RTX Real-Time Operating System

The Keil RTX is a royalty-free, deterministic Real-Time Operating System designed for ARM and Cortex-M devices. It allows you to create programs that simultaneously perform multiple functions and helps to create applications which are better structured and more easily maintained.

Product Highlights

  • Royalty-free, deterministic RTOS with source code
  • Flexible Scheduling: round-robin, pre-emptive, and collaborative
  • High-Speed real-time operation with low interrupt latency
  • Small footprint for resource constrained systems
  • Unlimited number of tasks each with 254 priority levels
  • Unlimited number of mailboxes, semaphores, mutex, and timers
  • Support for multithreading and thread-safe operation
  • Kernel aware debug support in MDK-ARM
  • Dialog-based setup using µVision Configuration Wizard

While it is certainly possible to create real-time programs without an RTOS (by executing one or more functions in a Super-loop), there are numerous scheduling, maintenance, and timing issues that an RTOS like the Keil RTX solves for you. For a more detailed comparison between RTOS and Super-loop, take a look at the advantages of using an RTOS.


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Round-Robin yes
Preemptive yes
Cooperative yes
Task Specifications
Defined Tasks (max) Unlimited
Active Tasks 250
Defined Tasks (max) Unlimited
User Priorities 1 - 254
Stack Checking yes
Context Switch Time < 300 cycles
Interrupt Lock-Out Time -
Timeouts yes
Intervals yes
User Timers Unlimited
Signals/Events 16 per task
Inter-Task Communication
Events (max) Unlimited
Signals/Events 16 per task
Semaphores (max) Unlimited
Mutexes (max) Unlimited
Mailboxes (max) Unlimited
Maillbox size Unlimited (Default 20)


  • Unlimited means that the RTX kernel does not impose any limitations on the number. However, the available system memory resources limit the number of items you can create.
  • The RTX library for Cortex™-M3/M4 does not disable interrupts. Interrupt latency is the same as without the RTX kernel. Interrupt latency for Cortex™-M0/M1 is < 20 cycles.


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