DE29620374U1 - Interrupt system for implementing a real-time capable control program in a non-real-time capable operating program - Google Patents

Description

Beckhoff Ind. Electronics**-* 6fefe-35802*

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Description

The invention relates to an interrupt system for implementing a real-time capable control program in a non-real-time capable operating program.

Personal computers (PCs) are increasingly being used to control machines and production plants. The main advantage of PC-based control systems compared to conventional programmable logic control solutions (PLC/CNC) is the ability to use generally applicable computer standards that are specified by international standards and through widespread successful use on the market. This results in a cost-effective control solution on the one hand, and at the same time ensures the use of the latest technology thanks to the short innovation cycles in PC development.

As a first approach to using PCs in automation systems, special PC modules were integrated into existing PLC/CNC control systems. However, the use of additional external PCs, especially for visualizing and logging the control process, makes such control systems complex and expensive.

The integration of PLC/CNC functions into the PCs themselves has therefore emerged as a much more promising solution for using PCs for control tasks. The extremely rapid and continuous increase in the performance of PC processors in recent years has made it possible to simultaneously handle control tasks in real-time operation, i.e. processing information at the same time and at the same speed as it is generated, and classic PC functions using a single processor. This solution approach is not only cost-effective,

score advantages, but also offers greater flexibility in adapting the control to desired applications.

In order to be able to carry out real-time control using a PC, it must provide sufficient computing power for all tasks that arise and thus enable stable process control. More precisely, the PC must ensure cyclic processing of a control task without temporal fluctuations, i.e. with a jitter in the range of a few microseconds, with a predictable latency time, i.e. the response time of the control to a control request.

Ideally, no additional operating system needs to be implemented on the PC for real-time tasks, but the operating system implemented to perform the usual PC functions also provides real-time control. However, almost all operating systems known to date do not meet the real-time requirements mentioned above. This applies in particular to the standard operating systems for PCs from Microsoft.

In particular, Windows operating systems are only very inadequately suited to time-critical control tasks, since interrupt requests that occur under these operating systems do not have direct access to the PC processor. If a control task is to be carried out by the PC processor under Windows operating systems, a virtual machine manager takes over the allocation of processor resources after the interrupt call. However, this intermediate virtualization increases the latency significantly, especially if the execution of the earlier interrupt request has to be interrupted when higher priority interrupts arrive. Furthermore, the constancy of the latency, which is essential for control tasks, is not guaranteed under Windows operating systems, because the operating systems react at different speeds depending on the type of interrupt call. However, since Windows operating systems are the platforms for PCs with the

largest application software offering, it would be particularly desirable to be able to perform real-time tasks under these operating systems.

To solve the problem of non-real-time capable operating systems, DE 44 06 094 A1 proposes to ensure the real-time execution of a control program by carrying out a complete environment change from the non-real-time capable operating system to the real-time capable control program by directly accessing the non-maskable interrupt (NMI) of the processor. However, this environment change via the non-maskable interrupt requires additional hardware for the PC system with which the calls for the non-masked interrupt can be generated. Furthermore, the method proposed in DE 44 06 094 A1 has no knowledge of the current state of the operating system when accessing via the non-maskable interrupt, so that it is also stopped at critical code sections that must be processed without interruption, which can lead to instability in the operating system. This applies in particular when using the method according to DE 44 06 094 Al, with the Windows NT operating system, which is particularly suitable for supporting complex automation tasks. In this operating system, the non-maskable interrupt is intended for "fatal" hardware errors in the processor. When the non-maskable interrupt is called, Windows NT therefore ensures a HALT state with a system message. Since the operating system kernel of Windows NT always expects this HALT state when the non-maskable interrupt is called, its use for carrying out environment changes for real-time operation of control tasks is prohibited. Finally, in the method known from DE 44 06 094 Al, only the jump into the operating system is defined using a non-maskable interrupt. However, no defined end of the control program executed in real time is provided, so that the operating system is not allowed to

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There may not be enough time to execute the control program the next time it is called.

The object of the invention is therefore to create an interrupt system for implementing a real-time capable control program in a non-real-time capable operating program, which enables real-time applications under the non-real-time capable operating program without endangering the stability of the operating program.

This object is achieved by a system according to claim 1. Preferred embodiments are specified in the dependent claims.

The interrupt system according to the invention is based on a deterministic time distribution between the real-time capable control program and the non-real-time capable operating program, i.e. the real-time capable control program carries out its tasks on the PC's processor at times that are accepted by the non-real-time capable operating system.

In order to achieve such deterministic behavior, according to the invention, two interrupts are triggered per operating cycle of the PC system, with one interrupt carrying out an environment change from the non-real-time capable operating system to the real-time capable control program and the other interrupt carrying out an environment change from the real-time capable control program to the non-real-time capable operating program, so that in one operating cycle, runtimes are assigned to both the real-time capable control program and the non-real-time capable operating program. The necessary interrupt requests for triggering the interrupt routines are carried out by an internal or external interrupt source of the PC system, whereby according to an advantageous embodiment, the timers of the PC system that cause the system clock calls, i.e., for example, timer 0, can be used for this purpose.

Furthermore, in the interrupt system according to the invention, the operating cycle of the PC system is programmed by the interrupt

The interrupt sequence of the interrupt source can be freely set, whereby a cycle time of 0.1 msec to 1 msec is preferably selected in order to ensure stable program execution of the real-time capable control program and the non-real-time capable operating program.

Furthermore, in the interrupt system according to the invention, the ratio between the runtime of the real-time control program and the runtime of the non-real-time operating program can also be changed, whereby a minimum runtime can be assigned to the non-real-time operating program. This makes it possible to achieve an optimal distribution of the computing capacity of the PC processor both to the control tasks and to the normal PC functions, whereby the stability of the non-real-time operating system is ensured by ensuring a minimum runtime. Furthermore, this runtime ratio can also be continuously modified during the processing of the real-time control program in order to be able to carry out necessary adjustments to the real-time operation, e.g. in the event of an increased "real-time load".

