Ans: 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 value of 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.
Ans: 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 volatile keyword.
Ans: 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:
Ans: 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.
Ans: 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 execution of the functions and should be cleaned up by the programmer using the free () function.
Ans: The macro are just symbolic representations and cannot contain data type 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 increase in code space if the function is called many times.
Ans: The hard real time Embedded Systems are the one 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.
Ans: The recursive functions refer to the functions which make calls to it 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.
Ans: 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.
Ans: The const qualifier identifies a specific parameter or variable as read-only attribute to the function or to the entire program. This can come in handy when we are dealing with static data inside function and in a program.
Ans: Yes, although this is not very common. An example is when an interrupt service routine modifies a pointer to a buffer.
Ans: Small loops can be unrolled for higher performance, with the disadvantage of increased code size. When a loop is unrolled, a loop counter needs to be updated less often and fewer branches are executed. If the loop iterates only a few times, it can be fully unrolled, so that the loop overhead completely disappears.
Ans: 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.
Ans: The unsigned int is typecast into the signed value.
Ans: 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 (type of pointer) and the starting address of the memory space.
Ans: The memory leak refers to the uncleared memory may builds up across lifetime of the process. When it comes to a huge value system stalls its execution due to unavailability of the memory. The segmentation fault on the other hand refers to condition when our program tries to access a memory space that has already been freed up.
Ans: 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 endiann”);
else printf (“big endiann”);
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Ans: 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.
Ans: The static function when declared within a specific module is scoped only in that module and can only be accessed from it.
Ans: DMA address deals with physical addresses. It is a device which directly drives the data and address bus during data transfer. So, it is purely physical address.
Ans: For embedded system, the buses used for communication includes
While ISA, EISA, PCI are standard buses for parallel communication used in PCs, computer network devices, etc.
Ans: With embedded system, it is possible to replace dozens or even more of hardware logic gates, input buffers, timing circuits, output drivers, etc. with a relatively cheap microprocessor.
A watchdog timer is an electronic device or electronic card that execute specific operation after certain time period if something goes wrong with an electronic system.
Ans: A semaphore is an abstract datatype or variable that is used for controlling access, by multiple processes to a common resource in a concurrent system such as multiprogramming operating system. Semaphores are commonly used for two purposes:
Ans: Recursion function can be used when you are aware of the number of recursive calls is not excessive. 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.
Ans: Embedded systems require infinite loops for repeatedly processing or monitoring the state of the program. For instance, the case of a program state continuously being verified for any exceptional errors that might just happen during run-time such as memory outage or divide by zero, etc.
Ans: Some of the commonly found errors in embedded systems are:
Ans: Real-time embedded systems are computer systems that monitor, respond or control an external environment. This environment is connected to the computer system through actuators, sensors, and other input-output interfaces.
Ans: Timers in embedded system are used in multiple ways: