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Monday, June 17, 2019

35 Top Embedded Systems Interview Questions and Answers {Updated}

Embedded Systems Interview Questions and Answers for experienced PDF, Read commonly asked Embedded Systems Job Interview Questions with Answers PDF for Freshers.

Read Embedded Systems Interview Questions and Answers

What is a watchdog timer?
A watchdog timer (or computer operating properly timer) is a computer hardware timing device that triggers a system reset if the main program, due to some fault condition, such as a hang, neglects to regularly service the watchdog. The intention is to bring the system back from the hung state into normal operation.

What is semaphore?
In computer science, a semaphore is a protected variable or abstract data type which constitutes the classic method for restricting access to shared resources such as shared memory in a parallel programming environment. A counting semaphore is a counter for a set of available resources, rather than a locked/unlocked flag of a single resource.

What is mutex?
Mutual exclusion (often abbreviated to a mutex) algorithms are used in concurrent programming to avoid the simultaneous use of a common resource, such as a global variable, by pieces of computer code called critical sections.

Can structures be passed to the functions by value?
Yes, structures can be passed by value. But unnecessary memory wastage.

Why cannot arrays be passed by values to functions?
When an array is passed to a function, the array is internally changed to a ‘pointer’. And pointers are always passed by reference.

Advantages and disadvantages of using macro and inline functions?
Advantage: Macros and Inline functions are efficient than calling a normal function. The times spend in calling the function is saved in case of macros and inline functions as these are included directly into the code.
Disadvantage: Macros and inline functions increased the size of the executable code.
The difference in inline functions and macro
1) Macro is expanded by the preprocessor and inline function are expanded by the compiler.
2) Expressions passed as arguments to inline functions are evaluated only once while _expression passed as an argument to inline functions are evaluated more than once.
Moreover inline functions are used to overcome the overhead of function calls. Macros are used to maintain the readability and easy maintenance of the code.

What happens when recursion functions are declared inline?
It is illegal to declare a recursive function as inline. Even a function is declared as inline compiler judges it to be inline or not. Many compilers can also inline expand some recursive functions; recursive macros are typically illegal.

Scope of static variables?
Scope of the static variable is within the file if it is static global. Scope of the static variable is within the function if the variable is declared local to a function.
But the lifetime is throughout the program

What is the difference between a ‘thread’ and a ‘process’?
In computing, a process is an instance of a computer program that is being sequentially executed by a computer system that has the ability to run several computer programs concurrently.
A single process may contain several executable programs (threads) that work together as a coherent whole. One thread might, for example, handle error signals, another might send a message about the error to the user, while a third thread is executing the actual task of the.

What is an Inode?
In computing, an inode is a data structure on a traditional Unix-style file system such as UFS. An inode stores basic information about a regular file, directory, or other file system object.

What is pass by value and pass by reference? How are structure passed as arguments?
The parameter to a function can be a copy of a value that is represented by variable or can be a reference to a memory space that stores the value of a variable. The former is referred to as pass by value and the latter is referred to as pass by reference. The difference is that when parameters are passed by value the changes made to the variable value within the function is not reflected in the caller function, but when passed as reference changes are reflected outside the called function. The structures are always passed by reference.

What is the difference between using a macro and an inline function?
The macro is just symbolic representations and cannot contain datatype differentiations within the parameters that we give. The inline functions can have the data types too defined as a part of them. The disadvantage in using both is that the inclusion of condition checks may lead to an increase in code space if the function is called many times.

What is the volatile keyword used for?
The volatile keyword is used to represent variables that point to memory in other mapped devices. In such a case the value of the variable can be changed outside of a program. The compiler does not do additional optimizations to the code if there is a volatile keyword.

What are hard and soft Real-time systems?
The hard real-time systems are the once that depend on the output very strictly on time. Any late response or delay cannot be tolerated and will always be considered a failure. The soft real-time systems on the other are not very rigid as the hard real-time systems. The performance of the system degrades with the lateness of response, but it is bearable and can be optimized to a certain level for reuse of the result.

What is a semaphore? what are the different types of semaphore?
The semaphore is an abstract data store that is used to control resource accesses across the various threads of execution or across different processes. There are two types of semaphores:
• The binary semaphore which can take only 0,1 values. (used when there is contention for a single resource entity)
• The counting semaphore which can take incremental values to a certain limit (used when a number of resources is limited).

