This may be a foolish question but I've been searching around for some time and don't see a clear answer. I've seen several microcontrollers advertised as running Unix-like software (Linux, Ubuntu) for example, the BeagleBone Black and Arduino Yun. Can someone please explain to me the benefit of this? So far I've used a couple of microcontrollers like the Arduino Uno/Duo, Freescale FRDM and STM32 Discovery which either didn't have this feature or I was not aware of it. I'm starting to see it more and more on newer microcontrollers so I'd like to know what it brings to the table.
Full disclosure: I've had minimal exposure to UNIX and its variants so far so please talk slowly and use small words =)
Hope to hear from you,
Yusif Nurizade
You get complex drivers already included Linux for free (USB, internet protocols, storage media and file systems).
You can use lots of free software for the things not included in the kernel.
It is simpler to develop software on a full OS (easier to debug, look what is going on, change the configuration, etc etc).
The drawback is that the real-time capabilities are generally worse than for some small RTOS, and it needs more resources (a couple of megabytes memory).
In the heart of all Android and iphone is a Embedded Linux System. Without getting too deep
Linux + Java = Android
BSD Unix variant + C/C++/Object C = iOS
Now if you get deeper the above two statement can be argued for accuracy
All Android devices run on ARM based microprocessors. Beaglebone is one such open source hardware platform with can run Android as well as Embedded Linux distribution and even a Ubuntu.
Now (IMHO) Ubuntu is primarily for desktop and server application. Many of the popular computer server farms uses Ubuntu.
Now STM32 is a ARM based CORTEX-M micro control. Once again (IMHO) is mostly used for bare metal embedded applications. I have hard that FreeRTOS can be ported to TM4C123 ARM Cortex-M TM4C123.
Now the advantages of using Linux base micro controller architecture are
OS is free for the most part
Larger community of users
The industry is moving towards open source
Lot of free resources get up to speed
Disadvantage are
Learning curve is pretty steep
Expect to stumble and fall a few time
Below to two good resources to learn Beaglebone open source development
Beaglebone
Introduction to Beaglebone development by Derek Molloy of Dublin City University
HTH and good luck
I'm moving from windows programming (By windows programming I mean using Windows API) to Linux Programming.
For programming Windows, the option we have is Win32API (MFC is just a C++ wrapper for the same).
I want to know if there is something like Linux API (equivalent to WINAPI) that is exposed directly to the programmer? Where can I find the reference?
With my little knowledge of POSIX library I see that it wraps around part of Linux API. But what about creating GUI applications? POSIX doesn't offer that. I know there are tons of 3rd party Widget toolkits like gtk, Qt etc. But I don't want to use the libraries that encapsulates Linux API. I want to learn using the "Core Linux API".
If there are somethings that I should know, please inform. Any programmer who is familiar with both Windows & Linux programming, please map the terminologies of Linux world so that I can quickly move on.
Any resources (books,tutorials,references) are highly appreciated.
I think you're looking for something that doesn't exactly exist. Unlike the Win32 API, there is no "Linux API" for doing GUI applications. The closest you can get is the X protocol itself, which is a pretty low level way of doing GUI (it's much more detailed and archaic than Win32 GDI, for example). This is why there exist wrappers such as GTK and Qt that hide the details of the X protocol.
The X protocol is available to C programs using XLib.
What you must understand is that Linux is very bare as to what is contained within it. The "Core" Linux API is POSIX and glibc. Linux is NOT graphical by default, so there is no core graphics library. Really, Windows could be stripped down to not have graphics also and thus not have parts of the win32 API like GDI. This you must understand. Linux is very lightweight compared to Windows.
For Linux there are two main graphical toolkits, GTK and Qt. I myself prefer GTK, but I'd research both. Also note that GTK and Qt exist for Windows to, because they are just wrappers. If you go take a look at the X protocol code for say xterm, you'll see why no one tries to actually creating graphical applications on top of it.
