Task states (Ready, Running, Blocked, Suspended) in FreeRTOS - Step-by-Step Execution

Concept Flow - Task states (Ready, Running, Blocked, Suspended)

Task Created

↓

Ready State

↓

Scheduler Picks Task

↓

Running State

↓

Blocked

↓

Ready

Tasks move between states: Ready means waiting to run, Running means executing, Blocked means waiting for event/time, Suspended means paused by user. Scheduler controls transitions.

Execution Sample

FreeRTOS

void vTaskFunction(void *pvParameters) {
  for(;;) {
    // Running
    vTaskDelay(1000); // Blocked
  }
}

A task runs, then calls vTaskDelay to block itself for 1000 ticks, then becomes ready again after delay.

Execution Table

Step	Task State	Action	Reason/Trigger	Next State
1	Ready	Scheduler selects task	Highest priority ready task	Running
2	Running	Task executes code	Normal execution	Running
3	Running	Calls vTaskDelay(1000)	Task requests delay	Blocked
4	Blocked	Delay timer counts down	Waiting for 1000 ticks	Blocked
5	Blocked	Delay expires	Timer reaches zero	Ready
6	Ready	Scheduler selects task again	Task is highest priority ready	Running
7	Running	Task resumes execution	After delay	Running

💡 Task cycles between Running, Blocked (delay), Ready states repeatedly as scheduler runs.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7
Task State	Ready	Blocked	Ready	Running
Delay Timer	0	1000	0	0

Key Moments - 3 Insights

Why does the task move from Running to Blocked after calling vTaskDelay?

Because vTaskDelay makes the task wait for a set time, so it cannot run until the delay expires (see execution_table step 3).

What is the difference between Ready and Running states?

Ready means the task can run but is waiting for the CPU; Running means the task is currently executing (see steps 1 and 2).

How does a Suspended state differ from Blocked?

Suspended is paused by user action and won't run until resumed; Blocked waits for events or time and resumes automatically (not shown in sample but important).

Visual Quiz - 3 Questions

Look at the execution_table, what is the task state immediately after calling vTaskDelay?

A Blocked

B Ready

C Running

D Suspended

💡 Hint

Check execution_table row 3 where vTaskDelay is called and state changes.

At which step does the task become Ready again after being Blocked?

A Step 4

B Step 6

C Step 5

D Step 7

💡 Hint

Look for when the delay expires and task moves from Blocked to Ready in execution_table.

If the task never called vTaskDelay, which states would it cycle through?

A Running and Blocked only

B Ready and Running only

C Blocked and Suspended only

D Suspended and Ready only

💡 Hint

Refer to variable_tracker and execution_table showing delay causes Blocked state.

Concept Snapshot

Task states in FreeRTOS:
- Ready: waiting to run
- Running: currently executing
- Blocked: waiting for event/time
- Suspended: paused by user
Scheduler moves tasks between these states based on events and priorities.

Full Transcript

In FreeRTOS, tasks move through states: Ready means the task is waiting to run; Running means it is executing on the CPU. When a task calls vTaskDelay, it moves to Blocked state, waiting for the delay to expire. After the delay, it returns to Ready, waiting for the scheduler to run it again. Suspended state is when the task is paused by user action and won't run until resumed. The scheduler controls these transitions based on priorities and events.