Hello 👋🏽 guys, I learnt about real-time systems recently and felt like passing the knowledge on. I Hope you’ll learn too.

Real time computer or systems are systems where tasks and operations are carried out within a guaranteed period of time called deadline. The main keyword there is "guaranteed" because that’s one of the major things that differentiates regular computer systems from real-time systems.

In a regular computer system, time is important but not as critical as in real-time systems. A regular computer system can prioritize tasks based on some other factors apart from time, such as overall system throughput, latency, complexity, user input, etc.

In contrast, on a real-time system, tasks are prioritize based on their deadline (maximum allowed time for execution) and failure of the system to complete a given task within its deadline can have various catastrophic consequences such as overall system failure, system inefficiency, loss of funds, and even loss of lives.

Here are some classic examples of real-time systems:
1. Aircraft control system
2. Automated assembly line
3. Industrial control system

Above examples are all classified under hard real-time systems, which are systems where deadline must be met or catastrophic consequences would occur. On the other hand, there are soft real-time systems which have more flexibility in meeting their real-time constraints and may still function adequately even if some constraints are not met. An example of a soft real-time system is a video streaming application.

To illustrate the criticality of time in hard real-time systems, consider an aircraft control system, timing is critical, and the system must be able to respond quickly and predictably to events. For example, if the plane encounters turbulence, the control system must be able to adjust the control surfaces to keep the plane stable within a very short period. Real-time systems in aircraft control are designed to respond within milliseconds or even microseconds.

Because of this time importance, a real-time system is architected slightly differently with a variety of specialized components (hardware and software) and techniques to ensure that tasks are completed within their deadline.

Some of these components and techniques that enable real-time systems to perform tasks real fast are:

1. Real-time operating system

A real-time operating system (RTOS) is a specialized operating system designed for real-time applications. RTOS provides services optimized for real-time performance, such as real-time scheduling, task management, inter-process communication, and memory management. An example of this is RTLinux.

2. Real-time Scheduling

Real-time scheduling is a technique used to schedule tasks in a real-time system to ensure that they are completed within their specified deadline. Real-time scheduling algorithms prioritize tasks based on their criticality and deadline, ensuring that the most important tasks are completed first.

3. Interrupt Handling

Interrupts are signals that are generated by hardware devices to notify the system of an event. In a real-time system, interrupt handling is crucial to ensure that the system can respond quickly to events. Interrupt handlers are designed to run quickly and efficiently, and they may disable other interrupts during their execution to ensure that the critical task is completed.

4. Preemption

Preemption is a technique used to interrupt a lower-priority task to allow a higher-priority task to execute. In a real-time system, preemption is crucial to ensure that the system can respond quickly to events.

5. Hardware Support

Real-time systems may also use specialized hardware components, such as real-time clocks, timers, and dedicated processors for specific tasks. These hardware components are optimized for real-time performance and can handle tasks with strict timing requirements.

Real-time Programming Languages

Real-time programming languages are programming languages built to be used on real-time systems or to be used in developing apps and programs that run on real-time systems. These programming languages offer some special features to enable developers write predictable and efficient codes that meets the time constraints of the host real-time system.

Some of these features are:

1. Determinism

These languages prioritize predictable and consistent execution of programs which is critical in a real-time environment

2. Low-level access

These languages provide access to the underlying system’s hardware, allowing developers to write codes that interact with the hardwares.

3. Memory management

Real-time programming languages often provide memory management features that allow developers to manage memory more efficiently, reducing the risk of memory leaks and other memory-related issues.

4. Preemption and scheduling

Real-time programming languages also provide features for scheduling and preempting tasks. This allows developers to prioritize tasks, and ensure more critical tasks takes precedence in execution.

Some examples of real-time programming languages are: C/C++, Ada, and VHDL

In summary, regular computer systems can handle tasks in a specific period of time, but they are not optimized for real-time performance. Real-time systems are designed to handle tasks with strict timing constraints and prioritize predictability and responsiveness over throughput.

Programming on a real-time system should be done with much care, attention, and understanding as a single flaw can lead to a big loss. Thanks for reading ✌🏽✌🏽