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I'm somewhat confused on the Linux kernel version numbers. I noticed that many Linux distributions do no use the latest Kernels, in fact I have seen a few using version 2.4. Is there a reason for this? Is there any differences between 2.4, 2.6, 3.2 apart from age? What are the security implications of using an older kernel?
Different kernels have different features and improvements the developers of a distribution take a look at features they are going to support then decide which kernel to use based on the most stable support of that kernel.
It is the decision of the distribution developer which one to use, and they would go with the one they felt comfortable with.
This is a feature of software development its like asking what Java 1.1 and Java 1.7 is and whats the difference is apart from age... the answer is many things.
Most kernels and software will also have a security patch schedule and it is up to the user to keep their systems patched and up to date if you do not then you invite security issues as they are never fixed.
between major releases (e.g. 2.4 and 2.6), new features are introduced and old features are deprecated, eventually making the kernel binary incompatible.
this is important if you depend on some kernel-module that is not part of the mainline kernel (e.g. it is proprietary and the original authors don't provide updated modules; or it is open source (but never made it into the kernel) and nobody is willing to spend time to migrate the code)
also a new major release might change the system behaviour significantly. i remember that when switching from 2.4 to 2.6, many people that needed low latency audio (that's my background, so forgive me) would stay with the old kernel, since the new scheduling algorithms performed worse in some situations.
I hope the below page would help us in understanding the linux version numbering system:
http://www.linfo.org/kernel_version_numbering.html
A snap from http://www.tldp.org/FAQ/Linux-FAQ/kernel.html#linux-versioning
Linux version numbers follow a longstanding tradition. Each version has three numbers, i.e., X.Y.Z. The "X" is only incremented when a really significant change happens, one that makes software written for one version no longer operate correctly on the other. This happens very rarely -- in Linux's history it has happened exactly once.
The "Y" tells you which development "series" you are in. A stable kernel will always have an even number in this position, while a development kernel will always have an odd number.
The "Z" specifies which exact version of the kernel you have, and it is incremented on every release.
There is a human-readable changelog for the Linux Kernel.
Some people take the attitude "if it works - don't change it". So, there are security implications of running an older kernel - but there's also the risk that upgrading may break something.
As kernels improve/change, they might break expectations that held on earlier versions. If a distribution becomes unstable because too many software breaks under the new version of the kernel, the developers might opt to use an earlier version until the software is able to handle the changes in the new kernel.
Typically a binary image may not be portable between kernels where the first or second part of the version number changes. So in order to upgrade from 2.4 to 2.6, a large proportion of libs and executables will need to be upgraded / recompiled too. This can be a particular problem if you use closed source applications/drivers.
Most Linux distributors will back port patches from newer kernel versions depending on the security impact / demand for additional functionality. If you're not able to upgrade your entire system at regular intervals, then you need to find a distribution which explicitly supports a long support cycle with a good history of back porting (e.g. RHEL, SuSE).
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in which area is c++ mostly used?
I started off with C in school, went to Java and now I primarily use the P's(Php, Perl, Python) so my exposure to the lower level languages have all but disappeared. I would like to get back into it but I can never justify using C over Perl or Python. What real-world apps are being built with these languages? Any suggestions if I want to dive back in, what can I do with C/C++ that I can't easily do with Perl/Python?
To borrow some text from the answer I had for another related question:
Device drivers in native code.
High performance floating point number crunching (i.e. SIMD).
Easy ability to interface with assembly language routines.
Manage memory manually for extended execution runs.
Most of my work has been C and C++. I studied computer engineering in school and worked with embedded devices. My Master's degree had an emphasis in graphics and visualization. One of our visualization apps was written in Python, but for the most part, graphics demands C/C++ for the speed. I now work with embedded devices running Windows Mobile and Windows CE - all C++, though you can do a lot with C#. I previously worked in simulations, which was all C++ code on the backend. C++ is still king for time-sensitive IO, embedded applications, graphics and simulations.
Basically, if you need tight control of timing, you go lower level. Or if you need light-weight (ie, small program size, small memory footprint)
Somewhat unscientifically I took a look on Sourceforge and the top twenty projects/language break-down is currently thus:
Java(43,199)
C++(34,313)
PHP(28,333)
C(26,711)
C#(12,298)
Python(12,222)
JavaScript(10,307)
Perl(8,931)
Unix Shell(3,618)
Delphi/Kylix(3,353)
Visual Basic(3,044)
Visual Basic .NET(2,513)
Assembly(2,283)
JSP(1,891)
Ruby(1,731)
PL/SQL(1,669)
Objective C(1,424)
ASP.NET(1,344)
Tcl(1,241)
ActionScript(1,164)
Perl + Python together still total less than C alone. I have no idea why Java is so high, I know of no single Java developer and have not seen a single Java project, but I am sure someone is using it! For probably the same reason, you are not seeing much C/C++, you are just not working in a domain where it figures highly. I work in embedded systems where C and C++ are ubiquitous and Python comes nowhere. Different languages are encountered to different extents in different worlds.
