2016年嵌入式面試題及答案
嵌入式面試有什么最新問題呢?下面跟yjbys小編一起來了解吧!
1.static變量和static 函數各有什么特點?
static變量分兩種，局部變量和全局變量，他們都放在全局數據區(我覺得表達不準確。全局靜態變量本文件可見，局部靜態變量在在定義的block內可見;static函數也放在全局數據區，外部文件不可見;
3.描述一下嵌入式基于ROM的運行方式基于ram的運行方式有什么區別。rom運行方式是指指令從rom中取出，首先對rom有一定要求(例如按 block進行讀寫nand flash就不支持rom運行，同時由于rom讀寫的`限制，無法完成異常處理，即異常處理函數肯定放在ram中)。在有區別就是片選不一樣。
4.task 有幾種狀態?就緒、掛起、阻塞、睡眠、運行
5.task 有幾種通訊方式?共享內存、信號量、消息隊列和管道、socket
6.C函數允許重入嗎?函數的重入和不可重入是和函數本身有關的,例如一個字符串拷貝的函數就是可重入的,而一個在函數中調用了I/O,分配內存是就可能是不重入的,是否重入要看調用的庫函數是否重入的.現在Windows平臺下的C庫已經支持多線程了,所以如果你調用的是多線程版的C運行庫,應該都是可重入的.
7.嵌入式操作系統和通用操作系統有什么差別?多優先級，搶占型，實時操作系統。嵌入式操作系統一般沒有UI，體積小，實時性強，對穩定性要求更高。嵌入式操作系統強調實時性，并且可裁減。要求系統資源的消耗要盡可能的小。
國外嵌入式面試題：
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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