Hard Real-Time with Windows XP
Blue Screen - so what?
The point at which Windows XP enters a Blue Screen, CeWin immediately intercepts the exception and makes a context switch to Windows CE in the processor: the Windows XP blue screen handler is frozen and CeWin triggers an event to which the application programmer is able to react. The programmer can now decide, for example, that the machine should continue to be operated normally, because it will not, in any case, be necessary to look at the display in the near future or during the current production shift. The machine can therefore continue its production process through to the end of the shift in the normal way. At the end of the shift, the machine is then restarted.
The programmer can also decide to bring the machine into a safe state before initiating a full restart. The decision as to what should be done after a Blue Screen is determined by the real-time side.
KUKA Controls has produced a special uploader (a type of boot loader) using a driver which is started with Windows. When the machine is restarted, the booting sequences are precisely controlled to ensure that CeWin is rebooted to a consistent state.
Full Scalability
CeWin is an open system rather than an independent real-time operating system. It is a combination of two standard solutions - Windows XP and Windows CE. From the latest version of CeWin (V3.3) onwards, CeWin supports all processors, both single and dual core, and nearly all PC platforms.
In addition, Windows CE is an independent operating system, meaning it also functions as a standalone solution. This makes it possible to scale products, so that a low-end version can run solely under Windows CE while the same application, in the high-end version, is integrated with Windows XP via CeWin offering far more options. As a result, Phoenix Contact is in a position to react very flexibly to the needs of its customers, and to adapt its product range to the market in each case, or even, if appropriate, to individual requirements.
Debugging Made Easy
Another problem with real-time driver extensions is the issue of how debugging should function. Under CeWin, developers are able to operate the real-time environment in the same way as a standalone control computer and connect to Windows CE remotely or through the CeWin shared memory network. The entire range of Windows CE development and source code tools is available for this purpose, and debugging is also easy to run.
In contrast, if a non-CeWin conventional real-time extension is used at the driver level, proprietary development systems must be installed on the system, since remote debugging is not possible. This was also a significant factor for the developers at Phoenix Contact when they decided to use CeWin.
Why CeWin?
Phoenix Contact conducted intensive research into real-time extensions for Windows XP, and explored the feasibility of developing its own extension, but determined the cost would be high. In addition, the developed, proprietary extension would also have to be maintained by them further adding the cost. It elected instead to focus on its core business, control solutions. After a number of different solutions for this real-time requirement had been considered from different viewpoints, with intensive investigation of the commercial aspects as well as the technical qualities, CeWin emerged as the optimum solution. Thanks to the ease of developing the company was quickly able to put its plans into action.
Furthering the quick adaptation to the Windows CE operating system was the relatively ease of connection to the existing XP system via a virtual network. Each operating system (both Windows CE and Windows XP) regards the other system on the PC as being simply a network subscriber, and can therefore use it as a base for all network services.
Windows XP and Windows CE can share the use of the network drives, perform FTP tasks and meet all the requirements which are based on the TCP/IP stack. This made it relatively simple to connect Windows CE to the Windows XP hard drive via a network drive using mounting. This does, however, have the disadvantage that if Windows XP crashes, the hard disk can no longer be accessed since the hard drive is controlled by Windows XP. However, Phoenix Contact has configured its solution in such a way that the real-time environment can continue to operate fully if a Blue Screen occurs in Windows XP.
Real-time Ethernet is also a Possibility
PC WORX systems communicate with the outside world via plug-in cards or Ethernet. The system supplier ensures that the plug-in cards are assigned to the real-time system, and that Windows XP is unable to access them. This is necessary because interrupts are not shared between Windows XP and Windows CE, which guarantees that no other interrupt can put a brake on the real-time system. However, the use of interrupts can be shared within the real-time system - and this is a real advantage of CeWin.
Phoenix Contact uses its own network card for the real-time application, so that the computer has two network connections: one for Windows XP and one for Windows CE. This is necessary, because the control systems also process real-time Ethernet protocols, which need to continue running under all circumstances, even during a Windows XP Blue Screen of Death (BSOD) event.
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