1) Explain what is embedded system in a computer system? Top 18 Embedded Systems Interview Questions & Answers . Download PDF. Hardware. Processor. Memory. Timers. I/O circuits. System application specific circuits. Software. It ensures the availability of System Memory. It checks the. + Embedded Systems Interview Questions and Answers, Question1: What is the difference between embedded systems and the system in which rtos is.
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+ Embedded C Interview Questions and Answers, Question1: What is the use of In an embedded system, a certain event must be entertained in strictly. Learn Embedded Systems based Questions and Answers for technical interview, types, characteristics, interview questions on Embedded. The following Embedded Systems questions will help you prepare for interviews and online selection tests conducted during campus.
Can we use printf inside ISR? Can we put breakpoint inside ISR? How to decide whether given processor is using little endian format or big endian format?
What is RTOS? What is the difference between hard real-time and soft real-time OS? What type of scheduling is there in RTOS? What is priority inversion? What is priority inheritance? How many types of IPC mechanism you know? What is semaphore? What is spin lock? What is difference between binary semaphore and mutex?
What is virtual memory? What is kernel paging? 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?
But cat cat 1,2 ,3 does not expand but gives preprocessor warning. Can you have constant volatile variable? Yes, you can have a volatile pointer? Operations involving unsigned and signed — unsigned will be converted to signed Which way of writing infinite loops is more efficient than others? Sanjay Ahuja 1 Who to know whether system uses big endian or little endian format and how to convert among them?
What is forward reference w. How is generic list manipulation function written which accepts elements of any kind? What is the difference between embedded systems and the system in which RTOS is running? How can you define a structure with bit field members? 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? Which parameters decide the size of data type for a processor? What is job of preprocessor, compiler, assembler and linker?
What is the difference between static linking and dynamic linking? How to implement a WD timer in software? Answers by Nigel Jones to some of the questions. Preprocessor 1. Using the define statement, how would you declare a manifest constant that returns the number of seconds in a year? Disregard leap years in your answer. And remember, first impressions count! Write the "standard" MIN macro-that is, a macro that takes two arguments and returns the smaller of the two arguments.
This is important because Sanjay Ahuja 2 until the inline operator becomes part of standard C, macros are the only portable way of generating inline code.
This operator exists in C because it allows the compiler to produce more optimal code than an if-then-else sequence. What is the purpose of the preprocessor directive error? Either you know the answer to this, or you don't. If you don't, see Reference 1. This question is useful for differentiating between normal folks and the nerds. Only the nerds actually read the appendices of C textbooks to find out about such things. Of course, if you aren't looking for a nerd, the candidate better hope she doesn't know the answer.
Infinite loops 4. Infinite loops often arise in embedded systems.
How does you code an infinite loop in C? There are several solutions to this question. Thus, if a candidate gives this as a solution, I'll use it as an opportunity to explore their rationale for doing so. If their answer is basically, "I was taught to do it this way and I haven't thought about it since," it tells me something bad about them.
A third solution is to use a goto : Loop: Sanjay Ahuja Data declarations 5. While writing this article, I consulted textbooks to ensure the syntax was correct.
However, I expect to be asked this question or something close to it when I'm being interviewed. Consequently, I make sure I know the answers, at least for the few hours of the interview. Candidates who don't know all the answers or at least most of them are simply unprepared for the interview. If they can't be prepared for the interview, what will they be prepared for? Static 6. What are the uses of the keyword static? This simple question is rarely answered completely. It is not accessible by functions within any other module.
That is, the scope of the function is localized to the module within which it is declared Most candidates get the first part correct. A reasonable number get the second part correct, while a pitiful number understand the third answer.
This is a serious weakness in a candidate, since he obviously doesn't understand the importance and benefits of localizing the scope of both data and code. Const 7. What does the keyword const mean? As soon as the interviewee says "const means constant," I know I'm dealing with an amateur. Dan Saks has exhaustively covered const in the last year, such that every reader of ESP should be extremely familiar with what const can and cannot do for you.
If you haven't been reading that column, suffice it to say that const means "read-only. If you want the detailed answer, read Saks' columns-carefully! If the candidate gets the answer correct, I'll ask him these supplemental questions: What do the following declarations mean?
The third means a is a pointer to a const integer that is, the integer isn't modifiable, but the pointer is. The fourth declares a to be a const pointer to an integer that is, the integer pointed to by a is modifiable, but the pointer is not.
The final declaration declares a to be a const pointer to a const integer that is, neither the integer pointed to by a, nor the pointer itself may be modified. If the candidate correctly answers these questions, I'll be impressed. Incidentally, you might wonder why I put so much emphasis on const, since it is easy to write a correctly functioning program without ever using it. In effect, declaring a parameter const tells the user about its intended usage. If you spend a lot of time cleaning up the mess left by other people, you'll quickly learn to appreciate this extra piece of information.
Of course, programmers who use const , rarely leave a mess for others to clean up. In short, Sanjay Ahuja 5 they tend to have fewer bugs Volatile 8. What does the keyword volatile mean? A variable declared static within the body of a function maintains its value between function invocations.
A variable declared static within a module, but outside the body of a function is accessible by all functions within that module. It is not accessible by functions within any other module. That is, it is a localized global. Functions declared static within a module may only be called by other functions within that module.
That is, the scope of the function is localized to the module within which it is declared. Accessing Fixed Memory Locations?
