Real Hard Time
MontaVista's announcement was not met with universal approval. Both its most direct competitors, Utah-based Lineo and TimeSys Corporation had the following responses:
Through our acquisition and integration of Zentropix, Lineo has been delivering hard real-time Linux for more than a year now. We have real customers using our hard real-time solutions today in the areas of flight simulation, weather-monitoring systems, heart-monitoring systems, industrial controls and many others.
The Lineo real-time solution achieves guaranteed hard real-time microsecond response times today. This is very different from the “relatively fully preemptable kernel”, announced by this competitor.
Lineo continues to actively support and promote real-time technologies. For more information about Lineo's real-time technologies, please visit www.lineo.com/products/realtime_linux/index.html.
Lineo also makes hard real time available from our open-source site (opensource.lineo.com/projects.html). Users can download a full-version of RTAI (real-time application interface) and AtomicRTAI from this site.
At LinuxWorld in San Jose this year, Lineo announced it would integrate real-time technology into the Embedix SDK, which Lineo will ship in Q4 of this year.
A competitor of TimeSys recently announced that they are “the first to deliver hard real-time Linux”. TimeSys would like to point out that this statement is false based on the following facts:
TimeSys has delivered to the market in May 2000, our TimeSys Linux/RT product that incorporates direct extensions to the Linux kernel that provides a strong platform for building hard real-time applications. These kernel extensions included support for guaranteed and deadline-aware CPU reservations with enforcement, 256 levels of fixed-priority scheduling, support for priority inheritance, support for periodic tasks, and high-resolution clocks and timers. These Linux kernel extensions, called the “Resource Kernel (RK)” have been downloadable from our web site (www.timesys.com/products) since May 2000. RK extensions are binary-compatible with Linux by definition and can actually allow Linux applications to be given real-time and QoS guarantees without accessing or modifying the application source code.
It is well known in the real-time systems community that fixed-priority scheduling combined with priority inheritance support and high-resolution timers is sufficient to build hard real-time systems. In fact, the most popular framework for building hard real-time systems is called RMA (Rate-Monotonic Analysis), which requires only these primitives. RMA is the ONLY framework supported by all major standards in the real-time systems marketplace, including Real-Time Extensions to POSIX, Real-Time Java, Real-Time CORBA, Real-Time UML, Ada 83 and Ada95. The competition does not support QoS guarantees, priority inheritance, high-resolution timers or periodic tasks.
In addition, to the direct Linux kernel extensions described in (1) above, TimeSys Linux/RT 1.0 and 1.1 also includes the RTAI layer from DIAPM, Italy. The RTAI layer is an independent higher-priority real-time kernel that runs below Linux. TimeSys Linux/RT includes both this higher-performance (but non-Linux-binary-compatible RTAI) layer and the Resource Kernel extensions. The two are mutually exclusive, but both support hard real-time applications.
TimeSys Linux/RT capabilities are not hidden or abstract; they can be explicitly visualized by the use of the TimeTrace product from TimeSys (please see www.timesys.com/products). The exact sequence of scheduling events and system calls occurring on multiple TimeSys Linux/RT targets can be viewed on a host and verified for strict correctness. In fact, code segments and system calls that take less than tens of nanoseconds can be measured without adding any code to an application.