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Chapter: Embedded and Real Time Systems - Hardware Accelerates & Networks

Important Questions and Answers: Hardware Accelerates & Networks

Embedded and Real Time Systems - Hardware Accelerates & Networks -

HARDWARE ACCELARATES AND NETWORKS

 

1. Name the important terms of RTOS?

 

Task State Scheduler Shared data Reentrancy

 

2. Define process.

 

Process is a computational unit that processes on a CPU under the control of a scheduling kernel of an OS. It has a process structure, called Process control block. A process defines a sequentially executing program and its state.

3. What is meant by PCB?

 

Process Control Block’ is abbreviated as PCB.PCB is a data structure which contains all the information and components regarding with the process.

 

4. Draw the process state transitions?

 


5. Define task and Task state.

 

A task is a set of computations or actions that processes on a CPU under the control of a scheduling kernel. It also has a process control structure called a task control block that saves at the memory. It has a unique ID. It has states in the system as follows: idle, ready, running, blocked and finished

 

6. Define Task Control Block (TCB)

 

A memory block that holds information of program counter, memory map, the signal dispatch table, signal mask, task ID, CPU state and a kernel stack.

 

7. What is a thread?

 

Thread is a concept in Java and UNIX and it is a light weight sub process or process in an application program. It is controlled by the OS kernel. It has a process structure, called thread stack, at the memory. It has a unique ID .It have states in the system as follows: stating, running, blocked and finished.

 

8. Define Inter process communication.

 

An output from one task passed to another task through the scheduler and use of signals, exception, semaphore, queues, mailbox, pipes, sockets, and RPC.

9. What is shared data problem?

 

If a variable is used in two different processes and another task if interrupts before the operation on that data is completed then the value of the variable may differ from the one expected if the earlier operation had been completed .This ids known as shared data problem.

 

10. Define Semaphore.

 

Semaphore provides a mechanism to let a task wait till another finishes. It is a way of synchronizing concurrent processing operations. When a semaphore is taken by a task then that task has access to the necessary resources. When given the resources unlock. Semaphore can be used as an event flag or as a resource key.

 

11. Define Mutex.

 

A phenomenon for solving the shared data problem is known as semaphore. Mutex is a semaphore that gives at an instance two tasks mutually exclusive access to resources.

 

12. Differentiate counting semaphore and binary semaphore.

 

Binary semaphore

 

When the value of binary semaphore is one it is assumed that no task has taken it and that it has been released. When the value is 0 it is assumed that it has been taken.

 

Counting semaphore

 

Counting semaphore is a semaphore which can be taken and given number of times. Counting semaphores are unsigned integers.

 

13. What is Priority inversion?

 

A problem in which a low priority task inadvertently does not release the process for a higher priority task.

 

14. What is Deadlock situation?

 

A set of processes or threads is deadlocked when each process or thread is waiting for a resource to be freed which is controlled by another process.

 

15. Define Message Queue.

 

A task sending the multiple FIFO or priority messages into a queue for use by another task using queue messages as an input.

 

16. Define Mailbox and Pipe.

A message or message pointer from a task that is addressed to another task.

 

17. Define Socket.

 

It provides the logical link using a protocol between the tasks in a client server or peer to peer environment.

 

18. Define Remote Procedure Call.

 

A method used for connecting two remotely placed methods by using a protocol. Both systems work in the peer to peer communication mode and not in the client server mode.

 

19. What are the goals of RTOS?

 

Facilitating easy sharing of resources

Facilitating easy implantation of the application software

Maximizing system performance

 

Providing management functions for the processes, memory, and I/Os and for other functions for which it is designed.

 

Providing management and organization functions for the devices and files and file like devices.

 

Portability

Interoperability

Providing common set of interfaces.

 

 

20. What is RTOS?

 

An RTOS is an OS for response time controlled and event controlled processes. RTOS is an OS for embedded systems, as these have real time programming issues to solve.

 

21. List the functions of a kernel.

 

Process management

Process creation to deletion

Processing resource requests

Scheduling

IPC

Memory management

I/O management

Device management

 

22. What are the two methods by which a running requests resources?

• Message

• System call

 

23. What are the functions of device manager?

 

Device detection and addition

Device deletion

Device allocation and registration

Detaching and deregistration

Device sharing

 

 

24. List the set of OS command functions for a device

 

Create and open

Write

Read

Close and delete

 

 

25. List the set of command functions of POSIX file system

 

Open

Write

Read

Seek

Close

 

 

26. What are the three methods by which an RTOS responds to a hardware source call on interrupt?

 

Direct call to ISR by an interrupt source

 

Direct call to RTOS by an interrupt source and temporary suspension of a scheduled task.