Embedded systems are often characterized by requiring the programmer to access a specific memory location.
On a certain project it is required to set an integer variable at the absolute address 0x67a9 to the value 0xaa The compiler is a pure ANSI compiler. Write code to accomplish this task. This problem tests whether you know that it is legal to typecast an integer to a pointer in order to access an absolute location.
The exact syntax varies depending upon one's style. However, I would typically be looking for something like this:. Inline functions property says whenever it will called, it will copy the complete definition of that function. Recursive function declared as inline creates the burden on the compilers execution. Explain Scope Of Static Variables? Static variables can only be accessed in the files were they are declared. Static variable within the scope of a function store it's values in consecutive calls of that function.
Static functions can only be called within the file they are defined. What Is Interrupt Latency? Interrupt latency refers to the amount of time between when an interrupt is triggered and when the interrupt is seen by software. If the language supports only 3 features i;e data encapsulation, data abstraction and polymorphism. If the language supports all the 4 features i;e encapsulation, abstraction, polymorphism and also inheritance then it is said to be object oriented programming language.
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.
Macros and inline functions increased the size of executable code. Because in C when you say the name of the array it means the address of the first element. Hence it is impossible to pass by value in C. Explain What Is Interrupt Latency? How Can We Reduce It? Interrupt latency is the time required to return from the interrupt service routine after tackling a particular interrupt.
We can reduce it by writing smaller ISR routines. A variable should be declared volatile whenever its value could change unexpectedly. In practice, only three types of variables could change: The addition of a 'const' qualifier indicates that the relevant part of the program may not modify the variable. It will return a 4 byte address value.
Because is a signed integer varies from compiler to compiler. Yes structures can be passed to functions by value. Though passing by value has two disadvantages: Const and volatile keywords should not be used together because both are opposite in nature.
A variable is declared as "const" means it's value is not able to be changed but if it is declared as "Volatile" then it is not under control. Four types of storage classes are there in c. Auto 2. Register 3.
Static 4. Extern or Global. Pointers In C? You can define structure bit field members with Dot operators. Fifo First In Last Out is a memory structure where data can be stored and retrieved in the order of its entry only. This is a queue,wheras Memory is a storage device which can hold data dynamically or at any desired locations and can be retrieved in any order.
This means that every program must have a main somewhere. Why Is It Required? Anti aliasing filter reduces errors due to aliasing. Otherwise, aliasing errors will result. Typically a 3.
A fourth order Butterworth filter can be made as cascade of two second order LP filters with zeta of 0. One can use a bilinear transformation approach for realizing second order LP filters. Using this technique described well in many texts, one can make two second order LP filters and cascade them. Is An Embedded System? In the x86 processor architecture, memory addresses are specified in two parts called the segment and the offset.
One usually thinks of the segment as specifying the beginning of a block of memory allocated by the system and the offset as an index into it. Segment values are stored in the segment registers. There are four or more segment registers: Most memory operations accept a segment override prefix that allows use of a segment register other than the default one. What Is Plc System? We cannot sleep in interrupt context so semaphores and mutex can't be used.
Spinlocks can be used for locking in interrupt context. Verification is a front end process and testing is a post silicon process. Verification is to verify the functionality of the design during the design cycle.
Testing is finding manufacturing faults. Explain Can Microcontroller Work Independently? Obviously, it can work independently. But to see the output we need certain output devices like LED, Buzzer can be connected to check its functionality. What Is 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. Mutual exclusion often abbreviated to 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.
But unnecessary memory wastage. And pointers are always passed by reference. Macro is expanded by preprocessor and inline function are expanded by compiler. More over inline functions are used to overcome the overhead of function calls. Macros are used to maintain the readability and easy maintenance of the code. 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 static variable is within the file if it is static global. Scope of static variable is within the function if variable is declared local to a function. But the life time is throughout the program. 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. Virtual memory is a computer system technique which gives an application program the impression that it has contiguous working memory an address space , while in fact it may be physically fragmented and may even overflow on to disk storage.
Systems that use this technique make programming of large applications easier and use real physical memory e. RAM more efficiently than those without virtual memory. What Is Concurrency?
Concurrency is nothing but execution of different transactions simultaneously on one single resource. Dead lock: A group of threads are waiting for resources held by others in the group. None of them will ever make progress. An example of a deadlock which may occur in database products is the following. Client applications using the database may require exclusive access to a table, and in order to gain exclusive access they ask for a lock.
If one client application holds a lock on a table and attempts to obtain the lock on a second table that is already held by a second client application, this may lead to deadlock if the second application then attempts to obtain the lock that is held by the first application.
A thread may wait indefinitely because other threads keep coming in and getting the requested resources before this thread does. Note that resource is being actively used and the thread will stop waiting if other threads stop coming in. High priority thread:. Linux Embedded Systems Tutorial. Embedded Systems Practice Tests. IT Skills. Management Skills. Communication Skills. Business Skills. Digital Marketing Skills.
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All Practice Tests. They can be implemented as: Even if data is input and output as 8- or bit quantities, it is worth considering processing them as 32bit quantities Question However, I would typically be looking for something like this: B derived from A.
C derived from A and B. B derived from A and C derived from A. Extern or Global Question Programming logical control system. DMA deals with Physical addresses. But, DMA controller is a device which directly drives the data and address bus during data transfer. So, it is purely Physical address. That is why when writing the device drivers, the physical address of the data buffer has to be assigned to the DMA.
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