Write a constant time-consuming statement lot finding out If a given number Is a power of 2?
If n is the given number, then the expression (n & (n-1)) = 0 gives the logical output depicting if it is a power of 2 or not, if (n & (n-1) == 0) printf (“The given number is a power of 2”);

What are recursive functions? Can we make them in line?
The recursive functions refer to the functions which make calls to itself before giving out the final result. These can be declared as in-line functions and the compiler will allocate the memory space intended for the first call of the function.

What is the size of the int, char and float data types?
The size of the char and int are always dependent on the underlying operating system or firmware. This is limited to the number of address lines in the address bus.
The int usually takes up a value of 2 bytes or 4 bytes. The char can take up a space of 1 or 2 bytes. The float data type takes up a value of 4 bytes.

What does malloc do? What will happen if we have a statement like a malloc(sizeof(0));
Malloc is the function that is used for dynamically allocating memory to the different variables. The malloc returns a memory pointer of void type (void *). The statement malloc(sizeof(0)) returns a valid integer pointer because sizeof(0) represents the size of memory taken up by the integer value of 0. The memory allocated by memory is not automatically cleaned up by the compiler after the execution of the functions and should be cleaned up by the programmer using the free() function.

What is meant by a forward reference in C?
The forward reference refers to the case when we point an address space of a smaller data type with a pointer of a bigger data type This can be pictured as allocating memory in single bytes and accessing it with integer pointer as chunks of 4.

What is the order of calling for the constructors and destructors in case of objects of inherited classes?
The constructors are called with base class first order and the destructors are called in the child first order. That is, the if we have 2 levels of inheritance A (base)-> B (inherit 1)-> C (inherit 2) then the constructor A is called first followed by B and C. The C destructor is called first followed by B and A.

Explain the properties of an Object-oriented programming language.
• Encapsulation: The data that are related to the specific object is contained inside the object structure and hidden from the other entities of the environment
• Polymorphism: The mechanism by which the same pointer can refer to different types of objects, which are basically linked by some generic commonality.
• Abstraction: Hiding the data and implementation details from the real objects. The framework of reference is still present to be used by the other objects.
• Inheritance: The way to take out the common features and have them as separate object entities only to be reused by the other objects in a modular fashion.

What do you mean by interrupt latency?
Interrupt latency refers to the time taken for the system to start the handler for the specific interrupt. The time from the time of arrival of interrupt to the time it is being handled.

What typecast is applied when we have a signed and an unsigned int in an expression?
The unsigned int is typecast into the signed value.

How are variables mapped across to the various memories by the C compiler?
The compiler maintains the symbol table which has the related information of all the variable names along with the length of the allocated space, the access unit length for the pointer (the type of pointer) and the starting address of the memory space.

What is a memory leak? What is a segmentation fault?
The memory leak refers to the uncleared memory mat builds up across my lifetime of the process. When it comes to a huge value me system stalls its execution due to my unavailability of the memory. The segmentation fault, on the other hand, refers to my condition when our program tries to access a memory space that has already been freed up.

What is ISR? Can they be passed any parameter and can they return a value?
ISR refers to the Interrupt Service Routines. These are procedures stored at specific memory addresses which are called when a certain type of interrupt occurs. The ISRs cannot return a value and they cannot be passed any parameters.

a=7; b=8; x=a++-b; printf(“%d”, x ); What does this code give as output?
The compiler understands the statement expression a–b by taking off as many operators as it makes sense to a variable. So (a++) is taken as a parameter and then the expression becomes 8-8 which in turn gives the x value as 0. Thus the output value is 0.

What are little endian and big endian types of storage? How can you identify which type of allocation a system follows?
The little-endian memory representation allocates the least address to the least significant bit and the big-endian is where the highest significant bit takes up the least addressed memory space. We can Identify the system’s usage by defining an integer value and accessing it as a character.
int p=0x2;
if(* (char *) &p == 0x2) printf (“little endian\n”); else printf (“big endian\n”);

What is the scope of a function that is declared as static?
The static function when declared within a specific module is scoped only in that module and can only be accessed from it.

What is the use of having the const qualifier?
The const qualifier identifies a specific parameter or variable as a read-only attribute to the function or to the entire program. This can come in handy when we are dealing with static data inside a function and in a program.

Why do we need an infinite loop in embedded systems development? What are the different ways by which you can code in an infinite loop?
The infinite loops are coded in to give a delay or sleep to the program execution for a specific amount of clock ticks. They can be implemented as:
goto Loop;

What is the difference between embedded systems and the system in which rtos is running?
Embedded system is just combination of s/w and h/w that is some embedded sys may have os some may not and rtos is an os.

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