VxWorks Questions And Answers

1⟩ Explain task spawn in vxworks?

The VxWorks multitasking kernel, wind, uses interrupt-driven, priority-based task scheduling. It features fast context switch times and low interrupt latency. Under VxWorks, any subroutine can be spawned as a separate task, with its own context and stack. Other basic task control facilities allow tasks to be suspended, resumed, deleted, delayed, and moved in priority.

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2⟩ Write a code to connect Hardware interrupt to ISR and explain?

In Keil

void serial_ISR() interrupt 4 using 0

{

}

& in AVR studio

SIGNAL(Inteerupt_no)

{

}

hardware intterupt normally redirects the uC to predefined

addresses. In case of high end processors the interrupt

table will decide the interrupt vector address and whenever

intterrupt pin goes low, the table is searched for type and

source of interrupt.

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3⟩ Suppose there is a global variable & a static global variable.Both gets memory allocated from the data segment. Then how does the visiblity of static global varible gets limited to the file alone (in which it gets declared)

Static variables are local in scope to their module in which

they are defined, but life is throughout the program. Say

for a static variable inside a function cannot be called

from outside the function (because it's not in scope) but is

alive and exists in memory. The next time this function is

entered (within the same program) the same chunk of memory

would be accessed now retaining the variables old value and

no new memory is allocated this time for this variable like

other variables in the function (automatic variables). So

basically the variable persists throughout the program.

Similarly if a static variable is defined in a global space

(say at beginning of file) then this variable will be

accessible only in this file (file scope).

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4⟩ What do you mean by Semaphore and when we will go for using this?

semaphore is used to avoid the effect of dead lock.

there are three types of semaphore .

1)binary semaphore->it is only to acquire and release the

semaphore.zero is used for unavailabel and

one is used for available.

2)counting semaphore->when semaphore is acquired counter is

incremented and when semaphore is released conter is

decremented.when counter is zero it is goes to blocked state.

3)mutual exclusion->it is same as binary semaphore.but it is

used for safty purpose.it is two state locked state and

unlocked state.when semaphore is acquired it is goes to

locked state and when semaphore is released it goes to

unlocked state.

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5⟩ Which RTOS supports Non-Preemptive scheduling? Why other scheduling methods are supported by such Oses?

The standard UNIX kernel is a nonpreemptive kernel; it does

not allow a user process to preempt a process executing in

kernel mode. Once a running process issues a system call and

enters kernel mode, preemptive context switches are disabled

until the system call is completed. Although there are

context switches, a system call may take an arbitrarily long

time to execute without voluntarily giving up the processor.

During that time, the process that made the system call may

delay the execution of a higher-priority, runnable, realtime

process.

The maximum process preemption latency for a nonpreemptive

kernel is the maximum amount of time it can take for the

running, kernel-mode process to switch out of kernel mode

back into user mode and then be preempted by a

higher-priority process. Under these conditions it is not

unusual for worst-case preemption to take seconds, which is

clearly unacceptable for many realtime applications.

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6⟩ What is another for creating a task without using taskspawn?

Instead of taskspawn

taskInit and taskActivate can be used to create task.

taskInit->It will initialize the task at specified address

taskActivate->It will activate the initialised task

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7⟩ What are the various methods to overcome it?

Priority Inheritance is the solution for priority

inversion. whenever a high priority task request for some

resource which is locked by a low priority task, the

priority of lower task is inherited to the priority of the

higher task. The instance it unlocks the resource the

prioity is changed to its original value.

Another solution for this is priority ceiling where you

inherit the priority of the lower task whenever a higher

task is created.Even if the higher priority task doesnot

request for the resource

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8⟩ What is priority inversion?

Priority inversion is a situation where in lower priority

tasks will run blocking higher priority tasks waiting for

resource (mutex). For ex: consider 3 tasks. A, B and C, A

being highest priority task and C is lowest. Look at

sequence of context swaps

A goes for I/O . unlocks mutex.

C was ready to run. So C starts running. locks mutex

B is ready to run. Swaps out C and takes mutex.

A is ready to run. but A is blocked as mutex is locked by B.

but B will never relinqishes the mutex as its higher

priority than C.

The solution to priority inversion is Priority inheritance.

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VxWorks

Home Operating System VxWorks

8 VxWorks Questions And Answers

1⟩ Explain task spawn in vxworks?

2⟩ Write a code to connect Hardware interrupt to ISR and explain?

3⟩ Suppose there is a global variable & a static global variable.Both gets memory allocated from the data segment. Then how does the visiblity of static global varible gets limited to the file alone (in which it gets declared)

4⟩ What do you mean by Semaphore and when we will go for using this?

5⟩ Which RTOS supports Non-Preemptive scheduling? Why other scheduling methods are supported by such Oses?

6⟩ What is another for creating a task without using taskspawn?

7⟩ What are the various methods to overcome it?

8⟩ What is priority inversion?

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VxWorks

Home Operating System VxWorks

8 VxWorks Questions And Answers

1⟩ Explain task spawn in vxworks?

2⟩ Write a code to connect Hardware interrupt to ISR and explain?

3⟩ Suppose there is a global variable & a static global variable.Both gets memory allocated from the data segment. Then how does the visiblity of static global varible gets limited to the file alone (in which it gets declared)

4⟩ What do you mean by Semaphore and when we will go for using this?

5⟩ Which RTOS supports Non-Preemptive scheduling? Why other scheduling methods are supported by such Oses?

6⟩ What is another for creating a task without using taskspawn?

7⟩ What are the various methods to overcome it?

8⟩ What is priority inversion?

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