In this article, we have listed Interview Questions and Answers for Embedded c developer Job opportunities. These Embedded c developer Interview Question Answers are divided into various categories which will help you crack Interviews and secure your job. All the categories and questions are listed below, click and explore the l/topic -
Interview Questions for Embedded c developer Categories:
1. Basic C Programming Questions:
Q1: What is the difference between C and Embedded C?
A:
C is a general-purpose programming language used for applications running on operating systems.
Embedded C is a subset of C optimized for programming microcontrollers and embedded systems, often requiring direct hardware interaction.
Q2: What is the difference between a macro and a function?
A:
Macro is defined using #define and perform inline code substitution at compile-time.
Function is compiled separately, supports type checking, and allows recursion.
Example:
#define SQUARE(x) (x * x) // Macro
int square(int x) { return x * x; } // Function
Q3: What is the difference between volatile and const in C?
A:
volatile: Prevents compiler optimizations, ensuring that a variable is always read from memory.
const: Specifies that a variable’s value cannot be modified after initialization.
Example:
volatile int sensor_value; // Value may change outside program scope
const int max_limit = 100; // Cannot be modified
Q4: What is the size of integer data types in Embedded C?
A: The size depends on the microcontroller and compiler, but typically:
Data Type | Size (8-bit MCU) | Size (32-bit MCU) |
char | 1 byte | 1 byte |
int | 2 bytes | 4 bytes |
long | 4 bytes | 4 bytes |
float | 4 bytes | 4 bytes |
Q5: What are function pointers? How are they used in Embedded C?
A: Function pointers store the address of a function and allow dynamic function calls. They are used in ISR (Interrupt Service Routines), callbacks, and state machines.
Example:
void (*ptr_func)(void); // Function pointer declaration
void LED_ON() { /* Turn LED ON */ }
ptr_func = &LED_ON; // Assign function address
ptr_func(); // Call function via pointer
Q6: What is the difference between malloc() and static memory allocation?
A:
malloc(): Allocates memory dynamically from the heap, requiring free() for deallocation. Not commonly used in embedded systems due to limited RAM.
Static allocation: Memory is allocated at compile-time and does not require manual deallocation.
Q7: What are the different storage classes in C?
A:
auto: Default local variable storage in stack.
static: Retains value across function calls.
register: Requests CPU register storage for faster access.
extern: Used for global variable sharing across files.
Example:
static int counter = 0; // Retains value across function calls
Q8: What is the role of volatile in embedded systems?
A:volatile ensures that the compiler does not optimize away a variable that may change outside the program's control (e.g., hardware registers, sensor values, ISR flags).
Example:
volatile int flag; // Prevents compiler optimization of flag updates
Q9: How do you write an ISR (Interrupt Service Routine) in Embedded C?
A:An ISR is a function executed when a specific interrupt occurs.
Example (AVR microcontroller):
#include <avr/interrupt.h>
ISR(TIMER1_OVF_vect) {
// Code to handle timer overflow interrupt
}
Key rules:
No return value
No arguments
Keep execution time minimal
Q10: How do you interface an LED with a microcontroller?
A:An LED is connected to a GPIO pin, and it is controlled using HIGH (ON) or LOW (OFF) signals.
Example:
#define LED_PIN 5
void setup() { DDRB |= (1 << LED_PIN); } // Set pin as output
void loop() { PORTB ^= (1 << LED_PIN); } // Toggle LED
Q11: What is I2C, and how does it work?
A: I2C (Inter-Integrated Circuit) is a two-wire protocol (SDA, SCL) used for communication between microcontrollers and peripherals. It operates in master-slave mode.
Example:
void I2C_Start() { /* Send START condition */ }
void I2C_Write(uint8_t data) { /* Send data over SDA */ }
uint8_t I2C_Read() { /* Read data from SDA */ }
Q12: What is the difference between polling and interrupts?
