Watchdog reset recovery in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Watchdog Reset Cause Detection

What will be the output of this embedded C code snippet that checks the cause of the last reset?

Embedded C

#include <stdio.h>
#define WDT_RESET_FLAG 0x01
#define POWER_ON_RESET_FLAG 0x02

unsigned char reset_cause = WDT_RESET_FLAG;

int main() {
    if (reset_cause & WDT_RESET_FLAG) {
        printf("Watchdog Reset Detected\n");
    } else if (reset_cause & POWER_ON_RESET_FLAG) {
        printf("Power-On Reset Detected\n");
    } else {
        printf("Unknown Reset Cause\n");
    }
    return 0;
}

A Watchdog Reset Detected

B Power-On Reset Detected

C Unknown Reset Cause

D Compilation Error

💡 Hint

Check which reset flag is set in the reset_cause variable.

The reset_cause variable has the WDT_RESET_FLAG bit set, so the first if condition is true and prints "Watchdog Reset Detected".

🧠 Conceptual

intermediate

Purpose of Watchdog Reset Recovery Code

Why is it important to include watchdog reset recovery code in embedded systems?

A To increase the clock speed of the microcontroller

B To detect and handle system hangs by resetting the system safely

C To reduce power consumption during sleep mode

D To enable communication with external sensors

💡 Hint

Think about what a watchdog timer does when the system stops responding.

Watchdog reset recovery code helps detect when the system was reset due to a watchdog timeout and allows the program to handle this event safely.

🔧 Debug

advanced

Identify the Bug in Watchdog Reset Handling

What is the bug in this watchdog reset recovery code snippet?

Embedded C

void check_reset_cause() {
    if (reset_cause == WDT_RESET_FLAG) {
        // Handle watchdog reset
        reset_cause = 0;
    }
}

A The assignment operator '=' is used instead of comparison '==' in the if condition

B The reset_cause variable is not declared

C The reset_cause flag is cleared before handling the reset

D The function does not return a value

💡 Hint

Check the condition inside the if statement carefully.

Using '=' assigns WDT_RESET_FLAG to reset_cause instead of comparing it, causing incorrect behavior.

📝 Syntax

advanced

Correct Syntax for Clearing Watchdog Reset Flag

Which option correctly clears the watchdog reset flag in a hardware register named RESET_FLAGS?

Embedded C

/* Assume RESET_FLAGS is a hardware register where bit 0 is the watchdog reset flag */

A RESET_FLAGS == ~0x01;

B RESET_FLAGS = &~0x01;

C RESET_FLAGS |= 0x01;

D RESET_FLAGS &= ~0x01;

💡 Hint

To clear a bit, you use bitwise AND with the inverse mask.

Option D uses bitwise AND with the complement of 0x01 to clear bit 0 correctly.

🚀 Application

expert

Implement Watchdog Reset Recovery Logic

Given a microcontroller with a watchdog reset flag at bit 2 of the RESET_STATUS register, write the correct embedded C code snippet to detect a watchdog reset, clear the flag, and print "Recovered from watchdog reset".

A

if (RESET_STATUS & (1 << 2)) {
    RESET_STATUS |= (1 << 2);
    printf("Recovered from watchdog reset\n");
}

B

if (RESET_STATUS == (1 << 2)) {
    RESET_STATUS |= (1 << 2);
    printf("Recovered from watchdog reset\n");
}

C

if (RESET_STATUS & (1 << 2)) {
    RESET_STATUS &= ~(1 << 2);
    printf("Recovered from watchdog reset\n");
}

D

if (RESET_STATUS = (1 << 2)) {
    RESET_STATUS &= ~(1 << 2);
    printf("Recovered from watchdog reset\n");
}

💡 Hint

Use bitwise AND to check the flag and bitwise AND with complement to clear it.

Option C correctly checks if bit 2 is set, clears it by ANDing with the complement, and prints the message.