Memory usage monitoring in FreeRTOS - Step-by-Step Execution

Concept Flow - Memory usage monitoring

Start System

↓

Initialize Memory

↓

Allocate Memory

↓

Monitor Usage

↓

Check Threshold

↓

Alert

↓

Free Memory

↓

Repeat Monitoring

This flow shows how FreeRTOS monitors memory: system starts, memory is allocated, usage is checked, alerts trigger if limits exceeded, then memory is freed and monitoring repeats.

Execution Sample

FreeRTOS

size_t freeHeap = xPortGetFreeHeapSize();
if (freeHeap < threshold) {
  notifyLowMemory();
}
// Continue normal operation

This code checks the free heap memory and triggers a notification if it falls below a set threshold.

Execution Table

Step	Action	Free Heap Size (bytes)	Condition (freeHeap < threshold)	Result
1	System starts, heap initialized	10000	10000 < 2000 ?	False, continue
2	Allocate 3000 bytes	7000	7000 < 2000 ?	False, continue
3	Allocate 4000 bytes	3000	3000 < 2000 ?	False, continue
4	Allocate 1500 bytes	1500	1500 < 2000 ?	True, notify low memory
5	Free 1000 bytes	2500	2500 < 2000 ?	False, continue
6	Allocate 600 bytes	1900	1900 < 2000 ?	True, notify low memory
7	Free 900 bytes	2800	2800 < 2000 ?	False, continue
8	Monitoring cycle repeats	2800	2800 < 2000 ?	False, continue

💡 Monitoring continues indefinitely, alerts sent when free heap falls below threshold

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	Final
freeHeap	10000	7000	3000	1500	2500	1900	2800	2800

Key Moments - 3 Insights

Why does the system notify low memory at step 4 but not at step 3?

At step 3, freeHeap is 3000 which is not less than the threshold 2000, so no alert. At step 4, freeHeap drops to 1500 which is below threshold, triggering notification (see execution_table rows 3 and 4).

What happens if memory is freed after a low memory alert?

Freeing memory increases freeHeap above threshold, so subsequent checks do not trigger alerts (see step 5 and 7 in execution_table).

Does monitoring stop after a low memory alert?

No, monitoring continues indefinitely, checking memory repeatedly and alerting whenever freeHeap is below threshold (see exit_note and repeated steps).

Visual Quiz - 3 Questions

Look at the execution table, what is the freeHeap value at step 4?

A 3000

B 7000

C 1500

D 1900

💡 Hint

Check the 'Free Heap Size (bytes)' column at step 4 in the execution_table.

At which step does the condition freeHeap < threshold first become true?

A Step 3

B Step 4

C Step 6

D Step 2

💡 Hint

Look at the 'Condition' column in execution_table and find the first 'True' value.

If the threshold was lowered to 1000, at which step would the first low memory alert occur?

A No alert would occur

B Step 4

C Step 8

D Step 6

💡 Hint

Compare freeHeap values with new threshold 1000 in execution_table rows.

Concept Snapshot

Memory Usage Monitoring in FreeRTOS:
- Use xPortGetFreeHeapSize() to get free heap memory.
- Compare free heap with a threshold.
- If below threshold, trigger alert (e.g., notifyLowMemory()).
- Free memory when possible to recover.
- Repeat monitoring continuously to avoid memory exhaustion.

Full Transcript

This visual execution trace shows how FreeRTOS monitors memory usage. The system starts with a free heap of 10000 bytes. As memory is allocated, free heap decreases. Each step checks if free heap is below a threshold (2000 bytes). When it is, a low memory notification is triggered. Freeing memory increases free heap and stops alerts until it falls below threshold again. Monitoring repeats indefinitely to keep the system stable.