A:
Feature | Polling | Interrupts |
Execution | Constant CPU checking | Only executed when an event occurs |
Efficiency | Inefficient (wastes CPU cycles) | Efficient (CPU can do other tasks) |
Example | Checking button press in a loop | Handling button press via ISR |
Q13: What is the difference between task scheduling in RTOS and bare-metal programming?
A:
Bare-metal: Uses a super-loop structure; tasks are executed sequentially.
RTOS: Uses a scheduler to run multiple tasks concurrently based on priorities.
Example (FreeRTOS task creation):
void Task1(void *pvParameters) {
while(1) { /* Task code */ }
}
xTaskCreate(Task1, "Task1", 128, NULL, 1, NULL);
vTaskStartScheduler();
Q14: What are mutexes and semaphores in RTOS?
A:
Mutex: Prevents multiple tasks from accessing the same resource (e.g., UART).
Semaphore: Synchronizes tasks (e.g., a task waits for a signal from an ISR).
Example (Binary semaphore in FreeRTOS):
SemaphoreHandle_t xSemaphore;
xSemaphore = xSemaphoreCreateBinary();
if (xSemaphoreTake(xSemaphore, portMAX_DELAY)) { /* Critical section */ }
Q15: How do you debug an embedded C program?
A:
Using Debuggers (JTAG, SWD)
Using Serial Print Statements (UART/printf)
Using LED Debugging (Toggling LEDs at checkpoints)
Using Logic Analyzers and Oscilloscopes
Q16: How do you optimize an embedded C program for speed and memory?
A:
Use volatile for hardware registers.
Avoid dynamic memory allocation (malloc()).
Use bitwise operations instead of expensive arithmetic.
Use lookup tables for repetitive calculations.
Minimize function calls and inline functions where necessary.
Q17: What is endianness? How does it affect embedded programming?
A:
Little-endian: Least significant byte stored first (e.g., Intel).
Big-endian: Most significant byte stored first (e.g., Motorola).Effect: When sending data between different architectures, byte-order conversion may be needed.
Example:
uint32_t num = 0x12345678;
uint8_t ptr = (uint8_t)#
printf("%x %x %x %x", ptr[0], ptr[1], ptr[2], ptr[3]); // Little-endian output: 78 56 34 12
Q18: What is a watchdog timer (WDT)?
A:A WDT resets the system if it hangs. If the program doesn't reset the WDT periodically, it assumes a failure and restarts.
Example:
void watchdog_init() { WDTCR |= (1 << WDE); } // Enable watchdog
void reset_watchdog() { WDTCR |= (1 << WDRF); } // Reset WDT
Embedded C Interview Questions for Freshers:
1. What is embedded C programming language?
A.Embedded C is a version of the C programming language commonly used for programming microcontrollers and other small, low-power devices. It includes various specific extensions and modifications to the standard C programming language. It fulfills the requirements of embedded systems, such as limited memory and processing power, real-time constraints, and the need for an interface for hardware peripherals.
2. What do you mean by a void pointer in the embedded C programming language?
A.In an embedded C programming language, a void pointer can pass a pointer to a function without declaring the type of data it is pointing to. This allows flexibility in function calls and can be helpful in many situations where the data type may be determined dynamically at runtime.
3. What is the segmentation fault in embedded C programming?
A.A Segmentation fault can occur due to less memory and processing power compared to a desktop computer. For example, if a program uses all the available memory of a device, it may cause a segfault or segmentation fault when it tries to allocate more memory.
4. What is stack overflow error in embedded C programming?
A.A stack overflow error in embedded C programming occurs when too much memory is being used on the stack; overflow can happen into adjacent memory spaces. This can happen due to infinite recursion, large data structures placed on the stack, or excessive stack usage.
5. What do you understand about embedded systems?
A.Embedded systems are computer systems that are integrated into a larger device or system and are dedicated to performing specific tasks. They are designed to perform a limited number of functions and are meant to be used in a specific way.
