Interrupt DMA and Watchdog Timer Embedded Interview Questions Basics Tutorials

How does the interrupt architecture works?

Interrupt architecture allows the use of interrupt by the processor whenever an Input/output is ready for the processing. The processor in this case calls a special function to handle the request that comes and leave all the work that is getting performed at that time. The special function that is known as interrupt handler or the interrupt service routine consists of all the input, and output queries, or the interrupts handled by it. It is an efficient and simple way to handle the interrupts. It uses only one function to deal with the interrupts. There are properties of starvation that can creep in when handling the input/output requests. The data can be lost if the interrupt doesn’t get handled before the time runs out. This is a technique that is use to deal with the short processes that involve input and output.

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How does the interrupts handle by using the threads?

The interrupts that comes in between the input/output operations gets detected when the input/output devices are ready. The interrupt never gets handled directly rather, it sends the interrupt signal to the thread to the input/output device that is ready to allow the thread to take necessary actions. The thread uses the signaling concept that allows the initialization to be done using the semaphore that keeps the states updated and handle the interrupt in an easy way. The input/output device getting the request and it also passes the semaphore to handle. The input/output device takes the semaphore that is ready. The thread is having the minimum latency that uses the first level interrupt handler to handle the interrupts completely. Itallows the priority of the thread to be set and it doesn’t allow the context to be change as well.

What is the function of DMA controlled in embedded system?

DMA stands for Direct Memory Access controller that handles the allocation of the memory dynamically to the components and allows the data to be transferred between the devices. It is used for the communication between different input/output devices. It automatically detects the devices that are present for the transfer of data between the input/output devices.

The interrupt can be used to complete the data transfer between the devices. It is used to give thehigh quality performance as, the input/output device can perform the operations that are in parallel with the code that are in execution phase. It can’t be used in all the systems. It consists of 8-bit micro-controllers that are used to control the overall system in execution.

What are the different types of customization's that is used with the “volatile” keyword?

Volatile keyword is used to show that the value can be changed anytime in the program. It is used for the compiler purpose and for the customization that works with the normal variables that are stored in the memory. There are three types of optimizations associated with the “volatile” keyword:- "Read" optimizations -- allow the variable to be read once and put it in the register. If it is done then there is no re-reading of the variable during each and every time the program is compiled. The value can be used from the cache that is present in the register.- "Write" optimizations -- allow the variable to be written such that the last write of the variable will be considered and it will be processed on. This takes the normal values that are stored in the memory.

- Instruction reordering -- allow to reorder the instructions that are used by the compiler and if any modification are required after being written once. The registers are used to perform the task and keep everything together.

Write a program to show the functionality of Power-save super loop.
To check the loop time of the program the power-save super loop is used. If the average loop time of the program is 1ms, and it requires only few instructions to be checked every second the program will save the state and build a delay that will be caused to read the input on every loop and it saves lot of energy or the power that needs to be used. The function that is required to be performed to show the functionality is:

What are the rules followed by Mutexes?

• Mutex is also called as Mutual Exclusion is a mechanism that is used to show the preemptive environment and allow providing security methods like preventing an unauthorized access to the resources that are getting used in the system. There are several rules that has to be followed to ensure the security policies:
• Mutex are directly managed by the system kernel that provides a secure environment to allow only the applications that passes the security rules and regulations. The mutex consists of objects that are allowed to be called by the kernel.
• Mutex can have only one process at a time in its area that is owned by the process using it.This allows less conflict between the different applications or processes that wait for their turn to execute it in the kernel area.
• Mutex can be allocated to another mutex that is running some task at a particular time and allow the kernel to have synchronization in between them.
• If Mutex is allocated to some other process then the area will consist of the process till the area is having the process in it.

Why does preemptive multi-threading used to solve the central controller problem?

Multi-threading provide lot of functionality to the system to allow more than one task can be run at a time. It allows a process to execute faster with less difficulty. But, if there any problem comes in any program or the process than the entire system comes to a halt and slows down the whole system. To control the behavior of this the preemptive multi-threading is used.The control in this case is being shifted from one process to another at any time according to the requirement provided. It allows the program to give the control to another program that is having the higher priority. It includes of many problems like giving of a control by a process half way through in execution and the preemption of the process takes place then the data will be entered as corrupted in the memory location, multi-threading keeps the synchronization that is to be performed between different components of the system and the program and try to avoid the problem mentioned above.

What is the purpose of using critical sections?

Critical section allows the process to run in an area that is defined by that process only. It is a sequence of instructions that can be corrupted if any other process tries to interrupt it.This process allow the operating system to give the synchronization objects that are used to monitor the processes that are up and running so that no other process will get executed till the critical region consists of a process that is already running. The example includes removal of the data from a queue running in a critical section and if not protected then it can be interrupted and the data have chances of getting corrupted. The processes exit from the critical section as soon as they finish the execution so that the chances can be given to other processes that are waiting for their chance to come.

What is the function of Watchdog timer in embedded system?

The embedded system should have a function that can allow the fixing the system if anything goes wrong with it. Watchdog timer is a tool that is used in embedded system and having a long-fuse that runs several seconds. Watchdog timer includes the automated timing control that count down the number from max to 0 and when the counter reaches the zero, this WDT reset the micro-controller that gets turned off when the timer was in initial phases. Watchdog require the user to put some value before it runs out of time and reset the whole process as this can harm the data and the system. Resetting by WDT can be done when the process is half complete. Watchdog timer have the counter that is used to watch the processes that are running and if there is any issue occurs then WDT itself times out. The resetting of the system will be done to always give it the best possible way to execute the process.


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