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Real-Time Operating system Scheduler for RISC Processors

RTKernel-RISC is a powerful real-time multitasking scheduler for 32-bit x86 embedded systems. RTKernel RISC is compact (about 16k code, 6k data), fast, and offers excellent real-time response times. All RTKernel-RISC threads run within a single program (single process, multi-threaded).


  • Compact - 16k code, 6k data
  • High Performance
  • Multi-threaded
  • Supports Coldfire, PowerPC, MPC5200, XScale, ARM
  • Compatible with RTOS-32 from On-Time Software

RTKernel-RISC Threads

An RTKernel-RISC thread is implemented as a 'C' function. A program can dynamically create threads using the appropriate kernel API calls. These threads are subsequently executed in parallel with the main thread and any other threads.

Each thread has its own stack, a priority between I and 64, and a task state. Several threads can be started executing the same code; however, each is allocated its own stack and thus its own local variables. All threads have access to the program's global data. Thus, shared code and shared data are inherently implemented by RTKernel-RISC.

Inter-Task Communication

RTKernel-RISC offers three different mechanisms for inter-task communication:

The Scheduler

RTKernel-RISC's scheduler is event-driven. It was developed specifically for real-time requirements and adheres to the following rules:


The application's interrupt handlers can suspend or activate threads. Interrupt handlers can be programmed completely in 'C' within the application. They can freely exchange signals or data with threads using semaphores or mailboxes. Semaphore or mailbox operations may then initiate a task switch, if required. Interrupts from any hardware can be processed.


RTKernel-RISC is delivered in two versions. The Standard Version is optimized for minimum size and best performance, while the Debug Version contains additional code for parameter and consistency checks at run-time. The Debug Version recognizes usage errors and issues corresponding error messages. Moreover, the Debug Version offers numerous debugging aids. For example, the current source code position of a thread can be displayed, all locked resources can be listed, or the CPU time requirements can be determined for each thread and interrupt handler. An especially powerful tool is the Kernel Tracer; it can log kernel and application events in real-time for off-line analysis.

As an additional aid to debugging, RTKernel-RISC (Debug and Standard Version) offers a number of informational functions. For example, a list of all threads, semaphores, or mailboxes can be displayed, or the state of a specific thread can be queried. Furthermore, RTKernel-RISC keeps statistics of the stack usage of all threads and interrupt handlers.

RTKernel-32 Compatibility

With a few exceptions Rtkernel-RISC is compatible with RTKernel-32. RTKernel-32 is part of the RTOS-32 development suite for protected mode X86. RTOS-32 has a large installed base and worldwide reputation for rock solid value and reliability.

Supplemental Modules

RTKernel-RISC is supplied with the following supplemental modules, always delivered in full source code:

Optional Modules

Tightly integrated versions of the EBSnet's IPv4/IPv6 network stack and ERTFS DOS compatible file system packages are available for RTKernel-RISC.

RTKernel RISC offers excellent performance. It comes with a benchmark program that may be used to measure its performance on any computer. The table to the right gives some results for four typical X86 based target computers and for a 24 MHz MPC860 processor.

Note: Times are given in μs and times may vary due to instruction caching
43 5 0.73 15 Round-Robin task switch
79 10 1.61 20 Semaphore task switch
37 6 1.18 16 Semaphore Signal
25 4 1.24 14 Semaphore Wait
100 13 3.13 23 Task activation (Signal, Wait)
31 12 3.95 22 Store data in a mailbox
30 10 2.77 20 Retrieve data from a mailbox
96 12 2.50 22 Task-to-task communication
107 18 4.03 38 Task-to-mailbox-to-task-communication
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