MiThOS-a real-time micro-kernel threads operating system

Abstract

MiThOS (Micro-kernel Threads Operating System)is an experimental operating system for embedded sys-tems. The system kernel is a first implementation of the POSIX "Minimal Real-Time Sgstem Profile". It is based on prior work of a library implementation of Pthreads (POSIX threads). The system is fully preemptive. It supports multi-threading within a single process environment with shared kernel and user space, i.e. real-time tasks are mapped onto POSIX threads. It exhibits remarkable timing predictability intended for hard real-time requirements. This is achieved b y a careful design of only f e w device drivers. The system has been implemented and tested on the SPARC V M E architecture. The system includes a fast contezt switching algorithm for the SPARC which outperforms the context switch under SunOS and matches the performance under Solaris. It supports selective enabling and disabling of hardware components (MMU, caches, etc.) since its sources are available. Furthermore, an implementation-defined extension of POSIX threads for deadline scheduling is presented. Overall, the system exhibits slightly faster performance than SunOS 4.x and is considerably more predictable in its timing behavior. Applications of the kernel range from evaluating the overhead of new language features in Ada 95 and its runtime system, verifying static timing predictions on a bare machine, to providing the operating system for small embedded system that require a high timing predictability.

Predictable threads for dynamic, hard real-time environments

“…If either SCHED_FIFO or SCHED_OTHER are used, threads waiting on condition variables or mutexes are awakened in priority order. An early version of the PThreads standard was used as the basis for MiThOS, a small kernel for multithreaded embedded applications [18]. MiThOS supports priority-based scheduling and extends PThreads by allowing the direct specification of start time, deadline, and period.…”

User-level threads on a general hardware interface

“…Spare register window handling has been dealt with quite extensively (e.g. Anderson et al, 1991;Liedtke 1993;Mueller et al, 1994). The Arena HWO uses the register file as a temporary context buffer.…”