You ask what you can do with C/C++ that you cannot do easily with Perl/Python; well the answer is plenty, real-time embedded systems for one; but if that is not what you want/need to do, then there is no reason to. On the other hand I might ask the reverse; I'd use C++ for things you might use Python for, simply because for me it would be easier and quicker (than learning a new language and getting the tools working)
C/C++ can be, and is, used for nearly all "types" of programs.
There are some major advantages to C and C++:
Potentially better performance
Easier to build interoperable libraries, especially if working with libraries usable from multiple languages.
well the interpreters for your "P's" languages are most certainly written in c/c++. Most OS code is written in C/C++. On the application side, if you are into games, they are generally written in c/c++. Anything that needs high performance and or low memory is a good candidate.
I've used Gsoap, a c++ soap client implementation for a web service that got HUGE traffic.
Most desktop/console applications with a bias toward graphics rely heavily on C++. This includes CAD software and AAA video games, among other things.
Anyone knows good environment to program VHDL and simulate it (don't matter Xilinx or Altera) using Linux?
You're stuck with either vendors tools, which are spotty at best on Linux (though my experience with Alteras utilities are somewhat better than with ISE).
However, if all you want to do is run your testbed, not actually synthesize anything, ghdl will be of use.
As mentioned by Arpan (almost) every VHDL simulator is supported by Linux, but they are usually very expensive. Your best shot would be to use one of the following:
Altera DS Web edition (Linux support has just been added) which comes with a free version of ModelSim.
Symphony EDA Sonata 3.1 is available as a free version with limited support.
Xilinx ISE which comes with Xilinxs own simulator: ISim.
Just to add an update to this: Xilinx Vivado has now been released with Linux support for ubuntu/debian and (I believe) redhat/centos.
The software is free for a range of the smaller devices and more common IP cores and includes a mostly decent simulator that is integrated into the tools and is also free.
It has a pretty steep learning curve, as do most of these tools, but as far as software in this industry goes, they've really done a good job with it.
If you prefer open source tools, look into http://www.cliftonlabs.com/vhdl/savant.html - vhdl does not have too many options in the FOSS space currently. If you are opting for vendor tools, all vendors would do Linux version of their simulators. Modelsim is a personal favorite due to the easy-to-debug features that it sports.
For a coding environment, I usually use VIM with vhdl syntax checkers turned on. Sigasi apparently has a commercial IDE with fancy stuff as automatic code completion, on the fly syntax check etc.
Let us know if you have further questions.
Arpan
For coding vhdl, Emacs with vhdl-mode is a must. You can use advanced edition functions, view the structure of designs, manage architectures and configurations. You can setup for multiple simulators.
I use the modelsim from Altera's Quartus web edition. Beware if you use a 64 bits Linux, this version of modelsim is 32 bits only.
There is now QUCS (http://qucs.sourceforge.net/) as well. It is open source and based on FreeHDL.
It can be used to design and simulate circuits using a graphical interface. And it can also simulate VHDL. Although for this you must also design the circuit components on the graphical area.
This video shows it clearly:
https://www.youtube.com/watch?v=-RrQlzLsf18
I'm using the linux ppa on Debian Jessie and it works fine.
GHDL is a nice simulator for VHDL, and even works with some third-party libraries (for example, Xilinx UNISIMS).
If you combine it with gtkwave, you should have a full working VHDL simulator and waveform viewer.
GHDL also supports writing to .GHW waveforms, which are fantastic for small simulations, cause it does include (often) all of the signals on your design.
I've used them with standard RTL simulation, and also for post-synthesis simulation with Xilinx UNISIMs.
Both should be available in your Linux distro repository. If not, you can fetch them from:
GHDL: http://ghdl.free.fr/
GtkWave: http://gtkwave.sourceforge.net/
I'm doing a trade study for Ada development on Linux. Do you have any good compiler/OS recommendations?
So far, I've got GNAT from AdaCore running on CentOS 5.4, and I have license requests in for Rational Apex and Aonix ObjectAda.
This is a porting effort. The original codebase is Apex 3.0 on OSF1 4.0d.
Anything else I should be considering? Ideally, it would be a supported environment.