 

Direct call to RTOS by an interrupt source and scheduling of tasks as well as ISRs by the RTOS.

 

27. Name any two important RTOS.

 

MUCOS

VxWorks

 

28. Write short notes on Vxworks?

 

Vxworks is a popular Real-time multi-tasking operating system for embedded microprocessors and systems.

 

Vxworks can run on many target processors.

It is a UNIX like Real time operating system.

More Reliable

More faster

 

29. What is meant by well tested and debugged RTOS?

 

An RTOS which is thoroughly tested and debugged in a number of situations.

 

30. What is sophisticated multitasking embedded system?

 

A system that has multitasking needs with multiple features and in which the tasks have deadlines that must be adhered to.

 

31. What are the features of UC/OS II?

 

Preemptive

Portable

Scalable

Multitasking

 

32. What is MICRO C/OS II?

 

· It stands for micro-controller operating system(UC/OS II).

· It is a real time kernel

· The other names of MICROC/OS II are MUCOS and UCOS.

 

· The codes are in ‘C’ and Assembly language.

 

33. What are the real time system level functions in UC/OS II? State some?

 

1. Initiating the OS before starting the use of the RTOS fuctions.

 

2 Starting the use of RTOS multi-tasking functions and running the states. 3 Starting the use of RTOS system clock.

 

34. Write the interrupt handling functions?

 

int connect ( ) is the function for handling the Interrupt. int Lock ( ) -> Disable Interrupts.

 

int unlock( ) -> Enable functions.

 

35. Write down the seven task priorities in embedded 'C++'?. define Task _Read ports priority

 

define Task _Excess Refund priority define Task _Deliver priority

 

define Task _Refund priority define Task _Collect priority define Task _Display priority

define Task _Time Date Display priority

 

36. Name any two mailbox related functions.

 

OS_Event *OSMboxCreate(void *mboxMsg)

Void *OSMboxAccept(OS_EVENT *mboxMsg)

 

37. Name any two queue related functions for the inter task communications.

 

· OS_Event  OSQCreate(void **QTop,unsigned byte qSize)

· Unsigned byte OSQPostFront(OS_EVENT *QMsgPointer,void *qmsg)

 

 

38. How is Vx Works TCB helpful for tasks?

 

Provide control information for the OS that includes priority, stack size, state and

options.

 

CPU context of the task that includes PC, SP, CPU registers and task variables.

 

39. What are the various features of Vx Works?

 

VxWorks is a scalable OS

 

RTOS hierarchy includes timers, signals, TCP/IP sockets, queuing functions library, Berkeley ports and sockets, pipes, UNIX compatible loader, language interpreter, shell, debugging tools, linking loader for UNIX.

 

40. What is an active task in the context of Vx Works?

 

Active task means that it is in one of the three states, ready, running, or waiting.

 

41. What are the task service functions supported by Vx Works?

 

taskSpawn()

taskResume()

taskSuspand()

taskDelay()

taskSuspand()

taskInit()

exit()

taskDelete()

 

42. Name any four interrupt service functions supported by Vx Works?

 

intLock()

intVectSet()

intVectGet()

intContext()

 

 

43. Name some of the inter process communication function.

 

semBCreate()

semMCreate()

semCCreate()

semTake()

semDelete()

 

44. Name some of the inter process communication function used for messaging.

 

msgQCreate()

msgQDelete()

msgQSend()

msgQReceive()

 

45. What are Vx Works pipes?

 

VxWorks pipes are thec queues that can be opened and closed like a pipe.pipes are like virtual IO devices that store the messages as FIFO.

