The technology
covered in this document is an enhanced version of Linux
to support real time requirements.
Linux is an open source operating
system loosely based on UNIX. It's sponsoring community
called the GNU Project, wanted to revolutionize software
development in the early 1990s by finding a way to subvert
intellectual property protection and make all software
source code freely available to anyone who wanted it.
Therefore, Linux was released using a license called
GPL, or GNU General Public License, who sole purpose
was to ensure that the software code remain readily
available, and all derived works must also openly provide
the code free of restrictions on ownership. This concept
is also called Copy-Left. Copy-Left uses copyrights
on the source of Linux, and a license agreement that
once accepted requires the licensee to distribute the
source code for the product and all derived works.
Knowing the GPL license terms are
important to understanding the commercialization of
Linux based technologies. Although a commercial entity
may charge a fee for a Linux (technically for distribution
costs), any changes to the source code must be included
with the license, and the full source of the Linux operating
system.
Many companies such as Red Hat license
a copy of Linux, but also bundle with it third party
products designed to make using the system easier. These
tools are not derived works, and thus not subject to
the GPL.
Another key to understanding GPL licensing
of Linux is that the system must be viewed as the kernel
(or key part of the operating system), derived works
on the kernel, and third party enhancements outside
the kernel. The first two items are covered by the GPL.
The latter is not. Many of the current Linux vendors
routinely modify the Linux kernel to provide enhancements,
primarily for hardware drivers. Others provide just
the generic Linux kernel, sometimes called the Vanilla
kernel
The kernel of Linux is still actively
enhanced by its founder, Linus Torvaldes, and dozens
of independent programmers. Their works are coordinated
through the Linux Foundation, which according to its
website, "is a nonprofit consortium dedicated to
fostering the growth of Linux - The Linux Foundation
promotes, protects and standardizes Linux by providing
unified resources and services needed for open source
to successfully compete with closed platforms."
Real Time Linux
According to the Real Time Linux Foundation,
Real Time Linux is an enhancement to the Linux Kernel
to support real-time computing, a software and hardware
design approach that requires that tasks be completed
within a set time frame, and that this time frame be
very short. Non real time operating systems don't care
if a task takes 1 second or 100 seconds. The performance
of the system is subject to hardware capabilities and
software integration. A real time operating system is
often required in embedded devices, and mission critical
applications such as defense, or safety.
At present the Real Time Linux Foundation
tracks 8 commercial real-time Linux companies, and 9
open source real time Linux communities. The commercial
companies generally provide their source code for the
real time enhancements, and view them as derivative
works of the Linux kernel subject to the GPL. The Real
Time Linux Foundation seeks to be "one entry point
into the world of real time Linux which offers a common
platform for discussion." They also offer yearly
conferences on the subject of Real Time Linux.
The most recent revelation is that
the latest version of vanilla Linux has just released
several enhancements to fully support real time processing.
They are turned off by default, but through configuration
can be activated. According to Mike Fulton, IBM's chief
real time architect, there is no reason to purchase
a separate real time extension for Linux. Mike leads
IBM's real time development group and the new trend
here now is building out java applications that run
on a real time Java Virtual Machine that then runs on
real time Linux. Real time Linux has become a commodity.
Potential Benefits of The Technology
RT Linux appears to be well suited
to a variety of more complex processors, high performance,
source code availability, and low cost.
It is used on more complex devices.
RT Linux version is superior
as it has a very small footprint, and superior performance.