Oh, also SDL is pretty nice, it is pretty bare, but it is nice if your just needing a framebuffer for a window. It is portable between Linux and Windows and very easy to learn. But it will only stretch so far..
Linux and win aren't quite as different as it looks.
On both systems there exists a kernel that is not graphical.
It's just that Microsoft doesn't document this kernel and publishes an API that references various different components.
On Unix, it's more transparent. There really is a (non-GUI) kernel API and it is published. Then, there are services that run on top of this, optionally, and their interfaces are published without an attempt to merge them into an imaginary layer that doesn't really exist.
So, the lowest GUI level is a the X Window System and it has a lowest level library called Xlib. There are various libraries that run on top of this one, as you have noted.
I would highly recommended looking at the QT/C++ UI framework, it's arguably the most comprehensive UI toolkit for any platform.
We're using it at work developing cross platform apps that run on windows, osx and linux.
It also runs on Nokia's smart phone Operating System Maemo which has recently been merged with Intel's Moblin Linux OS, now called MeeGo.
This is going to sound insane since you're asking about "serious" stuff like C++ and C (and the "core linux API"), but you might want to consider building in something else. For instance:
Java Swing (many people love it! Others hate it and call it obsolete)
Mono GTK# (C# or VisualBasic or whatever you want, lots of people say it's pretty cool, but they're not not that many people)
Adobe AIR (ActionScript, you might hate it)
Titanium (totally new and unproven, but getting a lot of buzz in the iPhone world, at least)
And many other possibilities, some of which let you work on multiple platforms at once.
Sorry if this answer is not at all what you're looking for. The "real" answers on Linux are "pick a toolkit," which is also no answer at all :)
Have a look at Cairo. This something roughly similar to GDI+ and is under the hood of some of of the few usable GUI programs for Linux i.e. Firefox or Eclipse (SWT). It wraps most the natsy and ancient Linux stuff for you into a nice API that runs on most Linux installations without locking you into a entire subsystems like GTK or QT.
There is also the docs for the two different desktop platforms: Gnome and KDE that might help you down that road.
I'm getting started developing with OpenGL ES on ARM/Linux, and I would like to draw something full-screen but don't know where to start.
I'm not developping on iPhone, nor Android. This is a Linux/OpenGL ES question.
I know it's possible to draw on the framebuffer with OpenGL ES without any library but I don't find any resources about that topic, could you help me?
I don't have any code to show how to do it but basicly you use de framebuffer device as the target of OpenGL|ES operations.
Are you developing with an embedded platform as a target? If so, you could use software implementations on your host system and then the actual driver on the embedded device.
There is a small project for supporting OpenGLES 1.1 on linux called dlges. You could also try mesa.
I imagine that the driver itself might have a header for OpenGL that you could look at and see if it supports OpenGLES calls. Alternatively, you could set up function pointers to make your OpenGL Code look more like OpenGL ES.
Good luck!
Don't forget that desktop Linux comes with OpenGL, not OpenGLES! They're similar but not quite compatible. If you want to do work on OpenGLES on a desktop Linux platform, ARM or otherwise, you'll need an OpenGLES emulator library. Sorry, can't recommend any, I'm looking for one myself.
OpenGLES just handles the process of drawing stuff into the window. You also need a windowing library, which handles the process of creating a window to draw stuff into, and an event library, which deals with input events coming back from the window.
SDL will provide both of the last two, as will a bunch of other libraries. Khronos themselves have standardised on EGL as the windowing library and OpenKODE as the event library... but I don't actually know where to get open source implementations of these for Linux. (I work for a company that does EGL and OpenKODE for embedded platforms, so I've never needed to find an open source version!)
ARM offers few GPUs that support OpenGL 2.0. You can find some examples and and emulator that runs on linux on the Mali Developer site.
Of course that's mostly to target ARM GPUs, but I am pretty sure it could be used to examine OpenGL ES programming possibilities.
