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嵌入式面试题3(转帖)  

2009-12-10 20:01:06|  分类: 设计参考资料 |  标签: |举报 |字号 订阅

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1.static变量和static 函数各有什么特点?

    static变量分两种,局部变量和全局变量,他们都放在全局数据区(我觉得表达不准确。全局静态变量本文件可见,局部静态变量在在定义的block内可见;static函数也放在全局数据区,外部文件不可见;

    3.描述一下嵌入式基于ROM的运行方式基于ram的运行方式有什么区别。rom运行方式是指指令从rom中取出,首先对rom有一定要求(例如按 block进行读写nand flash就不支持rom运行,同时由于rom读写的限制,无法完成异常处理,即异常处理函数肯定放在ram中)。在有区别就是片选不一样。

    4.task 有几种状态?就绪、挂起、阻塞、睡眠、运行

    5.task 有几种通讯方式?共享内存、信号量、消息队列和管道、socket

    6.C函数允许重入吗?函数的重入和不可重入是和函数本身有关的,例如一个字符串拷贝的函数就是可重入的,而一个在函数中调用了I/O,分配内存是就可能是不重入的,是否重入要看调用的库函数是否重入的.现在Windows平台下的C库已经支持多线程了,所以如果你调用的是多线程版的C运行库,应该都是可重入的.

    7.嵌入式操作系统和通用操作系统有什么差别?多优先级,抢占型,实时操作系统。嵌入式操作系统一般没有UI,体积小,实时性强,对稳定性要求更高。嵌入式操作系统强调实时性,并且可裁减。要求系统资源的消耗要尽可能的小。

国外嵌入式面试题:

Embedded System Interview Questions:

Can structures be passed to the functions by value?

Why cannot arrays be passed by values to functions?

Advantages and disadvantages of using macro and inline functions?

What happens when recursion functions are declared inline?

Scope of static variables?

Difference between object oriented and object based languages?

Multiple inheritance - objects contain howmany multiply inherited ancestor?

What are the 4 different types of inheritance relationship?

How would you find out the no of instance of a class?

Is java a pure object oriented language? Why?

Order of constructor and destructor call in case of multiple inheritance?

Can u have inline virtual functions in a class?

When you inherit a class using private keyword which members of base class are visible to the derived class?

What is the output of printf("\nab\bcd\ref"); -> ef

#define cat(x,y) x##y concatenates x to y. But cat(cat(1,2),3) does not expand but gives preprocessor warning. Why?

Can you have constant volatile variable? Yes, you can have a volatile pointer?

++*ip increments what? it increments what ip points to

Operations involving unsigned and signed — unsigned will be converted to signed

a+++b -> (a++)+b

malloc(sizeof(0)) will return — valid pointer

main() {fork();fork();fork();printf("hello world"); } — will print 8 times.

Array of pts to functions — void (*fptr[10])()

Which way of writing infinite loops is more efficient than others? there are 3ways.

# error — what it does?

How is function itoa() written?

Who to know wether systemuses big endian or little endian format and how to convert among them?

What is interrupt latency?

What is forward reference w.r.t. pointers in c?

How is generic list manipulation function written which accepts elements of any kind?

What is the difference between hard real-time and soft real-time OS?

What is interrupt latency? How can you recuce it?

What is the differnce between embedded systems and the system in which rtos is running?

How can you define a structure with bit field members?

What are the features different in pSOS and vxWorks?

How do you write a function which takes 2 arguments - a byte and a field in the byte and returns the value of the field in that byte?

What are the different storage classes in C?

What are the different qualifiers in C?

What are the different BSD and SVR4 communication mechanisms

Persional Prospectives:

Q1. No they are always passed by reference. Think. Size of structure can be arbitrarily large.

Q2. Same as above.

Q5. Lifetime of process.

Q9. Declare a static variable, class variable, and increment(decrement) for every constructor (destructor) called.

Q11. Constructor. Base to current. Destructor. current to base. Both are done recursuively.

