VxWorks Interview FAQ's by sreekanthreddy


tutorials used for developing and attend interview questions

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									HP (: Hewlett Packard :)

    1. Why Vx works is used for the project?

    Cos code had to be dumped into another machine, which require bounded time response and cross

    2. What r different tools in tornado?

    Editor, compiler, linker, loader, debugger, simulator

    3. Why the variables in registers are not accessible?

    To access variables in registers we need communicating media. So using Modbus protocol we develop
    that environment

    4. How will u debug the program in tornado ?

    Using debugging tool.

    5. How simulator works in tornado?

Simulator works as a target machine in tornado. So that we can dump our code into simulator to check the

    6. What is difference between signals and interrupts?

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.

    7. What does task table (context) contain?

    Task context contain Cpu registers, floating point register, stack etc.

    8. What is priority inversion?

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

    9. How can u over come that?

    Using priority inversion safe.

    10. How does priority inversion safe works?

    It will rise the priority of the lowest task to priority of the highest task.

    11. How many tasks are needed for task inversion?

    Min 3 tasks are required

    12. Will every task which has argument as priority inversion safe will raise its priority?


    13. What is reentrancy in Vx works?
        Using reentrancy procedure multiple users can share a single copy of a program during the same
        period. It is memory saving technique.

        14. What is task switching?

        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

        15. What is interrupt latency?

        Time taken to switch from current running task context to Interrupt service routine.

        16. What r scheduling algorithms? ‘

        There are 2 scheduling algorithms in Vx works 1. Priority based preemptive scheduling algorithm(Vx
        works- default) 2. round robin scheduling algorithm. (UNIX default)

        17. What is default scheduling algorithm in Vx works?

        Priority based preemptive scheduling algorithm.

        18. How does watch dog timer works?

        When time over it will do what ever job we assigned to do.

        19. What r different IPCs?

        Shared memory, message queues, semaphores, pipes

        20. Which is the fastest IPC mechanism?


        21. How does synchronization occur in tasks?

        Using semaphores

        22. What r different types of semaphores? Explain how they work?

        Binary semaphore, mutual exclusion semaphore (Mutex), counting semaphore.

        23. Tell me syntax of mutual exclusion semaphore?



 What is modus protocol? How it works?

Modbus protocol is application layer protocol used for serial communication

    What is difference between Vx works and GPOS?

Vx works doesn’t have any kernel layer. It has four process states. Whereas GPOS have 9 process states.
Vx works is good in handling interrupts. GPOS doesn’t handle interrupts in kernel layer.

Process is light in RTOS, process is heavy in GPOS.

Scheduling algorithms and task priorities can be changes which is not possible in GPOS.

   Have u worked on interrupt service routines?


   How will u handle them in Vx works?

We set some time for interrupt when time over it will jump to the memory where the interrupt service routine has
   been written

   what is difference between RTOS and GPOS? How will u decide that coding must need RTOS?

       If we want code must respond in deputed time and if we want to change task priorities and scheduling
    techniques then we go for RTOS.

   In which domain u worked in Vx works? Application side or OS layer side?

OS layer side

   What is storage space in Vx works?

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