Wake-up sources configuration in Embedded C - Mini Project: Build & Apply

Wake-up Sources Configuration

📖 Scenario: You are working on a small embedded system that can wake up from sleep mode using different sources like a timer, a button press, or a sensor signal.To save power, the system should only wake up from the sources you enable.

🎯 Goal: You will write a simple program to configure which wake-up sources are enabled using a bitmask variable.This will help the system know which events should wake it up.

📋 What You'll Learn

Create a variable to hold the wake-up sources configuration.

Define constants for each wake-up source using bit flags.

Set a configuration variable to enable specific wake-up sources using bitwise OR.

Print the final configuration value.

💡 Why This Matters

🌍 Real World

Embedded devices often need to save power by sleeping and waking only on certain events. Configuring wake-up sources correctly is essential for battery life and responsiveness.

💼 Career

Understanding bitwise operations and hardware configuration is key for embedded systems engineers and firmware developers working on low-power devices.

1

Define wake-up source constants

Define three constants called WAKEUP_TIMER, WAKEUP_BUTTON, and WAKEUP_SENSOR with values 0x01, 0x02, and 0x04 respectively.

Embedded C

// Define wake-up source constants here
// Your code here

Hint

Use #define to create constants with the exact names and values.

2

Create wake-up configuration variable

Create an unsigned char variable called wakeup_config and initialize it to zero.

Embedded C

#include 

#define WAKEUP_TIMER 0x01
#define WAKEUP_BUTTON 0x02
#define WAKEUP_SENSOR 0x04

// Create wakeup_config variable and set to 0
// Your code here

Hint

Use unsigned char wakeup_config = 0; to create the variable.

3

Enable timer and button wake-up sources

Set wakeup_config to enable both WAKEUP_TIMER and WAKEUP_BUTTON using the bitwise OR operator.

Embedded C

#include 

#define WAKEUP_TIMER 0x01
#define WAKEUP_BUTTON 0x02
#define WAKEUP_SENSOR 0x04

unsigned char wakeup_config = 0;

// Enable WAKEUP_TIMER and WAKEUP_BUTTON in wakeup_config
// Your code here

Hint

Use | to combine the flags.

4

Print the wake-up configuration

Write a printf statement to print the value of wakeup_config as a hexadecimal number with 0x prefix.

Embedded C

#include 

#define WAKEUP_TIMER 0x01
#define WAKEUP_BUTTON 0x02
#define WAKEUP_SENSOR 0x04

unsigned char wakeup_config = 0;

wakeup_config = WAKEUP_TIMER | WAKEUP_BUTTON;

// Print wakeup_config in hex format
// Your code here

Hint

Use printf("Wake-up configuration: 0x%02X\n", wakeup_config); to print the value.

Practice

1. Which of the following is a common wake-up source in embedded C devices?

easy

A. GPIO pin interrupt

B. Floating point calculation

C. String concatenation

D. File system read

Solution

1. Step 1: Understand wake-up sources

   Wake-up sources are hardware events that can wake a device from sleep mode, such as GPIO interrupts or timers.

2. Step 2: Identify valid wake-up sources

   GPIO pin interrupts are commonly used as wake-up sources because they detect external signals.

3. Final Answer:

   GPIO pin interrupt -> Option A

4. Quick Check:

   Wake-up source = GPIO pin interrupt [OK]

Hint: Wake-up sources are hardware events like GPIO or timers [OK]

Common Mistakes:

• Confusing software operations with hardware wake-up sources
• Thinking file operations can wake embedded devices
• Assuming calculations can trigger wake-up

2. Which syntax correctly enables a GPIO pin as a wake-up source in embedded C?

easy

A. enable_wakeup(GPIO_PIN_5);

B. GPIO_WAKEUP_ENABLE(5);

C. wakeup_enable(GPIO5);

D. set_wakeup_pin(5);

Solution

1. Step 1: Recognize common embedded C macros

   Macros often use uppercase and underscores, like GPIO_WAKEUP_ENABLE(pin).

2. Step 2: Match syntax style

   GPIO_WAKEUP_ENABLE(5); matches typical embedded C macro style for enabling wake-up on GPIO pin 5.

