Health monitoring and heartbeat in FreeRTOS - Step-by-Step Execution

Concept Flow - Health monitoring and heartbeat

Start System

↓

Task sends heartbeat

↓

Monitor receives heartbeat

↓

Check heartbeat timing

↓

Continue

The system starts, tasks send heartbeat signals regularly, the monitor checks if heartbeats arrive on time, continuing if OK or raising alert if missed.

Execution Sample

FreeRTOS

void TaskHeartbeat() {
  while(1) {
    SendHeartbeat();
    vTaskDelay(pdMS_TO_TICKS(1000));
  }
}

void MonitorHeartbeat() {
  if (HeartbeatMissed()) Alert();
}

A task sends a heartbeat every second; the monitor checks if any heartbeat is missed and triggers an alert.

Execution Table

Step	Action	Heartbeat Sent?	Heartbeat Received?	Monitor Check	Result
1	Task sends heartbeat	Yes	No	No check yet	Waiting for heartbeat
2	Monitor receives heartbeat	Yes	Yes	Check timing	Heartbeat OK
3	Task delays 1 second	No	Yes	No new heartbeat	Waiting
4	Monitor checks heartbeat timeout	No	Yes	Timeout not reached	Heartbeat OK
5	Task sends heartbeat	Yes	Yes	Check timing	Heartbeat OK
6	Task delay longer than expected	No	Yes	No new heartbeat	Waiting
7	Monitor checks heartbeat timeout	No	No	Timeout exceeded	Alert raised
8	System handles alert	No	No	Alert active	System recovery or reset

💡 Monitor stops normal operation after heartbeat timeout exceeded and alert is raised

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	After Step 7	Final
Heartbeat Sent	No	Yes	No	Yes	No	No
Heartbeat Received	No	Yes	Yes	Yes	No	No
Monitor Alert	No	No	No	No	Yes	Yes

Key Moments - 3 Insights

Why does the monitor raise an alert even though a heartbeat was received earlier?

Because the monitor checks if the heartbeat arrives within a timeout window. If the heartbeat is missed for too long (see Step 7), it raises an alert even if previous heartbeats were received (Step 2).

What happens if the task delays longer than expected between heartbeats?

The monitor will detect no new heartbeat within the timeout period (Step 6 and 7) and raise an alert, indicating a possible task failure.

Does the monitor check heartbeat immediately after each send?

No, the monitor checks periodically and compares the last received heartbeat time against the timeout, as shown in Steps 4 and 7.

Visual Quiz - 3 Questions

Look at the execution table, at which step does the monitor first raise an alert?

A Step 5

B Step 7

C Step 3

D Step 2

💡 Hint

Check the 'Result' column for when 'Alert raised' appears.

According to the variable tracker, what is the state of 'Heartbeat Received' after Step 7?

A Yes

B Unknown

C No

D Pending

💡 Hint

Look at the 'Heartbeat Received' row under 'After Step 7' column.

If the task sends heartbeat every 500ms instead of 1000ms, how would the monitor's alert timing change?

A Alert timing would be delayed

B Alert would never occur

C Alert would occur sooner

D No change in alert timing

💡 Hint

Faster heartbeats mean the monitor resets timeout more often, so alert happens later if missed.

Concept Snapshot

Health monitoring uses periodic heartbeat signals from tasks.
Monitor checks if heartbeats arrive within a timeout.
If missed, monitor raises an alert.
Heartbeat interval and timeout must be balanced.
This helps detect task or system failures early.

Full Transcript

In FreeRTOS health monitoring, tasks send heartbeat signals regularly to indicate they are alive. A monitor task listens for these heartbeats and checks if they arrive on time. If a heartbeat is missed beyond a set timeout, the monitor raises an alert to signal a problem. This process helps detect failures early. The execution table shows steps where heartbeats are sent, received, and checked. Variables track heartbeat status and alerts. Key moments clarify why alerts happen after missed heartbeats and how timing affects monitoring. The quiz tests understanding of alert timing and variable states. Overall, this system ensures tasks are running properly by watching their heartbeat signals.