Here is a tutorial showing how to use SDL in combination with OpenGL ES. It's for the OpenPandora platform, but since that runs Linux, it should be applicable on the desktop if you can get the proper library versions.
Use of SDL is more or less standard with this kind of programming, in Linux. You can of course go the longer route and open the window yourself, attach a GL rendering context and so on, but usually it's easier to learn the relevant parts of SDL. That also gives you easy-to-use API:s for input reading, which is almost always necessary.
You can use PowerVR SDK for Linux http://community.imgtec.com/developers/powervr/graphics-sdk/
There are a lot of samples.
In windows, what does Flash use under the hood?
It's a relatively simple question which I can never find the answer to. Is it GDI (for windows VM implementations) or something else?
You don't need to go into any of the new GPU acceleration features of Flash. I just really want to know the inner workings because it's NEVER discussed.
On 64-bit Linux, the Flash plugin does not link against SDL (according to ldd). It does, however, link against GTK, GDK, and Cairo. It appears, therefore, that it is using either Cairo or raw Xlib calls to do its drawing on Linux.
I don't know on Windows. Flash tends to have minimal dependencies, but Direct-X may be standard enough that they use it. With some kind of a process examiner to tell you what libraries a process has loaded, you could examine a simple web browser embedding Flash and see what system facilities are actually in use.
DirectX mostly. It's hard to achieve good graphics performance with GDI.
I agree with george, GDI is very bad for speed. DirectX for Windows and SDL or similar for Linux (note this is an assumption!). In that sense it probably uses a layer that communicates with the native graphics subsystem on whatever platform it's running on.
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Now I'm sure we're all well aware of the relative merits of Linux vs Windows Desktop. However I've heard much less about the world of embedded development. I'm mainly interested in solutions for industry and am therefore uninterested about the IPhone or Android and more interested in these two OSes.
What are the relative trade-offs between the two platforms in the embedded world? If you were considering building a box for a specific project with custom hardware, a partially customised OS and a custom app then which would you choose and why?
I would assume that Windows CE wins on tools and Linux wins on both cost and possibly performance. However this is just utter speculation. Does anyone have any facts or experience of the two?
I worked for several years at a company that provided both CE and Linux for all of their hardware, so I'm fairly familiar with both sides of this equation.
Tools: Windows CE tools certainly are better than those provided by Linux, though the linux tools are certainly getting better.
Performance: Windows CE is real-time. Linux is not. The linux kernel is not designed for determinism at all. There are extensions that you can add to get sort-of real time, but CE beats it.
Cost: This is an area of great misunderstanding. My general experience is that CE is lower cost out of the box ($1k for Platform Builder and as low as $3 per device for a shipping runtime. "What?" you ask? "Linux is free." Well, not really so much, especially in the embedded arena. Yes, there are free distributions like Debian. But there are plenty of pieces that you might need that aren't in that free category. UI frameworks like QT, Java runtimes and media codecs just as a start. Also, most Linux distributions with a commercially-backed support system (e.g. MontaVista) are far from free.
Source Availability: Linux proponents may like to say that CE is a bad choice due to lack of source code. All I can say is that in over a decade of working with CE, half of which spent doing custom kernel and driver work for custom boards, I've only ever had need for source that didn't ship with CE (they ship a vast majority of it) once. I like having source too, but Microsoft provides support, so in the rare case you might think you need that source, you can get them to fix the problem (the one time we needed source, Microsoft provided a fix, and for free - which is their model under CE.
Does this mean that CE wins every time? No. I wouldn't suggest that at all. If you are a Linux shop and you have lots of Linux experience and code assets, you'd be foolish to run out and go CE. However, if you're coming into it from scratch CE usually has a lower TCO. Developers with Win32/C# experience are more prevalent and consequently less expensive. You also get a lot more "in the box" with CE than most other distributions, meaning faster time to market if you don't already have these things done in-house already.