6. What is the use of the “volatile” keyword in the embedded C programming language?
A.The volatile keyword in embedded C programming is used to indicate to the compiler that a variable might be modified by an external event, such as an interrupt service routine or hardware.
7. What is the use of the “const” keyword in the embedded C programming language?
A.The const keyword in embedded C programming is used to declare the constant value that cannot be modified during the execution of a program.
8. What is the use of static variables in embedded C programming?
A.In embedded C programming, a static variable is declared with the static keyword. A static variable is local to a function or file. It retains its value between invocations of the function or between different executions of the program.
9. What do you mean by ISR in embedded C programming?
A.In embedded C programming, ISR stands for Interrupt Service Routine. An ISR is a type of function that is executed in response to an interrupt. Interrupts are external events, such as a button press or a timer expiring, that temporarily stop the normal flow of program execution and cause the microcontroller to jump to the ISR.
10. Why do we need a bootloader in embedded C programming?
A.A bootloader is a small program that runs on an embedded system before the main program. It is responsible for initializing the hardware and loading the main program into memory.
Embedded C Interview Questions for Intermediate:
11. What are pre-decrement and post-decrement operators in embedded C programming?
A.In embedded C programming, the pre-decrement and post-decrement operators are used to decrement a value by 1.
The pre-decrement operator (--) decrements the value. It returns a new value before it is used in an expression.
Example:
int x = 9;
int y = --x; // x is now 8, y is 8
The post-decrement operator (--) returns the original value assigned while declaring a variable before it is decremented, and then the value is updated.
Example:
int x = 9;
int y = x--; // x is now 8, y is 9
Both of these operators are commonly used in control structures, for example, for loops and while loops to control the iteration of the loop.
12. What is a “null pointer” in embedded C programming?
A.In embedded C programming, a null pointer is a type of pointer that doesn't point to a valid memory location. In other words, it points to a location with a value of 0 and is used to represent an undefined or uninitialized memory location.
A null pointer is often used to indicate the end of a list. It is also used to show an error condition in a program. Accessing or dereferencing a null pointer is undefined behavior in embedded C. That can result in a runtime error, such as a segmentation fault or a null pointer exception, depending on the system and the programming environment.
To check if a pointer is a null pointer or not, you can use the following comparison in your code:
if (ptr == NULL) {
// handling null pointer
}
Handling null pointers properly is an essential aspect of embedded C programming, and can help to prevent unpredictable behavior and runtime errors in your program.
13. What are the advantages of embedded C programming?
A.Embedded C programming language has several advantages over other programming languages and approaches, mostly for embedded systems development.
Some of these advantages include
Embedded C programming is based on the widely-used C programming language. That makes it easier for many developers to learn and use than other embedded programming languages.
C is a portable programming language. That means code written in C can quickly transfer between different hardware platforms.
C is a low-level programming language that provides direct access to hardware resources. That makes it possible to write highly efficient code for embedded systems with less processing power and memory.
The embedded C programming language provides fine-grained control over memory allocation. It is essential in embedded systems where memory is limited.
14. What are the disadvantages of embedded C programming?
A.The embedded C programming language has some disadvantages that should be considered when deciding whether it is the best choice for a given embedded system or not.
Some of these disadvantages include
The embedded C programming language can be complex, especially for developers who are unfamiliar with low-level programming or hardware-specific concepts.
The embedded systems are safety-critical, and bugs or errors in the code can have serious consequences. The embedded C programming language can be error-prone, mainly when dealing with hardware-specific functions and real-time requirements.
Debugging embedded systems can be challenging, mainly when dealing with low-level hardware-specific functions and real-time constraints.
The embedded C programming language provides limited abstraction from the underlying hardware. That can make it more challenging to develop code that is portable and scalable.
15. What are the main reasons for segmentation faults in embedded C programming?
A.The segmentation fault is also known as a “segfault.” It is a common error in the embedded C programming language. It occurs when a program tries to access a memory address it is not authorized to access. Some of the main reasons for segmentation faults in embedded C programming language include
Overflowing the stack, which means writing data beyond the end of the stack memory allocated to a program, and it can result in a segmentation fault.
