Wake-up sources in ARM Architecture - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Wake-up Sources in ARM Architecture

Which of the following is NOT typically considered a wake-up source in ARM-based systems?

A CPU executing a NOP instruction

B Timer expiration event

C Power-on reset signal

D External interrupt from a GPIO pin

💡 Hint

Think about what triggers the CPU to leave a low-power state.

Wake-up sources are events that cause the CPU to exit a low-power or sleep mode. External interrupts, timers, and reset signals are common wake-up sources. Executing a NOP (no operation) instruction does not cause wake-up; it is just a CPU instruction that does nothing.

📋 Factual

intermediate

Common Wake-up Sources in ARM Systems

Which wake-up source is commonly used to periodically wake an ARM processor from sleep mode to perform tasks?

A Software interrupt

B External GPIO interrupt

C Watchdog timer expiration

D Brown-out detection

💡 Hint

This source is a timer that can reset or wake the system if it expires.

The watchdog timer is often used to wake the processor periodically to check system health or perform scheduled tasks. External GPIO interrupts can wake the system but are event-driven, not periodic. Software interrupts require the CPU to be active. Brown-out detection triggers on low voltage but is not periodic.

🔍 Analysis

advanced

Analyzing Wake-up Source Behavior

An ARM processor is in deep sleep mode. Which wake-up source will cause the CPU to resume execution immediately upon event detection?

A DMA transfer completion

B Software interrupt triggered by running code

C Cache miss event

D RTC alarm interrupt

💡 Hint

Consider which events can wake the CPU from deep sleep without CPU activity.

RTC (Real-Time Clock) alarm interrupts are hardware events that can wake the CPU from deep sleep immediately. Software interrupts require the CPU to be active to trigger. DMA transfer completion may not wake the CPU unless configured. Cache misses occur during CPU operation and cannot wake from deep sleep.

❓ Comparison

advanced

Comparing Wake-up Sources: External Interrupt vs Timer

Which statement correctly compares external interrupt wake-up and timer wake-up in ARM processors?

A External interrupts wake the CPU based on external signals; timers wake the CPU based on elapsed time.

B Timer wake-up is event-driven, while external interrupts are periodic.

C External interrupts can only wake the CPU if the timer is disabled.

D Both external interrupts and timers require software intervention to wake the CPU.

💡 Hint

Think about the source of the signal for each wake-up type.

External interrupts are triggered by signals from outside the processor, such as button presses. Timers wake the CPU after a set time period elapses. External interrupts are event-driven, not dependent on timers. Both can wake the CPU without software intervention if configured properly.

❓ Reasoning

expert

Determining Wake-up Source Impact on Power Consumption

In an ARM system designed for ultra-low power, which wake-up source choice minimizes overall power consumption during idle periods?

A Frequent external interrupts from noisy sensors

B Periodic timer wake-up with long intervals

C Continuous polling of input pins by software

D Software-triggered wake-up every few milliseconds

💡 Hint

Consider how often the CPU wakes and what causes unnecessary power use.

Periodic timer wake-up with long intervals allows the CPU to stay in low-power sleep longer, reducing power consumption. Frequent external interrupts or continuous polling cause the CPU to wake often, increasing power use. Software-triggered wake-ups require the CPU to be active, also increasing consumption.