I'll speak for the Linux side, at least for the category of software I'm familiar with (which is RF data collection equipment). Or industrial apps vs. consumer apps.
Windows CE (and its associated tools) IMH fairly recent E) is strongly biased to creating a "Windows Experience" on a small screen. The user input mode emphasizes mouse-like actions. Logons, application selection, etc. all try to be as similar to standard Windows as possible.
If a user is driving a lift truck, or filling a picking cart, or moving material from one place to another, there's a problem.
And it's a moving target - particularly on the .NET side. The Compact .NET runtime is seriously handicapped, and important libraries (like networking, data handling, and UI) are incomplete and versions too often deprecate the previous version. . CE seems to be the stepchild in the Windows family (possibly because there's not a lot of active competition selling to the hardware integrators.)
A nice stable rows-and-columns Linux console is a pretty handy context for many (in my experience most) high-use apps on a dinky screen.
Not much good for games on your cell-phone or Zune, though.
NOTE:
I think ctacke probably speaks accurately for the hardware integrator's side. I'm more aligned with the players further down the pipe - software integrators and users.
Choice is often made largely on perception and culture, rather than concrete data. And, making a choice based on concrete data is difficult when you consider the complexity of a modern OS, all the issues associated with porting it to custom hardware, and unknown future requirements. Even from an application perspective, things change over the life of a project. Requirements come and go. You find yourself doing things you never thought you would, especially if they are possible. The ubiquitous USB and network ports open a lot of possibilities -- for example adding Cell modem support or printer support. Flash based storage makes in-field software updates the standard mode of operation. And in the end, each solution has its strengths and weaknesses -- there is no magic bullet that is the best in all cases.
When considering Embedded Linux development, I often use the iceberg analogy; what you see going into a project is the part above the water. These are the pieces your application interacts with, drivers you need to customize, the part you understand. The other 90% is under water, and herein lies a great deal of variability. Quality issues with drivers or not being able to find a driver for something you may want to support in the future can easily swamp known parts of the project. There are very few people who have a lot of experience with both WinCE and Linux solutions, hence the tendency to go with what is comfortable (or what managers are comfortable with), or what we have experience with. Below are thoughts on a number of aspects to consider:
SYSTEM SOFTWARE DEVELOPMENT
Questions in this realm include CPU support, driver quality, in field software updates, filesystem support, driver availability, etc. One of the changes that has happened in the past two years, is CPU vendors are now porting Linux to their new chips as the first OS. Before, the OS porting was typically done by Linux software companies such as MontaVista, or community efforts. As a result, the Linux kernel now supports most mainstream embedded cpus with few additional patches. This is radically different than the situation 5 years ago. Because many people are using the same source code, issues get fixed, and often are contributed back to the mainstream source. With WinCE, the BSP/driver support tends to be more of a reference implementation, and then OEM/users take it, fix any issues, and that is where the fixes tend to stay.
From a system perspective, it is very important to consider flexibility for future needs. Just because it is not a requirement now does not mean it will not be a requirement in the future. Obtaining driver support for a peripheral may be nearly impossible, or be too large an effort to make it practical.
Most people give very little thought to the build system, or never look much beyond the thought that "if there is a nice gui wrapped around the tool, it must be easy". OpenEmbedded is very popular way to build embedded Linux products, and has recently been endorsed as the technology base of MontaVista's Linux 6 product, and is generally considered "hard to use" by new users. While WinCE build tools look simpler on the surface (the 10% above water), you still have the problem of what happens when I need to customize something, implement complex features such as software updates, etc. To build a production system with production grade features, you still need someone on your team who understands the OS and can work at the detail level of both the operating system, and the build system. With either WinCE or Embedded Linux, this generally means companies either need to have experienced developers in house, or hire experts to do portions of the system software development. System software development is not the same as application development, and is generally not something you want to take on with no experience unless you have a lot of time. It is quite common for companies to hire expert help for the first couple projects, and then do follow-on projects in-house. Another feature to consider is parallel build support. With quad core workstations becoming the standard, is it a big deal that a full build can be done in 1.2 hours versus 8? How flexible is the build system at pulling and building source code from various sources such as diverse revision control systems, etc.