One issue you need to take into consideration is to determine to what degree your system that's being ported utilizes vendor-supplied packages to perform its function. What I've seen with older, large systems, especially Apex ones, is a propensity for the language gurus during its development time to have decided that vanilla Ada just wasn't good enough, and so tie into all these vendor-supplied packages. If that's what your system does right now, it's a strong argument for upgrading within the vendor and sticking with Apex (all other things being mostly equal).
Whenever I've done ports of such systems, if given the opportunity I've done my best to tear out all the vendor-supplied stuff--nine times out of ten replacing the vendor-specific stuff with vanilla Ada implementations worked just as well, and you no longer have to deal with the quirks of a compiler-specific package. Plus, you increase the portability and maintainability of the system, allowing it to better adapt to future changes.
There is always SPARK, but I believe its a specialized/subsetted version of the Ada language. You might want to contact SigAda or the Ada usenet group to see if there are any other ideas.
Honestly though, GNAT is a great tool set. You can use GNATBench, an Eclipse interface, or GPS, a light-weight GTK+ IDE, to interface with the GNAT tools.
Other compilers I am aware of are Green Hills AdaMULTI (for various RTOSes), and DDC-I's SCORE (also for various RTOSes)
Providers of certified compilers that support Linux (in addition to those listed in the question):
Irvine Compiler Corp.
OC Systems
RR Software
Sofcheck
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I didn't find any useful information about programming languages for real time systems. All I found was Real Time Systems and Programming Languages: Ada 95, Real-Time Java and Real-Time C/POSIX (some pdf here), which seems to talk about extensions of Java and C for real times systems (I don't have the book to read). Also, the book was published in 2001, and the information may be obsolete now.
So, I'm dubious whether these languages are used in real world applications, or if real time systems in the real world are made in other languages, like DSLs.
If the second option is true for you, what are the outstanding characteristics of the language you use?
I am an avionics software engineer.
I was able to participate in several development projects.
The languages I used in those projects are: C, C++, and Real-time Java.
C is great.
C++ is not so bad but C/C++ require strict coding standards for the safety considerations such as DO-178B.
I think Real-time Java is the way to go but I don't see many avionics applications, yet.
Korean jet trainer T-50 will have a mission computer running RT Java application serving HUD and MFD displays, and all of the mission critical functions.
The Real-Time Specification for Java now has several commercial-grade implementations:
Sun's JavaRTS
IBM's WebSphere Real-Time
Aonix PERC
aicas JamaicaVM
Apogee Aphelion
These products span the continuum from compilation to native code (Aonix) to J2ME (aicas, apogee), to full J2SE (Sun, IBM). Most, if not all, have seen deployments in small numbers of safety- or mission-critical systems, but momentum is building. Examples include Eglin AFB's space surveillance radar modernization and the US Navy's use of RTSJ in the DDG-1000/Zumwalt destroyer. Sun also claims deployment in the financial transaction processing domain.
If you are interested in RTSJ, I suggest Peter Dibble's Real-Time Platform Programming, or Professor Wellings' Concurrent and Real-Time Programming in Java.
On a related note, there is also work underway to provide a Safety-Critical profile for the Java programming language, built as a subset of RTSJ. Also, an expert group has formed to explore a Distributed RTSJ DRTSJ, but the work is stalled.
The book covers use of Ada 95, the Java Real-Time System and realtime POSIX extensions (programmed in C). None of these is directly a domain specific language.
Ada 95 is a programming language commonly used in the late 90s and (AFAIK) still widely used for realtime programming in defence and aerospace industries. There is at least one DSL built on top of Ada - SparkAda - which is a system of annotations which describe system characteristics to a program verification tool.
This interview of April 6, 2006 indicates some of the classes and virtual machine changes which make up the Java Real-Time System. It doesn't mention any domain specific language extensions. I haven't come across use of Java in real-time systems, but I haven't been looking at the sorts of systems where I'd expect to find it (I work in aerospace simulation, where it's C++, Fortran and occasionally Ada for real-time in-the-loop systems).
Realtime POSIX is a set of extensions to the POSIX operating system facilities. As OS extensions, they don't require anything specific in the language. That said, I can think of one C based DSL for describing embedded systems - SystemC - but I've no idea if it's also used to generate the embedded systems.
Not mentioned in the book is Matlab, which in the last few years has gone from a simulation tool to a model driven development system for realtime systems.