Overflowing a buffer, which means writing more data to a buffer than it can hold, and it can result in a segmentation fault if the excess data overwrites adjacent memory.
Using a pointer after it has been freed, which means accessing memory that has already been released, can result in a segmentation fault.
Using pointers that do not point to valid memory can result in a segmentation fault.
16. What do you mean by interrupt latency in embedded C programming?
A.Interrupt latency in embedded C programming language refers to the time it takes for a microcontroller to respond to an interrupt, from the moment it is triggered until the interrupt service routine (ISR) begins execution.
It is an important performance metric in embedded systems, as it affects the real-time behavior of the system. A high interrupt latency can cause the system to miss critical events or deadlines. Whereas a low interrupt latency helps to ensure that the system can respond quickly to events and conditions.
17. How can you control the interrupt latency in embedded C programming?
A.There are some factors that can affect interrupt latency in embedded systems including the complexity of the ISR, the interrupt priority, the microcontroller architecture, and the system load.
To minimize interrupt latency, embedded C programmers may use techniques such as optimizing the ISR, low-latency interrupt handling techniques, and selecting microcontrollers with low interrupt latency. It's essential to carefully measure and analyze interrupt latency to ensure that the system meets its real-time requirements.
18. What are the features of using the static variable in the embedded C programming language?
A.Static variables in the embedded C programming language can have the following features:
These variables maintain their value across the function calls and persist in memory until the end of the program.
These variables have global scope, which means they can be accessed from any function within the program.
These variables are automatically initialized to zero if no initial value is specified.
These variables are only visible within the file in which they are defined.
The lifetime of these variables is limited to the duration of the program.
These variables are stored in the memory data segment, which is not subject to automatic allocation and deallocation like the stack segment, resulting in reduced memory usage.
19. What do you mean by CISC in embedded C programming?
A.CISC stands for Complex Instruction Set Computing. It refers to a type of microprocessor architecture. These types of microprocessors have a large and complex instruction set. They can execute different instructions, including instructions that perform multiple operations in a single cycle.
In the embedded C programming language, CISC microprocessors are mainly used in applications that require a high degree of flexibility and performance, such as real-time systems, control systems, and signal processing systems. These microprocessors are designed to perform complex operations quickly and efficiently. They allow them to handle demanding workloads with ease.
20. What do you mean by RISC in embedded C programming?
A.RISC stands for Reduced Instruction Set Computing. It refers to a type of microprocessor architecture. These types of microprocessors have a smaller and simpler instruction set. They can execute fewer types of instructions than CISC (Complex Instruction Set Computing) microprocessors.
In the embedded C programming language, RISC microprocessors are mainly used in applications that require a high level of performance and power efficiency. For example, low-power devices, IoT (Internet of Things), and mobile devices. These microprocessors are designed to perform simple operations quickly and efficiently. They allow them to handle primary workloads with low power consumption.
Embedded C Interview Questions for Experienced:
21. Why do we need embedded systems?
A.Embedded systems are very important in today's world because they are used to control and monitor a wide range of different devices and systems. They are helpful in providing the necessary computing and control functions for products that range from consumer goods, such as smartphones and home appliances, to industrial systems, such as process control and medical equipment, etc.
Some specific reasons for the need for embedded systems include
They can perform real-time control and monitoring tasks that are essential in many applications where fast and reliable control is required.
They are often more cost-effective than general-purpose computer systems. They are designed specifically for a particular application and only have the components required to perform useful functions.
Many of the embedded systems are small and portable. That makes them ideal for use in a wide range of applications, including handheld devices and wearable technology.
They are designed to be energy efficient. That makes them ideal for use in applications where power consumption is much more important.
22. What are the differences between C programming and embedded C programming?
A.C programming language and embedded C programming language are similar in many ways. There are some critical differences between these two.
The C programming language is a general-purpose programming language, while embedded C programming language is a subset of C, i.e., designed explicitly for programming embedded systems.