 

 

46. What are the different types of scheduling supported by Vx Works?

 

Preemptive priority

Time slicing

 

47. What are the task service functions supported by MUCOS?

 

Void OSInit (void)

Void OSStart(void)

voidOSTickInit(void)

void OSIntEnter(void)

void OSIntExit(void)

 

48. What are the semaphores related functions supported by MUCOS?

 

OS_Event OSSemCreate(unsigned short sem val)

 

Void OSSemPend(OS_Event *eventPointer,unsigned short timeout,unsigned byte *SemErrPointer)

 

unsigned short OSSemAccept(OS_Event*eventPointer)

unsigned short OSSemPost(OS_Event*eventPointer)



 

1. Explain the goals of operating system services.

 

Definition

 

An operating system (os) is Software that shares a computer system's resources (processor, memory, disk space, network, bandwidth and so on) between user’s .and tie

application programs they run

 

Goals

The OS goals are perfection and correctness to achieve the following

 

To hide details of hardware by creating abstraction

 

To allocate resources to process

Effective user interface

 

Structure

When using an OS, the processor in the system runs in two modes.

 

User mode:

 

The user process is permitted to run and use only a subset of functions and instructions in the OS.

 

Supervisory mode:

 

The OS runs the privileged functions and instructions in protected mode and OS. A system can be assumed to have a startup as per below table

 

Kernel

The kernel is the central component of most computer operating systems (OS). Its responsibilities include managing the system's resources


Process management

 

Every program running on a computer, be it a-service or an application, is a process. Most operating systems enable concurrent execution of many processes and programs at once via multitasking, even with one CPU.

 

On the most fundamental of computers multitask is done by simply switching process quickly.

 

Depending on the operating system, as more processes run, either each time slice will become smaller or there will be a longer delay before each process is given a chance to run.

 

Process management involves computing and distributing CPU time as well as other resources.

 

Most operating systems allow a process to be assigned a priority which affects its allocation of CPU time.

 

Interactive operating systems also employ some level of feedback in which the task with which the user is working receives higher priority.

 

Memory management

 

An operating system's memory manager coordinates the use of these various types of memory by tracking which can is available, which is to be allocated or deal located and how to move data between them. This activity, usually referred to as virtual memory management,

 

increases the amount of memory available for each process by making the disk storage seem like main memory. There is a speed penalty associated with using disks or other slower’ storage as

 

memory - if running processes require significantly more RAM than is available, the system may start thrashing. This can happen either because one process requires a large amount or because

 

two or more processes compete for a larger amount of memory than is available. This then leads to constant transfer of each process’s data to slower storage. Another important part of memory

management is managing virtual addresses. If multiple processes are in memory at once,

 

2. Explain the three alternative systems in three RTOS for responding a hardware source call with the diagram.

 

There are three alternative systems for the RTOSs to respond to the hardware source calls from the interrupts.

 

Direct call to ISR by an Interrupting Source

 

A hardware source calls an ISR directly, and ISR just sends a message to the RTOS. On an interrupt the process running at the CPU is interrupted and the ISR corresponding to that source starts executing.

 

RTOS is simply sent a message from the ISR into a mailbox or message queue. It is to inform the RTOS about which ISR has taken control of the CPU.

 

The ISR continues execution of the codes needed interrupt service. The routine sends a message for the RTOS.The message is stored at the memory allotted for RTOS messages.

 

When TSR finishes, the RTOS returns to the interrupted process or reschedules the processes. RTOS action depends on the messages at the mailbox.



Direct call to RTOS by an Interrupting Source and temporary Suspension of a Scheduled Task

 

The ISR send a message for initializing the task and returns after restoring the context. The messages are stored at the memory allotted for RTOS messages.

 

The RTOS now initiates the task to ready state to later encode needed for the interrupt service. The ISR must be short and it simply places the messages. It is the task that runs the remaining codes whenever it is scheduled. RTOS schedules only- the .processes) and switches the contexts between the tasks only.

 

ISR executes only during a temporary suspension of a task.


Direct call to RTOS by an Interrupting Source and Scheduling of Tasks as well as IRS by the RTOS

 

The RTOS intercepts and executes the task needed on return from the ISR without any message for the task from the ISR. This is shown below

 

The routine doesn't T4 any messages but memory sends the IPCs for the needed parameters for a task. Parameters are stored at the memory allotted for the RTOS inputs.

 

The RTOS now calls return and restoration of the context and switches the run later the codes needed for the any other task.

 

The ISR need not be short and simply generates and saves as the IPCs the input parameters. It is the task that runs the codes whenever RTOS schedules not only the tasks but also the ISRs and switches the contexts as well as the tasks as well as the ISRs.

 

3. Explain the scheduler in which RTOS insert into the list and the ready task for sequential execution in a co-operative round robin model.

 

Cooperative means that each ready task cooperates to let a running one finish. None of the tasks does a block anywhere during the ready to finish states. Round robin means that each ready state runs in turn only from the circular queue. The service is in the order in which a task is initiated on interrupt.

