嵌入式软件开发面试题interview Questions for firmware engineer（2）

1.What is an embedded system, and how does it differ from a general-purpose computer?
-answer: NA

Can you explain the difference between microcontrollers and microprocessors?
-answer: NA

2.Programming Skills:

a. Which programming languages are commonly used in embedded systems development, and what are their advantages and disadvantages?
-answer: C programming language, and assembly language

b. How would you optimize code for memory-constrained environments in embedded systems?
answer:
. Enable compiler optimization flags,for size optimization.
. To minimize the use of constants, for example:

int a[10] = {
   0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // Initializes first 10 elements,

///use the below code instead to save flash.
int a[10];
for (i = 0 ; i < 20; i++)
{
   
   a[i] = i;
}

. Conditional Compilation (#ifdef, #ifndef)
. Minimize or avoid dynamic memory allocation (malloc, free) to prevent fragmentation
. Use static or stack-based memory allocation where possible.
. Store read-only data in flash memory rather than RAM when applicable.
. Consider using bit-fields for boolean flags to save space.
. Use data types that consume less memory when possible (e.g., uint8_t instead of int).

3.RTOS (Real-Time Operating System):

What is an RTOS, and when would you choose to use one in an embedded system?
-answer: NA

Can you name some popular RTOSs, and what factors would you consider when selecting one for a project?
-answer:
. FreeRTOS
real-time operating system
. μC/OS
Real-time operating systems
. embOS
A real-time operating system developed by SEGGER Microcontroller. It is known for its small footprint and fast context switching.
. MQX
a real-time operating system (RTOS) developed by NXP.

4.Interrupt Handling:

Explain the concept of interrupts in embedded systems.
How would you prioritize and handle multiple interrupts in a system?
What is interrupt latency? How can you reduce it?
Interrupt latency is the time it takes to return from the interrupt service function after handling a given interrupt.

5.Communication Protocols:

Briefly describe common communication protocols used in embedded systems (e.g., SPI, I2C, UART,CAN,ZigBee, BLE, Wi-Fi)?
-answer:

SPI:
. Involves four signals: MISO (Master In Slave Out), MOSI (Master Out Slave In), SCLK (Serial Clock), and SS/CS (Slave Select/Chip Select).
. Typically used for short-distance communication within a circuit board.
. Supports high data transfer rates (typically 10 Mbps.).
. Used for communication with sensors, displays, memory devices, and other peripherals.s.

I2C :
.speed: 400khz,(fast mode)
. waveform diagram- refer to the picture below，
. hw- Actual values for pull-up resistance used: 2.2Kohms ，Typical values :2.2k to 10k ohms
. the max number of devices :128(7-bi adress bit.)) ,
. the data could be transmission only SCL is low, because the DATA transmission
. when SCL is high, indicates it is a START or STOP condition.
. Uses two wires: SDA (Serial Data) and SCL (Serial Clock).
. Supports multiple devices on the same bus with unique addresses.
. Suited for moderate-speed communication.
. Commonly used for connecting sensors, EEPROMs, and other low to moderate-speed peripheral

UART:
.Involves two signals: TX (Transmit) and RX (Receive).
.No clock signal; timing is agreed upon by both communicating devices.
.Well-suited for longer-distance communication.
.Used for communication between microcontrollers, modules, and devices such as .GPS receivers and Bluetooth modules.

CAN:
. Differential signaling for noise immunity.
. Supports multiple nodes on the same bus.
. Built for reliability in noisy environments.
. Commonly used in automotive systems, industrial automation, and other . applications requiring real-time communication.

CAN Bus Explained — A Simple Intro [2023] — CSS Electronics

ZigBee:
. Utilizes low power, making it suitable for battery-operated devices.
. Supports mesh networking, allowing devices to relay messages through the network.
. Typically used in applications like home automation, industrial control systems, and wireless sensor networks.

BLE:
. Optimized for intermittent data transmission, making it energy-efficient.
. Commonly used in applications like wearables, health devices, and IoT (Internet of Things) devices for short-range communication.

Wi-Fi:
. High data rates suitable for applications requiring fast and reliable data transfer.
. Longer communication range compared to Zigbee and BLE.
. Used for internet connectivity in embedded systems, smart devices, and applications where high bandwidth is essential.

. When would you choose one communication protocol over another, and what are the trade-offs?
Answer:
. Data Transfer Rate
-High Data: Rate-Wi-Fi,
-Low to Moderate Data Rate:Zigbee and BLE)
. Power Consumption
-low-power operation:Zigbee and BLE
-Higher Power: Wi-Fi
. Communication Range:
-short-range communication: Zigbee and BLE
-Longer Range:Wi-Fi
. Application Specifics:
-internet connectivity: Wi-Fi
. Cost

6.Memory Management:

How do you manage memory in embedded systems with limited resources?
Can you explain the difference between stack and heap memory?
Answer:
1.Heap:
.brief description:
-used for dynamic memory allocation during runtime, is suitable for managing dynamic data structures like arrays, linked lists, and objects,use the function OS_HEAP_malloc, OS_HEAP_free.

void HPTask(void) {
   
OS_U32* p;
while (1) {
   
p = (OS_U32*)OS_HEAP_malloc(4);
*p = 42;
OS_HEAP_free(p);
}
}

. advantage:
-Flexibility for managing variable-sized data structures.
-Efficient use of memory.
Considerations(risk):

• memory leak -embedded device fails to release dynamically allocated memory properly.
• memory fragmentation

2. stack:
. used for managing function calls and local variables.
-risk: stack overflow
. solution:
-Size Determination;
-Stack Overflow Protection and monitoring,
-long-duration test and stress test.
. Considerations:
-Limited flexibility

static OS_STACKPTR int Stack[128]; // Task stack
static OS_TASK TCB; // Task control block
static OS_SEMAPHORE Sema; // Semaphore
static OS_TIMER Timer; // Timer to emulate interrupt

static void Task(void) {
   
while(1) {
   
OS_SEMAPHORE_TakeBlocked(&Sema); // Wait for signaling of received data
printf("Task is processing data\n"); // Act on received data
}

...
OS_TASK_CREATE(&