Q13. NONE

Q14. $> acd

ef

->ef is wrong, what happened to acd?

Q16. You can have a constant pointer to a volatile variable but not a constant volatile variable.

Q26. Write a union of int and 2 chars. Store as int retrieve as chars.

Q 27. Time taken between INT req and INT service.

Q33. Study Let us C, Yeshwant Kanetkar

Tech Interviews comment by Taran

Q. 13

Answer posted is wrong.

Public & protected members of base class will be visible to derived class, but not its objects.

Tech Interviews comment by Sumeet

Q1 - YES, a complete structure can be passed. Regarding the size, it is true that they can be very large and hence it is not a good practice to do so. In any case, one can do if one wants to.

Tech Interviews comment by Bhaskar

Q3. When using macro you can’t use data type while passing it. But in Inline function you can have data types so that it can be checked.

e.g MACRO : ADD(a,b)

INLINE : inline void Add(int a,int b );

Tech Interviews comment by VijayaKumar

Q1. Yes structure can be passed by value but the overhead of copying large values will be there. hence not usable. We should pass it by pointer.

Q2. Individual element can be passed by value of course. But not whole array.

Q5. It is alive lifetime of process, and its scope is limited to function in which it is defined.

file1.c

**********

static int i;

void main()

{

……..

}

file2.c

**********

extern int i; //error

If declared global then it is visible in that file only.

Q6. Object oriented language have Inheritance, polymorphism etc. But object based language only deal with object.

Q7. If

class D:public A,B,C

{}

then three ancestors

Q8. public ,private, protected, virtual

Q30. Hard RTS is having deadline defined and it is life critical ,should be reliable. late answer is wrong answer. in Soft RTS,process time should be predictable and reliable.

Tech Interviews comment by Pawan Kumar

Q36.What are the different storage classes in C?

A:Auto,Register,Static,Extern

Tech Interviews comment by MKS

Q5 Scope of static variables is only within the block where it is declared.

But the lifetime is till the process is running

Tech Interviews comment by Satish Parande

Questin???

How can we dynamically allocate memory without using malloc() or calloc() or realloc()?Explain in Breif.

Can any one help in finding this answer to this question……

Tech Interviews comment by Midhun V

In Java, we place even the Main() function inside a CLASS.

But it is not the case with C++.

So, i think this is one of the answers you can say, JAVA is Fully Obejct Oriented.

Tech Interviews comment by vsvraju

Q11 : Base-class constructors are called in the order in which inheritance is specified in the derived-class definition. The order in which the Base-class constructors are specified in the derived-class member initializer list does not effect the order of construction.

Tech Interviews comment by vsvraju

Q 12:

Yes we can have.

you are never guaranteed that a routine is inlined. It is only a suggestion to the compiler. If

the routine is either too complicated or a virtual function,then a static copy of the routine will be placed in the compiled module. Thus, a routine that was coded as inline may cause a performance degradation because it may consume much more space when it is not physically inlined.

With a virtual function, a copy of that routine will be created for every module that has at least one instantiation of that class.

Q 13:

NONE.

None of the Public, Protected and Private data members are visible.

Q 16:

YES. We can have a const volatile variable.

a volatile variable is a variable which can be changed by the extrenal events (like an interrput timers will increment the voltile varible. If you dont want you volatile varibale to be changed then declare them as “const volatile”.

Q 17.

I will explain this with an example:

int a = 10;

int *p = &a;

// suppose &a = 4010 (address of a)

Because both ++ and * are unary operators, the are calculated from right to left –> ++ (*p)

++*p will inrement 4010 by 4 (int size) -> ++*p will have the value 4014.

Q 21:

It will print 8 times. Because, each fork will print twice.

if u flush, (using “fflush”), then it will be printed only once. thats is you need to flush the iostreams.

Q 30:

In Hard RTOS the latency should be less the 20ns (nano sec)

in Soft RTOS the latency range 3ns - 20ns is also acceptable.

