VxWorks Interview Questions & Answers

  1. Question 1. What Is The Memory Layout In Vx Works?

    Answer :

    The memory layout in vxworks is known as flat physical address space,

    The diagram shows, how the memory is been divided in to different regions on target board RAM

    SysPhysMemTop()
    SysMemTop()
    FREE_RAM_ADDRESS
    RAM_LOW_ADDRESS
    LOCAL_MEM_LOCAL ADDRESS

  2. Question 2. What Is Difference Between Signals And Interrupts?

    Answer :

    Signals will tell about that some invent has occurred. But when an interrupt has occurred the system has to stop the current task and has to switch to ISR.

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  4. Question 3. How Vx Works Differ From Unix.?

    Answer :

    VxWorks runs in one mode. No protected vs. user mode switching is done. Running in supervisor mode on most processors, and not using traps for system calls.

    UNIX provides resource reclamation; by default, VxWorks does not.

    VxWorks does not have full “process”; it only has tasks, or “threads”.

  5. Question 4. What Is Priority Inversion?

    Answer :

    When task with lowest priority is executing the highest priority task has to wait till lowest priority task releases the resource.

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  7. Question 5. What Is Ipc (inter Process Communication) ?

    Answer :

    A technique used to communicate between two process executing on same processor or on different processor Any of this ipc can be used for communication, Message queue , Pipes, Shared memory.

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  9. Question 6. What Is Task Switching?

    Answer :

    When kernel finds highest priority task than the current running task then it will preempt the current running task and allocate memory for the highest priority task. Time taken to switch from one task context to another task context another task context is called task switching.

  10. Question 7. What Are Message Queues And Pipes?

    Answer :

    Message queues and pipes are a way of inter task communication used to send and receive message between two tasks.

    Pipes are virtual Io and unidirectional.messages are sent and received in form of bytes. Message queue can be created with variable length messages are sent by passing address of the buffer which holds the message . message queue created with queue length of one is called as mailbox , it can be used for synchronization.

    User reserved memory

    System memory pool

    WDB_POOL_SIZE

    Vxworks + application

    interrupt vector

    table,bootline, exception message

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  12. Question 8. Difference B/w Vxworks And Linux Os?

    Answer :

    VxWorks runs in one mode. No protected vs. user mode switching is done. Running in supervisor mode on most processors, and not using traps for system calls. linux provides resource reclamation; by default, VxWorks does not. VxWorks does not have full “process”; it only has tasks, or “threads”.

  13. Question 9. What R Scheduling Algorithms?

    Answer :

    There are 2 scheduling algorithms in Vxworks 

    1. Priority based preemptive scheduling algorithm(Vx works- default)
    2. round robin scheduling algorithm. (UNIX default)
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  15. Question 10. Advantages Of Vx Works And Why?

    Answer :

    Vxworks provides characteristics like Deterministic,Multitasking, Fast Context Switching, Support for Preemptive Based Scheduling Support for  Multiple Priority level,Support for Inter Task Communication, Support for Inter Task Synchronization, Low Interrupt Latency Low Memory Footprint, Scalable

    Which makes intertask communication faster and context switching latency is reduced because, all tasks resides in common address space,no swaping and paging of memory is used. Vxworks can be scaled, unnecessary components can be easily excluded.memory usage will be greatly reduced because of this feature.

    Vxworks is extendable, new components can be added like a task. 

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  17. Question 11. What Does Target Server Do?

    Answer :

    Target server provides host-based management of target resources needed by development tools:

    1. Communication with debug agent on target.
    2. Dynamic module loading and unloading.
    3. Host-resident symbol table for target.
    4. Allocation of memory on target for host tools.
    5. All Tornado tools use the Wind River Tool Exchange Protocol (WTX) to communicate with the target server. The WTX protocol is documented.
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  19. Question 12. What Is The Difference B/w Downloadable And Bootable Application?

    Answer :

    Bootable Project – A project used to configure and build VxWorks images for a particular BSP. Application code may be statically linked to such a VxWorks image, and the application’s start-up code may be specified.

    Downloadable Project – A project used to manage and build application modules which can be downloaded and dynamically linked with a running VxWorks image. Allows “on the fly” development.

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  21. Question 13. What Is Tornado And Its Features?

    Answer :

    1. Integrated development environment For vxworks 5.4 , tornado used is 2.0. 
    2. An integrated source-code editor.
    3. A project management facility.
    4. Integrated C and C++ compilers and make.
    5. The browser, Collection of visualization aids to monitor the target system.
    6. CrossWind, Graphically enhanced source-level debugger.
    7. WindSh, C-language command shell that controls the target.
    8. An integrated version of the VxWorks target simulator, VxSim.
    9. An integrated version of the WindView software logic analyzer for the target simulator.
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  23. Question 14. What Is Mutex ?

    Answer :

    Mutex is mutual exclusion, which provides exclusive hold on resource .

    In vxworks mutual exclusion semaphore supports different features:

    • ownership
    • recursion
    • Deletion safety
    • priority inversion and priority inheritance.
  24. Question 15. Difference B/w Taskdelay And Nanosleep?

    Answer :

    Taskdelay Wind vxworks: puts a task in delayed state for specified ticks,

    Nanosleep posix : puts process in sleep for specified nano seconds.

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