Matlab/Simulink is, in effect, a DSL for linear programming, state machines and algorithms. Matlab can generate C or HDL for realtime and embedded systems. It's very rare to see an avionics, EW or other defence industry real-time job advertised which doesn't require some Matlab experience. (I don't work for Matlab, but it's hard to over emphasis how ubiquitous it really is in the industry)
Real time applications can be made in almost any language. The environment (operating system, runtime and runtime libraries) must however be compliant to real time constraints. In most cases real-time means that there's always a deterministic time in which something happens. Deterministic time being ussually a very low time value in the microseconds/milliseconds range.
Real time systems depend solely on this criteria, as the specificiations usually say something like 'Every x (period of time) (do something | check something)'. Usually this happens if the system interfaces with external sensors and controls life-saving or life-threatening systems.
I was working on an in-car navigation and infotainment system developed mostly in C/C++ with an operating system configured specifically to meet the real-time constraints to provide real-time navigation and media playback.
But this is not all to real-time systems: Usually the selection of algorithms in the entire system is made to have deterministic runtimes according to the Big-O notation, mostly using linear or constant time. Everything else is considered non-deterministic and thus not useable for real-time systems.
All of the real-time systems I have worked with were predominantly written in C with some bits of assembler, or written mostly in assembler with little bits of C. (Depending on whether we're talking the 90s and beyond, or the 80s, respectively.) However, some of the real-time systems I've worked with have used -- not exactly DSLs -- special homegrown code generators.
Real-time oriented language?
What is real-time
First we have to define what real-time mean.
Of course depending on how your tool will work against the physical environment pure real-time couldn't be effectively done, mostly because there will be a lot of third party dependencies.
If you are building embed stuff by using microcontrollers like arduino, the language to use will be limited by the hardware, but with more complex stuff like Raspberry Pi, the language choice is very wide.
Granularity
This is depending on what you are measuring, if you're working with:
weather temperatures, one read each 10 minute could be enough
people height or weight, one or maybe four read by day
server status, between 1 second for fine debugging to approx 1 hour for quiet unimportant secondary server.
atomic collision count: something finer...
Event based reading
The right (better) way for collecting data is based on value change event... whenever the device do permit it.
Your tool have to not poll values from device, but the device have to send values to your tool, when they change.
This could be done by using an hardware interrupt trigger or by using port protocole like RS-232 staying listening on some serial port, for sample.
Monitoring environment
The last thing to be warned is how legitimate user will interact with.
If you're building embed standalone device, like robot, you may use graphic libraries to interact with touch screen.
If you're building web based monitor, you may have to keep in mind that the client could be an old 800x600 monochrome screen, using poor internet connection and small processor... But depending on final goal if you may interact with clients, you could ensure strong hardware and strong internet connections. Anyway you have to watch for connexion loosing and event for communication delay between server and client. There is mostly third party dependencies.
Which programming language?
From there, the language choice is wide and clearly depend on
your knowledge.
granularity requested (by using event-based too, of course)
the amount of time you have to build the tool (money;)
delay, co-workers...
kind of device
kind of monitoring
some other political reasons
You could build real-time monitoring engine by using bash and sql only, I've seen sophisticated engines that was built under postgresql only... I've personally built a web based, solar energy monitor by using perl, mysql and javascript.
I cannot believe no one has mentioned LabVIEW programming language which is widely used for Real-time safety-critical systems. It has extensive libraries and well-known design patterns for architecturing and implementing for RT systems.
Also National Instruments makes various hardware (cRIO, PXI and etc) which are designed for real-time applications.
We use LabVIEW for Fracking (Hydraulic Fracturing) which is used in safety-critical environments.
PLCs run ladder and fbd code which is really a real-time dsl in the sense that your options are so limited that it is difficult to program in a way that would result in unpredictable runtime performance
A really purposeful application of the C language to real-time programming - and all related issues (such as parallel programming) - is offered by my Kickstarter
http://www.kickstarter.com/projects/767046121/crawl-space-computing-with-connel
It is called "Wide Programming" and I've been doing it most of my life. The rewards include a software library and a book - designed to be useful.
the company I've been working for since 2003 has been developing and deploying a Scada/Mes platform. Original implementation started in 1993, used Modula2 on OS/2. Later (1998) it was ported to Ada95 and Windows. Currently (2019) we use Ada compiler by AdaCore. Our system was ported and has been deployed to 32/64 Windows, HPUX, OpenVMS (and lately even to Raspberry). We have multiple installation in central Europe (gas industry, refineries, factories, power plants).
We feel Ada's features give our system a high degree of reliability and prevents a lot of errors that would easily occour if we used languages like C.
See also my blog
https://www.ipesoft.com/en/blog/what-language-is-the-d2000-written