Tech Interviews comment by vsvraju

I THINK A BALOON CAN HAVE TO MUCH ELECTRICITY

Tech Interviews comment by SANDRA

Java is not a pure object oriented language as “everything” in java is not an object. It still has primitive data types such as int, char, etc. which are NOT objects. Ruby is an example of a pure object oriented language, where “everything” is an object, even int.

Tech Interviews comment by Karan

16. It is possible to have “const volatile” declaration. This indicates that the variable defined like this is not possible to change within that context. It can be changed by an external event. const declaraion just says that it will be readonly within the context, that area can be modified by an interrupt routine or another process.

18. Operations involving unsigned and signed - The signed data will be converted to unsigned - Refer arithemetic conversion rules in K&R

24. #error is used for displaying an error while compilation. for eg.

#ifdef ABC

printf(”ABC”);

#else

#ifdef DEF

printf(DEF);

#else

#error “Declaration not done”

#endif

30. Hard RTOS is system which will be having major problems if the specified time limit is crossed. For eg. missiles

Soft RTOS is systems which will not be having major problems if the specified limit is crossed. For eg. real time audio steaming.

But for both exceeding the time limit is concidered as error.

31. Interrupt latency is the time period between interrupt on the pin to the execution of 1st instuction in the interrupt routine. THis will depend upon the processor. If the execution time for the instruction is less (like in RISC) this time will also be less. If register storage is required the time will be less in the processors in which remapping of registers is present as this can be done in a single instruction.

32. RTOS systems are embedded systems with time criticality.

33.

Tech Interviews comment by deepak

What is interrupt latency?

It is the time interval between an interrupt has occured till the time it has been serviced.

Mathematically:

Int(lat)= rt+pt+dt

where rt=recognition time

pt=process time

dt=dispatch time

Tech Interviews comment by Ramesh K.B.

Q. Write a function to reverse contents in a single linked list without reversing the links?

Can anyone pls help me out?

Tech Interviews comment by Ramesh K.B.

Q.Can we have a constant volatile variable?

Soln: YES.We can have a const volatile variable.

Volatile variable is one which can be changed by user,ie programmer as well as by the external events.If we declare it as const volatile,then user cannot change but can be changed by the hardware.

Tech Interviews comment by Ramesh K.B.

20.

malloc(sizeof(0)) will return — valid pointer

yes. sizeof(0) –> int size and it is 4

25.

itoa(…)

itoa(pointer to storage buffer,int to convert, base(eg.binary,oct,hex,dec))

33.

typedef struct regset{

unsigned char onebit:1;

unsigned char twobit:2;

….

}regset;

Tech Interviews comment by Ramesh.V

i have an query regarding , interupts in Embedded systems

can we use the interrupt function call same as ordinary function,i.e. can we pass arguments and return values from an ISR routine.

Tech Interviews comment by Sushil Rana

what happens when

we put an infinite loop using for

for(;;)

what is the condition expression value by default.

Tech Interviews comment by Sushil Rana

Write a function to reverse contents in a single linked list without reversing the links?

Can anyone pls help me out?

Count number of nodes in the linear linked list. Let say cnt is the number of nodes and index = 0. You can swap content of index th node and cnt-index th node, each time increment index by 1. All the contents will be reversed.

Tech Interviews comment by Hetal

Scope of static variables?

scope of static variables is limited to the local function in which it is defined and to the functions calling the stattic variable.

Tech Interviews comment by Guneet

How virtual tables are created in case of abstract classes? Is it the same as in non-abstract classes? Virtual tables r created on stack or Heap?

Tech Interviews comment by Satish Parande

why only reference is passed as a parameter in Copy constructor? why not address?

Tech Interviews comment by Satish Parande

is it possible to call delete from the class member function ?

Tech Interviews comment by Mrinmay Biswas

q.3.

—- Inline is only a request that may be rejected also based on optimization policies,while macro is immediately replaced before compilation.

—- type checking is not possible in Macros, but in inline its possible

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