The embedded C programming language must deal with some constraints, such as limited memory, processing power, and real-time requirements. On the other hand, the general C programming language is typically less constrained.
The embedded C programming language often requires hardware-specific features, such as interrupts and low-level I/O control. But these are not required in the general C programming language.
The embedded C programming language often uses libraries and frameworks that are specific to embedded systems. For example, real-time operating systems, device drivers, and low-level hardware abstraction layers, which are not used in the general C programming language.
The embedded C programming language requires code optimization to meet the constraints of embedded systems.
23. What do you mean by a dangling pointer in embedded C programming?
A.A dangling pointer in the embedded C programming language is a pointer that no longer points to a valid memory location. This can occur when a pointer is assigned to a particular memory location that has been freed or invalidated. If we attempt to access the data stored at the memory location pointed to by a dangling pointer can result in undefined behavior. For example, crashes, incorrect results, or memory corruption.
Dangling pointers can be caused by several issues, including improper memory management, bugs in the code, and race conditions. Suppose, if a pointer is assigned to the memory location of a dynamically allocated object, and that object is subsequently deleted or freed, then the pointer becomes a dangling pointer.
24. What do you mean by memory fragmentation in embedded C programming?
A.Memory fragmentation in embedded C programming refers to the situation where memory blocks in a system are divided into some smaller parts and are scattered in different locations, making it challenging to allocate large contiguous blocks of memory. It can happen when there is frequent allocation and deallocation of memory, leading to holes in the memory that can't be used for any new allocation requests. It can lead to performance degradation and reduced reliability in embedded systems.
Memory fragmentation in embedded systems is a common issue that can negatively impact the system's performance. When memory is dynamically allocated and deallocated, it can result in the creation of small, unused memory blocks scattered throughout the memory space. This can make it difficult to allocate a large contiguous memory block when needed, leading to performance degradation. In some cases, it can even give out-of-memory errors, causing the system to crash or behave in unexpected ways.
25. What do you understand by priority inheritance in embedded C programming?
A.Priority Inheritance is a crucial mechanism for real-time systems that need predictable execution times for their tasks. In such types of systems, tasks have assigned priorities, and a scheduler ensures that higher-priority tasks should be executed before the lower-priority tasks. However, when a lower-priority task holds a shared resource that a higher-priority task needs, the higher-priority task may be blocked, and it can cause a priority inversion. This can result in the higher-priority task taking longer than expected, leading to unpredictable system behavior.
To resolve this issue, the priority inheritance protocol temporarily raises the priority of the lower-priority task to the priority of the highest-priority task that is blocked on the resource. This ensures that the high-priority task can be completed promptly and reduces the risk of priority inversion. Once the high-priority task has released the resource, the priority of the lower-priority task is returned to its original value.
26. How can you handle errors and exceptional conditions in embedded systems?
A.Handling errors and exceptional conditions in embedded systems needs a proactive approach and a well-designed error-handling strategy. The following are some techniques for handling errors and exceptional conditions in embedded systems:
Return codes are a simple and effective way to report errors in embedded systems. Each function can return an error code to indicate whether it was completed successfully or if an error occurred.
Assertions checks that the system makes at runtime to ensure that the program is functioning as expected. If an assertion fails, the program can take appropriate action, such as stopping execution or triggering a debug breakpoint.
Logging is a helpful technique for recording information about errors and exceptional conditions. A Log can be stored in non-volatile memory and retrieved for analysis after an issue occurs.
Exception handling is a mechanism for dealing with unexpected or exceptional conditions in a structured way. Exceptions in embedded systems can be caught and handled using C++ try-catch blocks or similar constructs.
27. What considerations would you need to keep in mind when implementing a communication protocol in embedded C programming?
A.Implementing a communication protocol in embedded C programming requires understanding the protocol specifications and the system architecture. When implementing a communication protocol in embedded C programming, the following considerations should be considered:
Communication protocols have strict timing constraints, such as bit rate, clock stretching, and maximum rise and fall times. These constraints must be considered when implementing the protocol in embedded C.