3. Final Answer:

   GPIO_WAKEUP_ENABLE(5); -> Option B

4. Quick Check:

   Macro style = GPIO_WAKEUP_ENABLE(5) [OK]

Hint: Look for uppercase macro style for hardware config [OK]

Common Mistakes:

• Using lowercase function names not defined in embedded C
• Confusing parameter formats
• Missing parentheses or semicolons

3. What will be the output of the following code snippet?

void configure_wakeup() {
    WAKEUP_ENABLE_TIMER(1000); // 1000 ms
    WAKEUP_ENABLE_GPIO(3);
}

int main() {
    configure_wakeup();
    if (is_wakeup_source(GPIO_3)) {
        printf("Wakeup by GPIO 3\n");
    } else if (is_wakeup_source(TIMER)) {
        printf("Wakeup by Timer\n");
    } else {
        printf("No wakeup source\n");
    }
    return 0;
}

medium

A. Wakeup by GPIO 3

B. Wakeup by Timer

C. No wakeup source

D. Compilation error

Solution

1. Step 1: Analyze function and macros usage

   The code uses WAKEUP_ENABLE_TIMER and WAKEUP_ENABLE_GPIO macros but does not define or include them, causing compilation errors.

2. Step 2: Check function calls and conditions

   Functions like is_wakeup_source and constants GPIO_3, TIMER are undefined, leading to compilation failure.

3. Final Answer:

   Compilation error -> Option D

4. Quick Check:

   Undefined macros/functions cause compilation error [OK]

Hint: Undefined macros or functions cause compile errors [OK]

Common Mistakes:

• Assuming macros are predefined without headers
• Ignoring missing function definitions
• Confusing runtime output with compile errors

4. Identify the error in this wake-up source configuration code:

void setup_wakeup() {
    WAKEUP_ENABLE_GPIO(2);
    WAKEUP_ENABLE_GPIO(2);
    WAKEUP_ENABLE_TIMER(500);
}

medium

A. Duplicate GPIO wake-up enable causes conflict

B. Timer value 500 is invalid

C. Missing return statement

D. No error, code is correct

Solution

1. Step 1: Review GPIO wake-up configuration

   The code enables GPIO pin 2 twice, which can cause conflicts or redundant configuration.

2. Step 2: Check timer configuration and function structure

   Timer value 500 ms is valid; no return needed for void function.

3. Final Answer:

   Duplicate GPIO wake-up enable causes conflict -> Option A

4. Quick Check:

   Duplicate GPIO enable = conflict [OK]

Hint: Avoid enabling same GPIO wake-up twice [OK]

Common Mistakes:

• Thinking timer value is invalid
• Expecting return in void function
• Ignoring duplicate hardware config issues

5. You want to configure a device to wake up either by GPIO pin 4 or after 2 seconds using a timer. Which code snippet correctly sets both wake-up sources?

hard

A. WAKEUP_CONFIG(GPIO4 | TIMER_2S);

B. WAKEUP_ENABLE_TIMER(2);
WAKEUP_ENABLE_GPIO(4);

C. WAKEUP_ENABLE_GPIO(4);
WAKEUP_ENABLE_TIMER(2000);

D. WAKEUP_ENABLE_GPIO(4, 2000);

Solution

1. Step 1: Understand separate wake-up source configuration

   GPIO and timer wake-up sources are usually enabled with separate calls specifying pin and time in milliseconds.

2. Step 2: Evaluate options for correctness

   WAKEUP_ENABLE_GPIO(4); WAKEUP_ENABLE_TIMER(2000); correctly enables GPIO pin 4 and timer with 2000 ms (2 seconds). WAKEUP_ENABLE_TIMER(2); WAKEUP_ENABLE_GPIO(4); uses 2 (seconds) instead of milliseconds. WAKEUP_ENABLE_GPIO(4, 2000); incorrectly combines parameters. WAKEUP_CONFIG(GPIO4 | TIMER_2S); uses an undefined macro.

3. Final Answer:

   WAKEUP_ENABLE_GPIO(4); WAKEUP_ENABLE_TIMER(2000); -> Option C

4. Quick Check:

   Separate calls with correct units = WAKEUP_ENABLE_GPIO(4); WAKEUP_ENABLE_TIMER(2000); [OK]

Hint: Enable GPIO and timer separately with correct units [OK]

Common Mistakes:

• Using seconds instead of milliseconds for timer
• Combining GPIO and timer in one call
• Using undefined macros