📚 EMBEDDED C

🧠 What is Embedded C?

Embedded C is an extension of the C programming language tailored for embedded systems development — systems with limited hardware (memory, CPU) and tight real-time constraints. It's used to program microcontrollers like 8051, ARM, PIC, AVR, etc.

📅 When is Embedded C Used?

When you're writing software for microcontrollers or embedded devices.
During firmware development for products like automotive ECUs, IoT devices, washing machines, medical devices, etc.
Anytime performance, memory usage, and timing are critical.

🌍 Where is Embedded C Used?

Automotive ECUs (Engine Control Units, Body Control Modules)
Consumer electronics (TVs, Washing Machines, Microwaves)
Industrial automation
Healthcare devices
Aerospace control systems
Robotics and IoT systems

❓ Why Use Embedded C?

It's close to hardware, allowing precise control of registers, ports, timers, etc.
Portable across different microcontrollers (with proper abstraction).
Efficient for real-time applications where timing and performance matter.
Supported by almost all embedded toolchains and compilers (e.g., Keil, IAR, MPLAB, STM32CubeIDE).

⚙️ How Do We Use Embedded C?

Write your C code using microcontroller-specific register definitions, memory-mapped I/O, and ISR functions.
Use predefined headers and drivers provided by microcontroller vendors.
Build and compile the code using a suitable IDE or toolchain.
Flash the binary to the target microcontroller.

Example (for an 8051):

#include <reg51.h>

void main() {
  while(1) {
    P1 = 0xFF;  // Set all pins on port 1
  }
}

🌟 Benefits of Embedded C

🔹 Efficient execution in resource-constrained environments
🔹 Precise control of hardware
🔹 Portable with minimal changes
🔹 Easy to maintain and modular
🔹 Structured programming for better development practices
🔹 Strong community support and vast legacy code

Interview Questions and Answers for Embedded C

🔧 Embedded C – Interview Questions & Answers

1. What is Embedded C?
Embedded C is a set of language extensions for the C Programming Language to support embedded processors and microcontrollers.

2. How is Embedded C different from C?
Embedded C includes direct access to hardware through memory-mapped I/O and register manipulation, unlike standard C.

3. What are the key features of Embedded C?
Portability, efficiency, low-level access, hardware interfacing, and deterministic execution.

4. What are microcontrollers?
Microcontrollers are small computing systems on a chip that control embedded devices.

5. What is the use of volatile keyword?
It tells the compiler that a variable can change at any time, preventing optimization that could ignore changes.

6. What is an ISR?
Interrupt Service Routine – a function triggered when a hardware interrupt occurs.

7. How do you declare an ISR in Embedded C?
Using compiler-specific syntax. For 8051: void isr() interrupt 1.

8. What is the role of registers?
Registers are memory locations inside the microcontroller used for data storage and control.

9. What are the data types commonly used?
int, char, unsigned, float, uint8_t, uint16_t, etc.

10. What is memory-mapped I/O?
Peripheral devices are assigned specific memory addresses that can be accessed like regular variables.

11. How do you turn on an LED in Embedded C?

P1 = 0x01; // Turns on LED connected to P1.0

12. What is bit manipulation?
Directly modifying bits for controlling specific hardware features.

13. Explain sbit keyword.
Used to access individual bits of a special function register.

14. What is a watchdog timer?
A hardware timer that resets the system if the software becomes unresponsive.

15. What is polling?
Continuously checking the status of a peripheral or flag.

16. What is debouncing?
Filtering the noise when reading mechanical switch input.

17. What is the stack used for?
Storing return addresses, local variables, and function parameters.

18. What is the heap used for?
Dynamic memory allocation (though it's avoided in embedded systems).

19. What are the memory sections?
Code, data, bss, stack, and heap.

20. What is the difference between const and #define?
const defines typed variables, #define is preprocessor macro substitution.

21. What is a real-time system?
A system where response time is critical, and tasks must execute within deadlines.

22. What is a timer in embedded systems?
A counter used for time tracking or generating delays.

23. How to generate delay in Embedded C?
Using timers or loops, e.g. for(i=0;i<50000;i++);.

24. What is the difference between a microprocessor and microcontroller?
Microcontroller has CPU, memory, and I/O on one chip; microprocessor only has CPU.

25. What is I2C?
A serial protocol for multi-device communication using 2 wires.

26. What is SPI?
Serial Peripheral Interface, a fast communication protocol using 4 wires.

27. What is UART?
Universal Asynchronous Receiver/Transmitter – used for serial communication.

28. What is GPIO?
General-Purpose Input/Output – pins used to control or read digital signals.

29. What is the purpose of static keyword?
Restricts variable scope to file or function.

30. What is inline assembly in Embedded C?
Embedding assembly code in C for performance-critical tasks.

31. What is typedef?
Used to define new names for data types.

32. What is the purpose of extern?
Declares a variable defined elsewhere in another file.

33. How do interrupts work in Embedded C?
Triggered by hardware, ISR is called to handle the event.

34. What is the difference between =, ==, and === in Embedded C?
= assigns, == compares; === doesn’t exist in C.

35. What is firmware?
Software programmed into non-volatile memory of embedded systems.

36. What are linker scripts?
Used to define memory layout and placement of code/data.

37. How to optimize embedded code?
Avoid floating-point, reduce recursion, minimize memory, use efficient algorithms.

38. What is the difference between call and goto?
call invokes a function with return, goto jumps unconditionally.

39. What is bootloader?
A small program that loads main firmware into memory during startup.

40. What is RTOS?
Real-Time Operating System used in complex embedded systems.

41. What is context switching?
Changing the CPU from one task/process to another.

42. What is DMA?
Direct Memory Access allows peripherals to transfer data without CPU.

43. What are software debuggers?
Tools to trace, inspect, and control code execution (e.g., Keil, MPLAB).

44. What are common IDEs for Embedded C?
Keil uVision, MPLAB X, STM32CubeIDE, Code Composer Studio.

45. What is code profiling?
Analyzing code performance and identifying bottlenecks.

46. What are volatile vs const volatile?
volatile: variable may change unexpectedly; const volatile: can change, but not modified in code.

47. What is memory leak in embedded systems?
Failure to free unused memory — dangerous due to limited resources.

48. What is the role of linker and compiler?
Compiler converts code to object file; linker combines into a final executable.

49. What is endianess?
Byte order — Little Endian (LSB first) or Big Endian (MSB first).

50. How to ensure safety in embedded development?
Follow MISRA C, use static analysis, test rigorously, use watchdogs.