Bare Metal Programming vs RTOS

Bare-Metal Programming vs RTOS

1. What is Bare-Metal Programming?

• Bare-metal programming means writing code that runs directly on the hardware, without any operating system or OS-like abstraction.
• Programmer is responsible for:
  • Directly configuring hardware (registers, peripherals)
  • Writing the main loop, ISRs (interrupt service routines)
  • Managing timing, concurrency, scheduling

2. What is an RTOS?

• An RTOS (Real-Time Operating System) is a lightweight OS designed to provide deterministic scheduling, task management, and inter-task communication, with guaranteed response times for critical tasks.
• RTOS provides:
  • Task/thread management (scheduling, priorities)
  • Inter-task communication (queues, semaphores, mutexes)
  • Time management (delays, timeouts, timers)
  • Optional: device drivers, file systems, networking

3. Bare-Metal: Architecture & Code Structure

• main() or `while(1)` loop runs forever, sometimes with polling and interrupt-driven events.
• No threads, no context switching.
• Interrupts are used for time-critical or asynchronous tasks.
• Example (pseudo-C):

#include <stdint.h>
void main() {
    hardware_init();
    while (1) {
        read_sensors();
        control_actuators();
        if (check_event()) handle_event();
        // polling, delays, etc.
    }
}
// ISR for timer or input
void TIM_IRQHandler(void) {
    // Fast, critical code only
}

4. RTOS: Architecture & Code Structure

• Code divided into tasks (threads), each with its own stack.
• RTOS kernel schedules which task runs, based on priority/timing.
• Tasks block/sleep/wait on events—no need for polling loops.
• Example (FreeRTOS-style C):

void TaskA(void *pvParams) {
    while (1) {
        read_sensors();
        vTaskDelay(100); // Sleep for 100 ticks
    }
}

void TaskB(void *pvParams) {
    while (1) {
        if (xSemaphoreTake(xEventSem, portMAX_DELAY))
            handle_event();
    }
}

int main() {
    hardware_init();
    xTaskCreate(TaskA, "Sensor", 128, NULL, 2, NULL);
    xTaskCreate(TaskB, "Event", 128, NULL, 3, NULL);
    vTaskStartScheduler(); // Starts RTOS, never returns
}

5. Pros & Cons

6. When to Use Each

• Bare-Metal is best when:

  • Ultra-low-power, ultra-low-latency required
  • Tiny microcontrollers, cost-sensitive designs
  • Application is simple: one main loop, few peripherals

• RTOS is best when:

  • Many concurrent tasks (control, comms, UI)
  • Complex timing/multitasking requirements
  • Need for modularity, portability, scalability
  • Application needs networking, file systems, or dynamic scheduling

7. Hybrid: Superloop + Cooperative Tasks

• Some designs use a “superloop” with cooperative tasks (state machines), without pre-emptive RTOS.
• Can add libraries for scheduling, software timers, or messaging.