 

Worst-case latency is same for each task. It is tcycle

The worst-case latency with this scheduling will be


dt- event detection time

 

st- switching time from one task to another

et -task execution time


 

4. Explain the use of Semaphores for a Task or for the Critical Sections of a Task.

 

Use of a Single Semaphore

 

Semaphore provides a mechanism to let a task wait till another finishes. It is a way of synchronizing concurrent process operations. When a semaphore is 'taken' by a task, then that task has to access to the necessary resources; when given, the resources unlock. Semaphore can be used as an event flag or as a resource key. Resource key is one that permits use of resources like CPU, memory or other functions or critical section codes

 

Semaphore, which is a binary Boolean variable (or it is a signaling variable or notifying variable.)Used as event flag. Semaphore is called binary semaphore when its value is 0 and it is assumed that it has Boolean taken. When its value is l, it is assumed that no task has taken it and that it has been released.


Use of Multiples Semaphores

 

Consider two semaphores. A task I when executing a critical section notifies the os to take the semaphore. os returns information that the semaphore has been taken to l and M. Now, the task I executes the codes of the critical. The OS having been notified about a take semaphore x from I, does not take and OS does not release the o task J and M' But the os returns an semaphore at an instance.


Use of Mutex

 

Mutex is a semaphore that gives at an instance two tasks mutually exclusive access to resources. Use of mutex facilitates mutually exclusive access by two or more process to the resource (CPU). The same’ variable, sem_m, is shared between the various processes. Let

process and process 2 share sem_m and its initial value = l.

Process’s 1 proceeds after sem_m decreases and equals 0 and gets the exclusive access to the CPU.

Process I ends after sem_m increases and equals l; process 2 can now gets exclusive access to the CPU.

 

5. Explain the Rate Monotonic Co-operative scheduling.

 

Cooperative means that each ready task cooperates to let a running one finish. None of the tasks does a block anywhere during the ready to finish states. Round robin means that each ready state runs in turn only from the circular queue. The service

 

is in the order in which a task is initiated on interrupt.

 

Worst-case latency is same for each task. It is tcycle .

The worst-case latency with this scheduling will be:


dt- event detection time

st- switching time from one task to another

et -task execution time



There is cooperative scheduling and each ready task cooperates to let the running one finish. None of the tasks does a block anywhere from the start to finish. Here, however, in case of cyclic scheduling, the round robin is among the ready tasks that run in turn only from a priority wise ordered list. The ordering is according to the precedence of interrupt source and the task.

 

The RTOS scheduler first executes only the first task at the ordered list, and the tcycle equals the period taken by the first task on the list. It is deleted from the list after the first task is executed and the next task becomes the first. Now, if the task in the ordered list is executed in a cyclic order, it is called Cyclic Priority based cooperative Scheduler.

 

The insertions and deletions for forming the ordered list are made only at the beginning of each cycle.

 

Let Pem, be the priority of that task which has the maximum execution time. Then worst latencies for the highest priority and lowest priority tasks will now vary from

 

 

6. Explain the features of Vx Works.

 

VxWorks is a Unix-like real-time operating system made and sold by Wind River Systems of Alameda, California" USA. Like most RTOSes, VxWorks includes a multitasking kernel with pre-emptive scheduling and fast interrupt response, extensive inter-process communications and synchronization facilities, and a file system Major distinguishing features of VxWorks include efficient POSlX-compliant memory management, microprocessor facilities, a shell for user interface, symbolic and source level debugging capabilities, and performance monitoring. VxWorks is generally used in embedded systems. Unlike "native" systems such as UNIX and Forth, VxWorks development is done on a "host" machine running Unix or Windows, crosscompiling target software to run on various "target" CPU architectures as well as on the "host" by means of VxSim. VxWorks has been ported to a number of platforms and now runs on practically any modern CPU that is used in the embedded market. This includes the x 86 families, MIPS, PowerPC, SH-4 and the closely related family of ARM, StrongARM and xScale CPUs

 

VxWorks System Functions and System Tasks

 

The first task that a scheduler executes is UsrRoot from the entrv point of usrRoot0 in file

 

install/Dir/target /config/alI / usr/Confi g. c.

 

It spawns the VxWorks tools and the following tasks. The root terminates after all the initializations. Any root task can be initialized or terminated. The set of functions, tlog Task, logs the system message without current task context I/O.

