RTOS Advantages

Simple embedded systems typically use a Super-Loop concept where the application executes each function in a fixed order. Interrupt Service Routines (ISR) are used for time-critical program portions.
This approach is well suited for small systems but has limitations for more complex applications.

Disadvantages of the Super-Loop Concept

• Time-critical operations must be processed within interrupts (ISR)
  • ISR functions become complex and require long execution times
  • ISR nesting may create unpredictable execution time and stack requirements
• Data exchange between Super-Loop and ISR is via global shared variables
  • Application programmer must ensure data consistency
• A Super-Loop can be easily synchronized with the System timer, but:
  • If a system requires several different cycle times, it is hard to implement
  • Split of time-consuming functions that exceed Super-Loop cycle
  • Creates software overhead and application program is hard to understand
• Super-Loop applications become complex and therefore hard to extend
  • A simple change may have unpredictable side effects; such side effects are time consuming to analyze.

These disadvantages of the Super-Loop concept are solved by using a Real-Time Operating System (RTOS).

RTOS Concept

A RTOS separates the program functions into self-contained tasks and implements an on-demand scheduling of their execution.

An advanced RTOS, such as the Keil RTX, delivers serious benefits:

• Task scheduling - tasks are called when needed ensuring better program flow and event response
• Multitasking - task scheduling gives the illusion of executing a number of tasks simultaneously
• Deterministic behaviour - events and interrupts are handled within a defined time
• Shorter ISRs - enables more deterministic interrupt behaviour
• Inter-task communication - manages the sharing of data, memory, and hardware resources among multiple tasks
• Defined stack usage - each task is allocated a defined stack space, enabling predictable memory usage
• System management - allows you to focus on application development rather than resource management (housekeeping)

Tasks 1 & 2 are functions in the application. RTX provides management of the Memory Pool and Mailbox as well as the communication mechanisms used between the tasks.

RTX provides a simple syntax for straightforward access to all of the RTOS resources.