Wake-up sources configuration in Embedded C - Step-by-Step Execution

Concept Flow - Wake-up sources configuration

Start system in low power mode

↓

Configure wake-up sources

↓

Enable interrupts or events

↓

System sleeps

↓

Wake-up event detected?

No→Continue sleeping

Yes↓

Exit low power mode

↓

Resume normal operation

The system configures which events can wake it up, then sleeps until one occurs, then resumes normal operation.

Execution Sample

Embedded C

void configure_wakeup() {
  enable_wakeup_pin();
  enable_wakeup_timer();
  enter_low_power_mode();
}

This code sets up pin and timer as wake-up sources, then puts the system to sleep.

Execution Table

Step	Action	Wake-up Pin Enabled	Wake-up Timer Enabled	System State
1	Start configuration	No	No	Active
2	Enable wake-up pin	Yes	No	Active
3	Enable wake-up timer	Yes	Yes	Active
4	Enter low power mode	Yes	Yes	Sleeping
5	Wake-up event detected (pin)	Yes	Yes	Wake-up triggered
6	Exit low power mode	Yes	Yes	Active

💡 Wake-up event detected, system exits low power mode and resumes operation

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 6
Wake-up Pin Enabled	No	Yes	Yes	Yes	Yes
Wake-up Timer Enabled	No	No	Yes	Yes	Yes
System State	Active	Active	Active	Sleeping	Active

Key Moments - 2 Insights

Why does the system stay in 'Sleeping' state after enabling wake-up sources?

Because enabling wake-up sources only prepares the system; it enters low power mode only after calling enter_low_power_mode() as shown in step 4.

What triggers the system to exit low power mode?

A wake-up event such as a pin change or timer interrupt triggers exit, as shown in step 5 where the system detects the event and wakes up.

Visual Quiz - 3 Questions

Look at the execution table, at which step does the system enter low power mode?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Check the 'System State' column for when it changes to 'Sleeping'

According to variable_tracker, what is the state of 'Wake-up Timer Enabled' after step 2?

A No

B Yes

C Unknown

D Sleeping

💡 Hint

Look at the 'Wake-up Timer Enabled' row under 'After Step 2' column

If the wake-up pin was not enabled at step 2, what would happen at step 5?

A System wakes up normally

B System stays sleeping

C System crashes

D System resets

💡 Hint

Wake-up event depends on enabled sources; see step 5 where pin event triggers wake-up only if enabled

Concept Snapshot

Wake-up sources configuration:
- Enable hardware sources (pins, timers) before sleep
- Call low power mode function to sleep
- System wakes on enabled event
- After wake-up, resume normal operation
- Proper setup avoids missed wake-ups

Full Transcript

This example shows how an embedded system configures wake-up sources like pins and timers before entering low power mode. The system starts active, enables the wake-up pin and timer, then enters sleep. It stays sleeping until a wake-up event occurs, such as a pin change. When the event happens, the system exits low power mode and resumes normal operation. Variables track which sources are enabled and the system state changes from active to sleeping and back. Key points include that enabling sources does not sleep the system immediately, and wake-up events depend on enabled sources. This trace helps beginners see step-by-step how wake-up configuration works in embedded C.