way all the tasks that use the same internal resource behave each other as NON PREEMPTIVE. 63
- 64. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system InternalResources Example As you can see "Using internal resources" the task DemoTask1 during its processing will never be interrupted by DemoTask3, despite of this having a priority of 5 and this is greater than the priority of DemoTask1 which is 1. Both DemoTask1 and DemoTask3 will have a priority of 5.5 when running "OSEK Priority Ceiling Protocol"). However, DemoTask1 may be interrupted by DemoTask2 that has a priority of 3, since it does not use the internal resource. DemoTask3 will be able to interrupt DemoTask1 if it calls Schedule when DemoTask3 is in the ready state. In this way it is possible to arm groups of tasks that do not interrupt each other, or interrupt only explicitly when the user calls Schedule. 64
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- 66. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Linkeados Resources Linking two resources is linked internally so that for the operating system They have different names but they are treated as if they were the same resource. In this Example, "Using Linked Resources" you can see two TaskA tasks and TaskB using respectively Res1 and Res2. The operating system treats both resources as if they were the same. 66
- 67. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system Prepareyour self for the next session (AUTOSAR OS) #LEARN_IN_DEPTH 67
- 68. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system References Embedded Microcomputer Systems Real Time Interfacing Third Edition Jonathan W. Valvano University of Texas at Austin. MicroC/OS-II the real-time kernel second edition jean j.labrosse. RTOS Concepts http://www.embeddedcraft.org. OSEK/VDX Operating System Specification 2.2.3 AUTOSAR Layered Software Architecture The Trampoline Handbook release 2.0 Trampoline (OSEK/VDX OS) Test Implementation -Version 1.0, Florent PAVIN ; Jean-Luc BECHENNEC 68
- 69. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system References Trampoline:an open platform for (small) embedded systems based on OSEK/VDX and AUTOSAR http://trampoline.rts-software.org/ Jean-Luc Béchennec1;2, Sébastien Faucou1;3 1IRCCyN (Institute of Research in Communications and Cybernetics of Nantes) 2CNRS (National Center for Scientific Research) / 3University of Nantes 10th Libre Software Meeting 69
- 70. https://www.facebook.com/groups/embedded.system.KS/ Follow us Press here #LEARN_IN DEPTH #Be_professional_in embedded_system References Real Time Systems (RETSY) Jean-Luc Béchennec - Jean-Luc.Bechennec@irccyn.ec-nantes.fr Sébastien Faucou - Sebastien.Faucou@univ-nantes.fr jeudi 12 novembre 15 AUTOSAR Specification of Operating System V5.0.0 R4.0 Rev 3 OSEK - Basics http://taisnotes.blogspot.com.eg/2016/07/osek-basic- task-vs-extended-task.html OSEK OS Session Speaker Deepak V. M.S Ramaiah School of Advanced Studies - Bangalore 1 Introducción a OSEK-OS - El Sistema Operativo del CIAA-Firmware Programación de Sistemas Embebidos MSc. Ing. Mariano Cerdeiro 70
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