Embedded processors are becoming increasingly complex. It is no longer good enough to just have the cpu running. If you consider the OMAP3 cpu family from TI, then you have to ask the following questions: are there libraries available for the 3D acceleration engine, and can I even get them without being committing to millions of units per year? Is there support for the DSP bridge? What is the cost of all this? On a recent project I was involved in, a basic WinCE BSP for the Atmel AT91SAM9260 cost $7000. In terms of developer time, this is not much, but you have to also consider the on-going costs of maintenance, upgrading to new versions of the operating system, etc.
APPLICATION DEVELOPMENT
Both Embedded Linux and WinCE support a range of application libraries and programming languages. C and C++ are well supported. Most business type applications are moving to C# in the WinCE world. Linux has Mono, which provides extensive support for .NET technologies and runs very well in embedded Linux systems. There are numerous Java development environments available for Embedded Linux. One area where you do run into differences is graphics libraries. Generally the Microsoft graphical APIs are not well supported on Linux, so if you have a large application team that are die-hard windows GUI programmers, then perhaps WinCE makes sense. However, there are many options for GUI toolkits that run on both Windows PCs and Embedded Linux devices. Some examples include GTK+, Qt, wxWidgets, etc. The Gimp is an example of a GTK+ application that runs on windows, plus there are many others. The are C# bindings to GTK+ and Qt. Another feature that seems to be coming on strong in the WinCE space is the Windows Communication Foundation (WCF). But again, there are projects to bring WCF to Mono, depending what portions you need. Embedded Linux support for scripting languages like Python is very good, and Python runs very well on 200MHz ARM processors.
There is often the perception that WinCE is realtime, and Linux is not. Linux realtime support is decent in the stock kernels with the PREEMPT option, and real-time support is excellent with the addition of a relatively small real-time patch. You can easily attain sub millisecond timing with Linux. This is something that has changed in the past couple years with the merging of real-time functionality into the stock kernel.
DEVELOPMENT FLOW
In a productive environment, most advanced embedded applications are developed and debugged on a PC, not the target hardware. Even in setups where remote debugging on a target system works well, debugging an application on workstation works better. So the fact that one solution has nice on-target debugging, where the other does not is not really relevant. For data centric systems, it is common to have simulation modes where the application can be tested without connection to real I/O. With both Linux and WinCE applications, application programing for an embedded device is similar to programming for a PC. Embedded Linux takes this a step further. Because embedded Linux technology is the same as desktop, and server Linux technology, almost everything developed for desktop/server (including system software) is available for embedded for free. This means very complete driver support (see USB cell modem and printer examples above), robust file system support, memory management, etc. The breadth of options for Linux is astounding, but some may consider this a negative point, and would prefer a more integrated solution like Windows CE where everything comes from one place. There is a loss of flexibility, but in some cases, the tradeoff might be worth it. For an example of the number of packages that can be build for Embedded Linux systems using Openembedded, see.
GUI TRENDS
It is important to consider trends for embedded devices with small displays being driven by Cell Phones (iPhone, Palm Pre, etc). Standard GUI widgets that are common in desktop systems (dialog boxes, check boxes, pull down lists, etc) do not cut it for modern embedded systems. So, it will be important to consider support for 3D effects, and widget libraries designed to be used by touch screen devices. The Clutter library is an example of this type of support.
REMOTE SUPPORT
Going back to the issue of debugging tools, most people stop at the scenario where the device is setting next to a workstation in the lab. But what about when you need to troubleshoot a device that is being beta-tested half-way around the world? That is where a command-line debugger like Gdb is an advantage, and not a disadvantage. And how do you connect to the device if you don't have support for cell modems in New Zealand, or an efficient connection mechanism like ssh for shell access and transferring files?
