Bare-metal vs RTOS execution model in Embedded C - Visual Side-by-Side Comparison

Concept Flow - Bare-metal vs RTOS execution model

Start

↓

Bare-metal

↓

Single main loop

↓

Tasks run one by one

↓

No preemption

↓

RTOS

↓

Multiple tasks

↓

Scheduler runs

↓

Tasks preempted & switched

↓

Concurrent task execution

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End

Shows the flow difference: Bare-metal runs one main loop with tasks sequentially, RTOS uses a scheduler to switch between tasks for concurrency.

Execution Sample

Embedded C

int main() {
  while(1) {
    task1();
    task2();
  }
  return 0;
}

// RTOS example
void task1() { /*...*/ }
void task2() { /*...*/ }

Bare-metal runs task1 and task2 one after another in an endless loop; RTOS runs tasks with a scheduler allowing task switching.

Execution Table

Step	Model	Action	Task Running	Scheduler Active	Notes
1	Bare-metal	Start main loop	None	No	System starts, no scheduler
2	Bare-metal	Run task1()	task1	No	task1 runs fully
3	Bare-metal	Run task2()	task2	No	task2 runs fully after task1
4	Bare-metal	Loop back	None	No	Repeat tasks sequentially
5	RTOS	Start scheduler	None	Yes	Scheduler begins managing tasks
6	RTOS	Run task1()	task1	Yes	task1 runs until preempted
7	RTOS	Preempt task1	task1	Yes	Scheduler switches tasks
8	RTOS	Run task2()	task2	Yes	task2 runs concurrently
9	RTOS	Switch back to task1	task1	Yes	Tasks switch repeatedly
10	RTOS	Continue scheduling	task1/task2	Yes	Concurrent multitasking
11	Exit	System runs indefinitely	N/A	N/A	No exit in embedded systems

💡 Embedded systems run indefinitely; no normal exit.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 6	After Step 8	Final
Task Running	None	task1	task2	task1	task2	task1/task2 switching
Scheduler Active	No	No	No	Yes	Yes	Yes

Key Moments - 3 Insights

Why does bare-metal run tasks one after another without switching?

Because bare-metal has no scheduler (see execution_table steps 2-4), tasks run fully before the next starts.

How does RTOS allow tasks to run seemingly at the same time?

RTOS uses a scheduler to preempt and switch tasks quickly (see execution_table steps 6-10), creating concurrency.

Does bare-metal system have a scheduler active at any point?

No, bare-metal systems do not have a scheduler (see variable_tracker Scheduler Active column at steps 2-4).

Visual Quiz - 3 Questions

Look at the execution_table at step 3, which task is running?

A task1

B None

C task2

D Scheduler

💡 Hint

Check the 'Task Running' column at step 3 in execution_table.

At which step does the scheduler become active in the RTOS model?

A Step 5

B Step 7

C Step 2

D Step 10

💡 Hint

Look at the 'Scheduler Active' column in execution_table.

If we remove the scheduler in RTOS, how would the 'Task Running' column change after step 6?

A Tasks would switch as usual

B Only task1 would run continuously

C Only task2 would run continuously

D No tasks would run

💡 Hint

Without scheduler (see variable_tracker), no preemption means task1 runs fully.

Concept Snapshot

Bare-metal: single main loop runs tasks sequentially with no switching.
RTOS: uses scheduler to switch tasks, enabling multitasking.
Bare-metal has no preemption; RTOS preempts tasks.
RTOS scheduler manages task timing and concurrency.
Embedded systems usually run indefinitely without exit.

Full Transcript

This visual execution compares bare-metal and RTOS execution models in embedded C. Bare-metal runs a single main loop executing tasks one after another without interruption. The execution table shows steps where task1 runs fully, then task2 runs fully, looping endlessly. The scheduler is inactive in bare-metal. In contrast, RTOS starts a scheduler that manages multiple tasks by preempting and switching between them rapidly. The execution table traces scheduler activation and task switching steps. Variable tracking shows which task runs and scheduler status at each step. Key moments clarify why bare-metal lacks task switching and how RTOS achieves concurrency. The quiz tests understanding of task running states and scheduler activation. The snapshot summarizes the main differences simply.