Clock gating for power saving in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this clock gating simulation code?

Consider the following embedded C code simulating clock gating behavior. What will be printed when this code runs?

Embedded C

#include <stdio.h>

int main() {
    int clock_enabled = 0;
    int power_consumption = 100; // base power

    if (clock_enabled) {
        power_consumption += 50;
        printf("Clock is enabled. Power consumption: %d\n", power_consumption);
    } else {
        printf("Clock is gated. Power consumption: %d\n", power_consumption);
    }
    return 0;
}

A Clock is gated. Power consumption: 150

B Clock is enabled. Power consumption: 150

C Clock is gated. Power consumption: 100

D Clock is enabled. Power consumption: 100

💡 Hint

Check the value of clock_enabled and how it affects power consumption.

The variable clock_enabled is set to 0, so the clock is gated. The power consumption remains at the base value 100.

🧠 Conceptual

intermediate

Which statement best describes clock gating?

Choose the statement that correctly explains the purpose of clock gating in embedded systems.

A Clock gating duplicates the clock signal to multiple modules for synchronization.

B Clock gating disables the clock signal to unused modules to reduce power consumption.

C Clock gating permanently turns off the power supply to a module.

D Clock gating increases the clock frequency to improve performance.

💡 Hint

Think about how clock gating helps save power without turning off the entire module.

Clock gating saves power by stopping the clock signal to parts of a circuit that are not in use, reducing switching activity and power consumption.

🔧 Debug

advanced

Identify the error in this clock gating code snippet

What error will this embedded C code produce when compiled?

Embedded C

void clock_gate(int enable) {
    if enable {
        // Enable clock
    } else {
        // Disable clock
    }
}

int main() {
    clock_gate(1);
    return 0;
}

A SyntaxError: Missing parentheses in if statement

B TypeError: Invalid argument type for clock_gate

C RuntimeError: Infinite loop detected

D No error, code compiles and runs

💡 Hint

Check the syntax of the if statement in C.

In C, the condition in an if statement must be enclosed in parentheses. Missing parentheses cause a syntax error.

🚀 Application

advanced

How many clock gating states are possible in this code?

Given this code controlling clock gating for two modules, how many unique clock gating states can the system have?

Embedded C

typedef struct {
    int module1_clock;
    int module2_clock;
} ClockControl;

int main() {
    ClockControl cc = {0, 0};
    // module1_clock and module2_clock can be 0 (gated) or 1 (enabled)
    return 0;
}

A 4

B 3

C 2

D 1

💡 Hint

Each module clock can be either gated or enabled independently.

Each of the two modules can be in 2 states (gated or enabled), so total states = 2 * 2 = 4.

❓ Predict Output

expert

What is the output of this clock gating control function?

Analyze the following embedded C code that simulates clock gating control. What will be printed?

Embedded C

#include <stdio.h>

void clock_gate(int *clock, int enable) {
    *clock = enable ? 1 : 0;
}

int main() {
    int clock_signal = 0;
    clock_gate(&clock_signal, 1);
    clock_gate(&clock_signal, 0);
    if (clock_signal) {
        printf("Clock enabled\n");
    } else {
        printf("Clock gated\n");
    }
    return 0;
}

A Clock enabled

B Compilation error

C No output

D Clock gated

💡 Hint

Trace the changes to clock_signal after each function call.

The first call sets clock_signal to 1 (enabled), but the second call sets it back to 0 (gated). So the final output is "Clock gated".