The communication protocol must ensure that data is transferred reliably and accurately between the devices. This needs proper synchronization mechanisms, such as start and stop conditions, data packets, and error detection and correction mechanisms.
Interrupt handling is important in communication protocols, as it allows the system to respond quickly to incoming data. Interrupts must be handled in a timely and efficient manner, without compromising the performance of the system.
Communication protocols typically consume significant amounts of power, in low-power embedded systems. Consideration must be given to optimizing the power consumption of the protocol implementation.
28. How can you handle interrupt service routines in embedded systems and ensure they have predictable execution times?
A.Handling ISRs in embedded systems requires careful consideration of the system architecture and the design of the ISRs. The following are some ways for ensuring that ISRs have predictable execution times:
The ISR code should be kept as small and concise as possible, to minimize the amount of time spent in the ISR and to ensure that it can be executed quickly.
The priority of the ISRs should be set correctly so that critical ISRs are executed before less important ones. This ensures that critical operations are performed promptly, even in the presence of multiple ISRs.
Blocking operations, such as waits, semaphores, and locks, should be avoided in ISRs. They can cause unpredictable execution times and may lead to system deadlocks.
DMA(Direct Memory Access) can be used to transfer data to and from peripherals, offloading the processor and allowing the ISRs to return quickly.
Cooperative multitasking, also known as round-robin scheduling, can be used to ensure that each task, including ISRs, has a predictable amount of time to execute.
29. What are the differences between blocking and non-blocking I/O in embedded systems?
A.Blocking and non-blocking I/O are two approaches to input/output operations in embedded systems.
Blocking I/O refers to an I/O operation that blocks or waits for the operation to complete before the continuation of other tasks. This means that the system will be idle and unable to perform the other tasks until the I/O operation has been completed. For example, when reading from a blocking I/O device, the system will wait until all the data has been received before the continuation of other tasks.
Non-blocking I/O refers to an I/O operation that returns immediately, without waiting for the operation to complete. The system can continue to perform other tasks while the I/O operation is in progress without blocking. For example, when reading from a non-blocking I/O device, the system will start the read operation and return immediately. And allowing it to perform other tasks while the read operation is in progress.
30. How can you optimize your code performance and power consumption in embedded systems?
A.Optimizing code for performance and power consumption in embedded systems needs balancing of computational efficiency and energy efficiency. Here are some ways for optimizing code for performance and power consumption:
Choose efficient algorithms to minimize the number of instructions and memory accesses required to solve a problem. Avoid algorithms that are slow or require a large amount of memory.
Use data structures that are appropriate for the problem and minimize the number of memory accesses and operations required.
Use efficient instructions and avoid unnecessary operations. Shifting or rotating a register can slow down the system.
Minimize the number of iterations required by the loops and avoid using the nested loops, as they can slow down the system.
Minimize the time spent in interrupt service routines and avoid using blocking operations, such as waits, semaphores, and locks, in ISRs.
Frequently Asked Questions:
1.What are the challenges of Embedded C?
A.The hardware system is the only one supported by embedded C. Moreover, Embedded C has some scalability concerns. So it can not be scaled up. And various restrictions, such as memory restrictions or computer compatibility.
2.How is C and Embedded C different?
A.C is a general-purpose programming language, while Embedded C is a subset of C tailored for embedded systems. Embedded C focuses on low-level hardware interaction, optimization, and real-time constraints.
3.How to prepare for an Embedded C interview?
A.
Review C programming fundamentals.
Study embedded systems concepts.
Learn about microcontrollers and processors.
Practice coding for embedded applications.
Prepare for technical questions related to real-time operating systems and hardware interfacing.
Conclusion:
In this article, we have discussed embedded C interview questions. We have discussed interview questions in three categories: easy, medium, and hard. You can check out our other interview questions blogs on our site.
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