Embedded systems combine both computer hardware and software. They are often designed for specific functions or to function within a larger system. Some of the locations for embedded systems include household appliances, consumer electronics, industrial machines, automobiles, cameras, airplanes, toys, and mobile devices. This article will discuss some of the common embedded systems interview questions to expect in your upcoming interview if you have been shortlisted for one.
1. Can You Tell Us What An Embedded System Is
An embedded system combines hardware and software components that perform specific functions within a larger system. It has several components, including input/output peripherals, a microcontroller/ microprocessor, memory, and software responsible for the system’s behavior. Some common embedded systems applications include medical devices, automotive, consumer electronics, and industrial control.
2. What Do You Understand By Interrupt Latency?
Interrupt latency refers to the duration taken by an embedded system to recognize an interrupt request and respond to it. The system must respond to such interrupts to maintain peak performance quickly. Factors that affect interrupt latency include the system clock speed, interrupt priority, and the interrupt handling code.
3. Differentiate Preemptive And Cooperative Scheduling
Embedded systems offer preemptive and cooperative scheduling, which works for different tasks. Some of the differences include the following:
- Preemptive scheduling empowers more pressing tasks to interrupt the lower-priority tasks, while cooperative scheduling ensures that lower-priority tasks allow the higher-priority ones to yield such control.
- Preemptive scheduling is mostly recommended for real-time systems, which require timing, while cooperative scheduling works for non-real-time systems.
- Preemptive scheduling is generally implemented using a priority-based scheduler, which assigns tasks priorities based on their importance which is not the same for cooperative schedulers. The scheduler’s job is to ensure that the high-priority tasks are dealt with first.
4. Embedded Systems Have Timers. Mention The Uses Of Timers In These Systems
Timers have several uses in embedded systems, which include:
- Time slicing for different tasks
- Helping in the scheduling of different tasks in RTOS
- Initiating events once the comparison of preset times is complete
- Finding the time interval between two related or non-related events
- Initiating an event once the present time delay is over
- Acting as a real-time clock for the system
- Multiplexing time division
5. Differentiate Between A Microcontroller And A Microprocessor
A microcontroller can be defined as a complete computer system found on a single chip. The chip generally includes components such as input/output peripherals, memory, and the processor. It is mostly used on embedded systems because of its space and power constraints. Other factors that encourage using microcontrollers include low cost and low power consumption.
On the other hand, a microprocessor is the central processing unit of a computer. It can’t exist alone and therefore requires components such as input/output peripherals and memory. These systems are mostly used in systems that require high performance and flexibility.
6. Define A Real-Time Operating System
A real-time operating system, popularly known as RTOS, normally refers to an operating system that works for real-time applications which prioritize timing and predictability. It comes with different mechanisms needed to allocate system resources, schedule tasks and manage interruptions, ensuring that critical tasks are executed at the right time. RTOS comes with components such as device drivers, kernel, and several application programming interfaces, popularly known as API. These components support software interaction with the system. Some of the features of an RTOS include the following:
- Ability to predictably handle exceptions and interrupts
- Ability to prioritize tasks
- Ability to offer deterministic response times
Like embedded systems, real-time operating systems can be used in aerospace, automotive, industrial control, and medical devices.
7. Define A Watchdog Timer
A watchdog timer in embedded systems is one of the many timers used to identify and recover from system failure. It is generally set to a specific timeout value, giving it the authority to reset the system if it does not reset it before its expiry. The timer, therefore, ensures that the system remains in a known state by helping it recover from errors capable of making it lock or malfunction. This explains why the timer is mostly used in safety-critical applications, which generally cause severe consequences upon system failure. It’s mandatory for the software to reset the timer to prevent the system from resetting periodically.
8. Define A DMA Controller
A DMA controller, popularly known as a direct memory access controller, transfers data between I/O devices and memory without needing a processor. It is mostly preferred for data transfer because it transfers data at much higher speeds than the processor. It can also free up the processor, allowing it to perform other tasks as the data transfers. The DMA controller must first request access to the system bus before data transfer. The bus is then released after the data transfer, and the processor is signaled at the end of the transfer. Some of the use cases of DMA controllers include networking equipment, multimedia systems, and storage devices.
