Bare-metal vs RTOS execution model in Embedded C - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of bare-metal loop execution

Consider this bare-metal style embedded C code running on a microcontroller. What will be the output on the serial console?

Embedded C

#include <stdio.h>

int main() {
    int count = 0;
    while (count < 3) {
        printf("Tick %d\n", count);
        count++;
    }
    return 0;
}

A Tick 0\nTick 1\nTick 2\nTick 3\n

B Tick 1\nTick 2\nTick 3\n

C Tick 0\nTick 1\nTick 2\n

D No output, infinite loop

💡 Hint

Count starts at 0 and increments until it reaches 3, but loop stops before printing count 3.

The loop runs while count is less than 3, so it prints Tick 0, Tick 1, and Tick 2, then stops.

❓ Predict Output

intermediate

RTOS task scheduling output

Given this simplified RTOS task code, what is the output order on the console?

Embedded C

#include <stdio.h>
#include <unistd.h>

void task1() {
    printf("Task 1 start\n");
    sleep(1);
    printf("Task 1 end\n");
}

void task2() {
    printf("Task 2 start\n");
    sleep(1);
    printf("Task 2 end\n");
}

int main() {
    task1();
    task2();
    return 0;
}

A Task 1 start\nTask 2 start\nTask 1 end\nTask 2 end\n

B Task 1 start\nTask 1 end\nTask 2 start\nTask 2 end\n

C Task 2 start\nTask 2 end\nTask 1 start\nTask 1 end\n

D Task 1 start\nTask 2 start\nTask 2 end\nTask 1 end\n

💡 Hint

Tasks run one after another in this code, no real multitasking.

Since task1() runs fully before task2(), output is task1 start/end then task2 start/end.

🧠 Conceptual

advanced

Difference in execution models

Which statement best describes the difference between bare-metal and RTOS execution models?

A Bare-metal supports multitasking natively; RTOS runs only one task at a time.

B Bare-metal uses threads; RTOS uses only interrupts.

C Bare-metal requires an OS kernel; RTOS runs without any kernel.

D Bare-metal runs a single loop without preemption; RTOS supports multiple tasks with preemptive scheduling.

💡 Hint

Think about how tasks are managed and switched.

Bare-metal typically runs one main loop without task switching; RTOS allows multiple tasks with preemption.

🔧 Debug

advanced

Identify the RTOS scheduling bug

This RTOS task code is intended to print alternating messages from two tasks. What is the bug causing only one task to print repeatedly?

Embedded C

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

void* task1(void* arg) {
    while(1) {
        printf("Task 1 running\n");
        sleep(1);
    }
    return NULL;
}

void* task2(void* arg) {
    while(1) {
        printf("Task 2 running\n");
        sleep(1);
    }
    return NULL;
}

int main() {
    pthread_t t1, t2;
    pthread_create(&t1, NULL, task1, NULL);
    pthread_join(t1, NULL);
    pthread_create(&t2, NULL, task2, NULL);
    pthread_join(t2, NULL);
    return 0;
}

A The program blocks on pthread_join(t1), so task2 never runs.

B The sleep(1) calls cause the tasks to never yield CPU.

C The tasks lack a termination condition causing deadlock.

D pthread_create is called incorrectly without task priorities.

💡 Hint

Check what happens after pthread_join(t1) is called.

pthread_join(t1) waits for task1 to finish, blocking main thread and preventing task2 from running.

🚀 Application

expert

Choosing execution model for a real-time sensor system

You design a sensor system that must read data every 10ms and process it without delay. Which execution model is best and why?

A Bare-metal, because it has minimal overhead and predictable timing.

B RTOS, because it allows multitasking and dynamic memory allocation.

C Bare-metal, because it supports preemptive multitasking natively.

D RTOS, because it eliminates the need for interrupts.

💡 Hint

Consider timing predictability and overhead.

Bare-metal systems have minimal overhead and predictable timing, ideal for strict real-time sensor reading.