What is RTOS?

Initially driven by military demands for precision and rapid response in the mid-20th century, RTOS, or Real-time Operating System, describes hardware & software systems that are subject to a “real-time constraint”. In essence, RTOS is a strict task planner, which prioritizes and schedules different tasks based on urgency and predetermined rules.

Key features of RTOS:

• Deterministic: Guarantees response to events within a set time (low latency)
• Efficient resource use: Uses minimal CPU, memory, and power, ideal for embedded systems.
• Task scheduling: Manages multiple tasks, prioritizing based on urgency or rules
• Reliability & stability: Designed to run continuously without crashing over long periods

Some may argue that since all systems have a response time, all computer systems are real-time. So what are the differences between RTOS and general-purpose operating systems?

RTOS vs. General-Purpose OS

While every operating system inherently has response time, RTOS is distinctly characterized by minimal latency, critical for embedded systems and smart devices. RTOS focuses on prioritizing and executing one single task at a time, while general purpose systems are capable of handling multiple apps with visually appealing user interfaces simultaneously at the expense of battery life due to higher processing demands.

Take Wear OS for example. Wear OS requires stronger CPU and GPU while a specific RTOS designed for smartwatches can run in a smaller MCU, which consumes significantly less battery. 

On small devices like smartwatches, battery life is arguably the most important factor, besides notifications and health tracking features. The question is, is there any way that we can maintain the rich visual experience without compromising battery life? With the combination of RTOS and general-purpose OS, the answer is yes.

How can RTOS extend smartwatches’ battery life?

To prolong the time between charges, some smartwatch makers have utilized bigger battery sizes, which impacts wearability, comfort, and aesthetics, especially in the case of health tracking (when lightweight devices are preferred for comfort and ease of movement). This is where the RTOS solution comes in handy.

Specifically, not every calculation on smartwatches demands the processing power of the main CPU. An offload system that utilizes the RTOS mechanism can effectively take over routine, less intensive tasks, allowing the main CPU to remain dormant more frequently, thereby decreasing the amount of power the smartwatch consumes at a given time. Meanwhile, the transition from the main CPU to the offload system and vice versa can occur seamlessly under the hood, ensuring an uninterrupted and smooth user experience.

The next question is, what to offload?

Tasks ideal for offloading include, but are not limited to:

• Sensor / Algorithm
• Watchface
• Watch app (e.g. workout, alarm, reminder, music/audio player)
• Phone notifications
• Bootup animation
• Companion Bluetooth communication

The goal of integrating RTOS into smartwatches isn’t to replace powerful general-purpose OS completely, but rather to intelligently manage resources. By offloading simpler tasks to an RTOS-based system, smartwatch manufacturers can significantly extend battery life without compromising the user experience. Users continue to enjoy visually rich interactions during active use, while benefiting from extended battery life during periods of inactivity.

In conclusion, integrating RTOS with general-purpose systems offers a promising solution for overcoming battery limitations, enabling smartwatches to deliver both engaging user experiences and superior battery performance.