9. Define A Stack
A stack can be defined as a data structure used for temporary data storage. It also returns function calls’ addresses in programs. Calling a function pushes the arguments onto the stack, similar to the return address. The function is then empowered to access the argument and compute it, popping the return address from the stack and returning control to the calling function once it is done. Additionally, the stack stores function call frames, local variables, and essential data, making it an important data structure in embedded systems. It is also worth noting that the system design determines its size.
10. Define A Cache In Embedded Systems
A cache is a common component in embedded systems. It is a small high-speed memory that stores frequently used instructions and data. The processor generally checks the cache before accessing data or instructions to check if they are already stored. The presence of data or instructions in the cache means that the processor can easily access them without going to the main memory. The cache improves system performance by minimizing the number of memory accesses. It can be located on a separate chip, the motherboard, or the processor.
11. Explain What A Bootloader Is
A bootloader is a common software in embedded systems and microcontrollers that loads and starts the main application program. Unlike other software pieces, it is found in a separate memory section from the main application and can be executed by powering or resetting the system. Some of the storage devices from which the bootloader loads the main application program includes flash memory. It also allows new versions of a program to be loaded and installed, meaning that it can also help update the main application program. In embedded systems, bootloaders simplify the software update process, enabling system firmware remote updates.
12. Define A Memory Mapped I/O
Embedded systems use a technique known as memory-mapped I/O to access input/output (I/O) devices like memory locations. This technique uses the same data transfer operations and instructions to access memory. Memory-mapped I/O works by mapping the I/O device into the same address space as the memory, making the processor read or write to a particular memory address associated with the device. It, therefore, offers a simple and efficient technique for accessing related devices, which explains why it is usually used in systems with limited hardware resources.
13. Define An Interrupt
An interrupt is a signal sent to the processor by an external device indicating that an event has occurred. The external device can either be a sensor or an input/output device. Receiving an interrupt makes the processor stop its current task and switch to a special interrupt handler routine to process the interrupt and handle the event. The interrupt is normally included in an embedded system’s programming to allow a quick and efficient response to an external event by the processor. They are generally software or hardware generated and are often used for several applications, such as input/output handling and time-critical operations.
14. What Do You Understand By A Memory Pool?
A memory pool is a block allocated for specific tasks or data structures. It is included in embedded systems to improve memory management reliability and efficiency by offering a controlled and reliable memory source for tasks or components. These pools are usually implemented using fixed-size memory blocks, further divided into smaller blocks to be allocated to data structures or tasks as necessary. They are also normally configured to support allocation strategies such as best-fit, worst-fit, and first-fit based on the specific system requirements.
15. Do You Know What A Device Driver Is In Embedded Systems?
The device driver is one of the embedded systems’ most common software components. It interfaces with a range of hardware devices, including storage devices and input/output devices, permitting communication between other software components and the device without having to master the low-level details of the latter’s operation. Developers need this device to use several hardware components in their applications. They can either be offered by the device manufacturer or developed by a system developer.
16. Do You Know What An Embedded Linux System Is?
Yes. Embedded Linux systems use the Linux OS as their primary software component. They are scalable, flexible, and reliable, which explains why they are used in several applications. They have several hardware components, such as memory, input/output devices, and microprocessors, for optimal functioning. They also have a customized version of the Linux OS to meet specific system requirements. Some of the applications of these systems include storage, automotive systems, networking, and multimedia.
17. Define A JTAG Interface In Embedded Systems
A JTAG Interface, popularly known as a Joint Test Action Group interface, is a hardware interface that accesses and debugs an embedded system’s internal components. It offers a standard interface that helps access and control a microprocessor’s test, and on-chip debug’s features. This type of interface allows developers to conduct several diagnostic and debugging tasks. One of the reasons why they are available in embedded systems is to allow easy access and control of a system’s internal components required for performing diagnostic and debugging tasks that other tools or interfaces cannot.