 

Interrupt handling functions

 

An internal hardware device auto generates an interrupt vector address, ISR- ECTADDR as per the device. Exceptions are defined in the us6r software.

 

ISR Design

 

ISR have the highest priority and can preempt any running task.

An ISR inhibits the execution of the tasks till return’.

 

An IRS does not execute like a task and does not have regular task context. It has special interrupt context'

 

While each task has its own stack" unless and otherwise not permitted -by a special architecture of a System or a processor

 

An ISR should not wait for taking the semaphore or other IPC.

 

ISR should just write the required data at the memory or post an IPC so that it has short codes and most of its functions, execute at tasks.

 

ISR should not use flodting-point functions as these takes longer time to execute.

 

Signals and interrupt handling functions

 

Function 'void sigHandler(int sigNum)' declares a signal servicing routine for a signal identified by sigNum and a signal servicing routine registers a signal as follows:

 

Signal (sigNum, sigISR). The parameters that pass are the sigNum and signal servicing routine name, sigISR.A pointwer pSigCtx associates with the signal context. The signal xcontewxt savwes PC, SP, registers, etc. like an ISR context.

 

The signal ISR calls the following functions:

Call taskRestart0, to restart the task which generated the sigNum.

Call exit0 to terminate the task, which generated the sigNum.

Call longiumpO. This results in starting the. Execution from a memory location.

 

7. Explain the RTOS programming tool MicroC/OS-II.

 

MicroC/O$II (commonly termed PC/O$II or mC/OSi-il), is a low-cost priories-based pie-emptive real time multitasking operating system kernel for microprocessors, written mainly in the C fodarnming language. It is mainly intended for use in embedded systems.

 

Ports

 

It has ports for most popular processors and boards in the market and is suitable for use in safety critical embedded systems such as aviation, medical systems and nuclear installations.

 

Task states

 

pC/OS-[ is a multitasking operating system. Each task is an infinite loop and can be in any one of the following 5 states:

 

Dormant

 

Ready

Running

Waiting

ISR

 

Source files

There are two types of source files.

 

Master header files includes the #include preprocessor commands for all the files of both

types. It is referred to as include.h file Preprocessor dependent


Source files

Two header files at the master are the following:

 

os_cpu.h is the processor definition header file.

The kernel building configuration file is os-cfg.h.

Further two C file are the ISRs and RTOS timer

specifying osjick.c and processor C codes os_cpu_c.c

 

Processor independent source file

 

Two files, MUCOS header and C files, are cos.ii.h and ucos.ii.c. The files for the RTOS core, timer and task are os_colt.c os_time.c and os_task.c. The other codes are in os_mem.c, os_sem.c, os_q.c and os_mbox.c

 

It is a mandatory to use a well tested and debugged RTOS in a sophisticated multitasking embedded system.

 

MUCOS and VxWorks are two important RTOS. MUCOS handles and schedules the task and ISRs

.

 

8. Explain RTOS system level functions with an example

 

MUCOS has system level functions. These are for RTOS initiation and start, RTC ticks initiation and the ISR enter and exit functions.


Functions in this table pass no arguments and return type is void.

 

There is a global variable,OslntNesting.which increments on entering ISR.Global variable OSlntNesting decrements on'exit"from an ISR. Initiating the operating $)stem before starting the use of the RTOS functions

 

Function void OSInit (void) operating system.

Its use is compulsory before functions.

It returns no parameter.

 

Starting use of RTOS multitasking functions and returning the tasks

 

Function void OSStart(void) is used to start the initiated operating system and

create tasks.

 

Its use is compulsory for the multitasking OS kernel operations.

It returns no parameter.

 

Starting the RTOS System clock

 

Function void OsTicklnit(void) is used to initiate the system clock ticks and interrupts at regular intervals as per OS_TICKS_PER_SEC predefined during configuring the

MUCOS.

 

Its use is compulsory for the multitasking OS kernel operations when the timer functions ane to be used.

 

It returns no parameter.

 

Sending message to RTOS taking control al the start of an ISR

 

Function void OSlntEnter(void) is used at the start of an ISR.

 

It is for sending a message to RTOS kernel for taking control. Its use is compulsory to let the multitasking OS kernel, control the nesting of the ISRs in case of occurrences of multiple interrupts of varying priorities.

 

It returns no parameter.


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