SUMMARY
Selecting any advanced technology is not a simple task, and is fairly difficult to do even with experience. So it is important to be asking the right questions, and looking at the decision from many angles. Hopefully this article can help in that.
I have worked in projects that involved customizing the software of an OEM board and I wouldn't say that Linux is cheaper. When buying a board you also need to buy the SDK. You still need to pay even for the Linux version. Some manufacturers offer both Windows CE and Linux solutions for their boards and there isn't a price difference. For Windows CE you also need the Platform Builder and pay for the licenses, but it is easier to go without support.
Another important issue is if you are building a User Interface or a headless device. For devices that require an LCD screen and human interaction is much easier to go with Windows CE. If on the other hand you are building a headless device, Linux may be a sounder option - especially if network protocols are involved. I believe that Linux implementations are more reliable and easier to tweak.
With Linux you are never on you own and you are never dependent on one single entity to provide permissions. There are many support options and you have the freedom to choose your support options for any part of the system through many competing sources.
With Windows CE you must adhere to the license and restrictions as set forth in the complex license agreements that must be agreed to. Get a lawyer. With windows CE you have only one proprietary source for OS support and you will proceed only as they see fit to support and provide what you need. You may not agree with their position, but will not have any recourse but to bend to what they prescribe. The costs of incremental components, modules, development kits, licensing, and support tend to pile up with proprietary platforms. In the longer term, what happens when the vendor no longer desires to support the platform and you do not have the rights to support and distribute it yourself? What happens when the vendor moves to newer technology and wants you to move along with them even though you may not be ready to make the move? $$$
Our experience with Windows solutions in general is that they tend to become more expensive over time. What was originally considered lowest TCO gravitates quickly towards and solution that is encumbered and costly to maintain and support. Licenses have to be re-negotiated over time and the new technologies, often unneeded, are forced into the picture at the whim of the provider for the sake of THEIR business needs. On top of that, the license agreements are CONTINUALLY changing--get a lawyer.
With Linux you have the freedom to provide in-house support and expertise without being encumbered against distributing the solution as you need. You also have the freedom to continue to use and support technology that original providers no longer want to support. Having the source code and the RIGHTs to do with it what you want (GPL, LGPL) is a powerful attractor when it comes to business continuity and containing costs while providing access to the very latest technologies or technologies that fit your needs.
I have developed network drivers that work both on RT Linux (to be more specific, Linux preemptive kernel with RT patch) and Windows CE. My experience was windows CE was more stable in terms of real-time response. Frame timings also showed that windows CE had less jitter.
On RT Linux, we had all sorts of problems. For example, when user moved the mouse; our frames were being delayed. Guess what, certain variants of x-windows disable interrupts. You may also feel that you are safer on console screen only. If you have VGA frame buffers enabled, you are doomed again. We had only one problem with windows CE in terms of jitter again. The problem happened when the USB controller was set to an incorrect mode in the BIOS and windows CE was using lots of time for polling.
To be honest, windows CE had more support. On Linux, you are on your own. You have to read every possible mailing list to understand what problems you may hve.
a partially customised OS
Is much easier to achieve if the OS is open source (and you have the expertise).
Android is a good option for some embedded systems.(it's linux based)
You have many experts that are able to develop on this system.
You have access to many libraries in java or C.
but it uses lot of memory and energy.
What we often forget with paid / licenced software is that you have to deal with licenses. It takes time and energy! Then you have to track if you pay it correctly. It involves many different people with different skills and it costs in decision.
This cost is often not included in the studies that show that open-source/free is more expensive than paid software.
With "free software" it's way easier to deal with licenses and you spend less time on dealing with these issues. Personally I prefer to avoid unnecessary communications with your legal / financing team every time you change some pieces of the software.