2. Real-time?
Real-time might, as the name implies, sometimes also be about timeliness (fast), but in
my humble opinion it's usually about determinism.
To be precise about event- and temporal determinism (event determinism
meaning that you know the state of the outputs with a given set of inputs; temporal
determinism meaning that you also know exactly the timing).
Coming back to real-time versus real fast - In case of an aircraft navigation
system deadlines are in the tens of milliseconds, while for an airline reservation system
the deadlines are at about 15 seconds.
The latter must be deterministic just like the former one, but does not need to
be so fast.
After thirty years of research there is still no universal methodology to create
real-time systems and that's why in real life real-time is defined as follows:”A real-time
system will pass a specified test suite.[2]” Let's stick to those wise words of Paul E.
McKenny for the time being.
From Getting real (time) about embedded GNU/Linux
7. RTLinux
• First real-time extension for Linux
• It was developed by Victor Yodaiken, Michael
Barabanov, Cort Dougan and others at the New
Mexico Institute of Mining and Technology
• patent covering：
o US-Patents 5,995,74 owned by FSMlabs
9. RTAI & Xenomai
•
The Xenomai project was launched in August 2001. In 2003 it merged with the
Real-Time Application Interface (RTAI) project to produce a production-grade
real-time free software platform for GNU/Linux called RTAI/fusion, on top of
Xenomai's abstract real-time operating system (RTOS) core. Eventually, the
RTAI/fusion effort became independent from RTAI in 2005 as the Xenomai
project
• RTAI
o Like Linux itself the RTAI software is a community effort.
o Only really actively maintained on x86
o May offer slightly better latencies than Xenomai
• Xenomai
o Initial goals: facilitate the porting of programs to GNU / Linux.
o Any number of RTOS personalities called “skins” can then be built over the
nucleus, providing their own specific interface to the applications, by
using the services of a single generic core to implement it
15. Reference
• Getting real (time) about embedded GNU/Linux
http://www.embedded.com/design/embedded/4204740/Gettingreal--time--about-embedded-GNU-Linux
http://blog.linux.org.tw/~jserv/archives/2011/02/_realtime_gnuli.html
• Embedded Linux system development course
http://free-electrons.com/doc/training/embedded-linux/slides.pdf
• RT nanokernel for Embedded Linux
http://people.debian.org.tw/~jserv/RT-nanokernel.pdf
• 共同筆記 - 作業系統設計與實做
http://cs001.cs.ccu.edu.tw/wiki/%E9%A6%96%E9%A0%81
• RTAI - Real Time Application Interface Official Website
https://www.rtai.org/
• Xenomai: Real-Time Framework for Linux
http://www.xenomai.org/
![Real-time?
Real-time might, as the name implies, sometimes also be about timeliness (fast), but in
my humble opinion it's usually about determinism.
To be precise about event- and temporal determinism (event determinism
meaning that you know the state of the outputs with a given set of inputs; temporal
determinism meaning that you also know exactly the timing).
Coming back to real-time versus real fast - In case of an aircraft navigation
system deadlines are in the tens of milliseconds, while for an airline reservation system
the deadlines are at about 15 seconds.
The latter must be deterministic just like the former one, but does not need to
be so fast.
After thirty years of research there is still no universal methodology to create
real-time systems and that's why in real life real-time is defined as follows:”A real-time
system will pass a specified test suite.[2]” Let's stick to those wise words of Paul E.
McKenny for the time being.
From Getting real (time) about embedded GNU/Linux](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)