18. What Do You Understand By A Bit-Banging Interface?
A bit-banging interface is a communication method that manually manipulates a data bus or communication line, allowing easier communication with hardware devices. Such interfaces allow developers to easily access and communicate with hardware devices through simple, efficient software algorithms. They are generally used for several applications, such as communication protocols, input/output handling, and sensor interfacing.
19. Do You Know What A Real-Time Clock Is?
A real-time clock, popularly referred to as RTC, is a hardware component that tracks an embedded system’s current date and time. It is normally powered by a supercapacitor or backup battery, which saves it from power surges or downtimes. It can maintain the embedded system’s date and time even with the power source off. The real-time clock, therefore, offers an accurate and reliable time source for different applications that demand precise scheduling and timing. Some of its common uses include monitoring systems and industrial automation.
20. Define A State Machine
A state machine is yet another common software component in embedded systems. It uses finite states and transitions to model the behavior of a process or system. It is a complete unit that consists of a combination of states, a set of transitions between them, and a combination of actions or behaviors associated with every state or transition. State machines are normally included in embedded systems programming to offer developers a mechanism for controlling and modeling complex systems or processes behaviors. This explains why they are used in applications such as user interfaces, control systems, and communication protocols.
21. Differentiate A Cache From A Stack
A cache is a minuscule high-speed memory that stores frequently used instructions and data. It is the first stop for the processor when it needs to access data or instructions. If it finds data or instructions in the cache, the processor accesses them quicker than it could have if they were in the main memory. Caches reduce the number of required memory accesses, improving system performance, and can be either software or hardware-based.
On the other hand, a stack is a data structure that temporarily stores data and returns available call addresses in a program. Upon calling a function, the function pushes arguments and the return address on the stack for easier access. Stacks, therefore, store function call frames, local variables, and a range of important data.
22. Define An MMIO Interface In Embedded Systems
The MMIO Interface is also known as the memory-mapped input/output interface. It permits easy access to input/output devices via the system’s memory address space. The interface maps devices into the memory address space, enabling easier access by memory read and write applications. The main reason why MMIO interfaces are included in embedded systems programming is that they offer developers an efficient and simple means of accessing I/O devices, as they don’t need any specialized interfaces or complex device drivers. This explains why they are used in multimedia systems, storage, and networking.
23. Mention The Different Types Of Embedded Systems Based On The Function
Embedded systems are usually categorized based on function and performance. Those categorized based on function include:
- Mobile embedded systems- Such systems include digital cameras, normally designed for portability.
- Networked embedded systems- Networked embedded systems connect to networks and offer output data to other systems. A great example is home security systems.
- Standalone embedded system- A standalone embedded system includes MP3 players and calculators. They don’t need a host to perform specialized tasks.
- Real-time embedded systems- Real-time embedded systems offer output within a defined time interval. They include traffic control systems.
24. Mention Embedded Systems By Performance Requirements
There are three main embedded systems based on performance requirements, namely:
- Small-scale embedded systems- These systems use up to an 8-bit controller and are best suited for small-scale usage.
- Medium-scale embedded systems- These systems either use a 16-bit or 32-bit microcontroller. They can also use one or several units based on the system’s complexity.
- Sophisticated-scale embedded systems- These systems generally use complex hardware and software components.
25. Mention Some Of The Common Applications Of Embedded Systems
Embedded systems are used in several industries for different applications. Some of the common include:
- Healthcare industry- In the healthcare industry, embedded systems are used in various devices and systems, such as surgical and treatment devices, diagnostics and imaging tools, and patient monitoring systems.
- Military and defense industry- Some common devices and systems that use embedded systems in the military and defense industry include C4ISR systems, autonomous and crewless vehicles, and training and simulation systems.
- Life sciences industry- Common applications include proteomics, bioinformatics, and genome sequencing systems and devices
- Industrial automation industry- Embedded computing systems are used in different manufacturing systems.
These 25 recommendations should help you ace your upcoming embedded systems interview if well-rehearsed. Ensure that you take time to brainstorm excellent answers that can convince the interviewer that you are skilled when it comes to embedded systems.