The solution approach according to the invention enables a stable implementation of a real-time capable control program in a non-real-time capable operating program on a processor, whereby it is particularly ensured that time-critical operating system tasks, such as network, hard disk or COM port tasks, are processed safely without interruption. Furthermore, no extensive additional hardware is required for the PC system to carry out the control tasks, since the PC resources managed by the non-real-time capable operating system can be used at the same time for the real-time operation of the control program.

In order to be able to carry out secure real-time operation, according to a preferred embodiment, security measures are provided against unwanted reprogramming of the interrupt source. After setting up the operating cycle on the PC system, this prevents the time interval from being changed.

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the interrupt calls of the interrupt source are effectively prevented until the real-time capable control program has been completed or its external interruption.

Under the Windows NT operating system, there is also the problem that the system timer service routine is often restarted shortly after it is regularly restarted in order to better distribute the system loads that occur. According to the invention, such a restart is identified and an undesirable call to the real-time control program triggered by the restart is prevented.

The invention enables non-real-time capable operating systems to be equipped with real-time properties in an open and compatible manner and thus to make them available to a PC that can efficiently handle "hard real-time" for all areas of automation without a complex and additional operating system and coprocessor cards. This applies in particular to the standard operating systems from Microsoft and in particular to the Windows NT operating system, which is explained in more detail below as an example using the attached drawings.
In the drawings show

Figure 1 shows part of an interrupt system according to the invention with a timer system and an interrupt controller system in a block diagram; and

Figure 2 shows another part of the interrupt system according to the invention.

As shown in Figure 1, the interrupt system contains a timer system 1 with a timer 0 (OUTO), which in the present embodiment also serves as a system timer. The interrupt calls issued by this timer 0 via an interrupt line IRQO are fed to an interrupt controller system (2, 3) that usually consists of two interrupt controllers and that triggers an interrupt in the processor of the PC system via a processor line INTR.

As shown in Figure 2, the interrupt system uses the interrupt number contained in the interrupt signal as an index

in an interrupt vector table 4 and reads the corresponding descriptor, which contains a selector and an offset. The selector serves as an access key to a code segment descriptor in a global or local descriptor table 5. This enables the processor to find out the code segment in a memory 6 that contains the interrupt routine for the triggered interrupt. The offset serves as an entry point into this code segment and represents the start address of the interrupt routine. When an interrupt is called by timer 0, the system clock routine is usually triggered under the Windows NT operating system.

According to the invention, in a first step the timer 0 is set to the desired operating cycle, preferably in the range of 0.1 msec to 1 msec via the multimedia timer.

Resolution with the same calls for Windows NT functions. Timer 0 generates predictable interrupt calls, which are stored under the interrupt vector INT30H in the interrupt vector table 4. This interrupt vector is overwritten according to the invention so that it indicates the address of the implementation routine written in the memory 6. Furthermore, calls from the Windows NT operating system to reprogram timer 0 are suppressed until the real-time capable control program is run through or interrupted.

After reprogramming, timer 0, which determines the operating cycle of the PC system, issues two interrupt calls per operating cycle. The time intervals between these two interrupt calls can be freely set, so that any time ratio between the sequence of interrupt calls in an operating cycle can be set. The implementation routine always triggers an environment change from the Windows NT operating system to the real-time control program at the first interrupt call and an environment change from the real-time control program to the Windows NT operating program at the second interrupt call. For the environment change from the

The system clock routine is used to integrate the control program into the Windows NT operating program. During the execution of the control program, the time ratio between the two interrupt calls of timer 0 can be continuously changed, although a minimum runtime is guaranteed for the Windows NT operating system in order not to endanger its stability during time-critical functions.

In the Windows NT operating system, there is also the problem in connection with real-time operation that the operating system after a regular call to the service routine of timer 0 often calls it again a short time later in order to achieve a better system load distribution. With the interrupt system according to the invention, these new calls are identified by the Windows NT operating system and unwanted triggering of the real-time control program is prevented.

After the control program has been processed or when it is interrupted, the original interrupt vector INT30H is written back into the interrupt vector table 4 so that the system clock routine of the Windows NT operating system is again pointed to for timer O interrupts. Furthermore, the blockage of reprogramming of timer 0 is removed, allowing the Windows NT operating system to restore its original behavior before the implementation of the real-time control program.

The interrupt system according to the invention thus enables a deterministic time distribution between the real-time control program and the Windows NT operating program, which is carried out synchronously with the system clock. The interrupt system according to the invention makes it possible to implement all types of control programs under the Windows NT operating program without changing the properties of this program.

However, the interrupt system according to the invention can not only be used with the Windows NT operating program, but is also suitable for all other non-real-time capable operating programs.

Claims (7)

Beckhoff Industrial Electronics - DEG-35802 Protection claims 1. Interrupt system for implementing a real-time capable control program in a non-real-time capable operating program on a processor of a PC system with an interrupt source (1) and an interrupt device (4, 5/6) connected to the interrupt source (1) for carrying out an environment change from the non-real-time capable operating program to the real-time capable control program in an operating cycle of the PC system analogous to a first interrupt call of the interrupt source, so that the real-time capable control program is assigned a fixed runtime in the operating cycle, characterized in that the interrupt source (1) is designed to trigger two interrupt calls in the operating cycle, and the interrupt device (4, 5, 6) is designed to carry out an environment change in the operating cycle of the PC system from the real-time capable control program to the non-real-time capable operating program analogous to the second interrupt call of the internal interrupt source, so that the non-real-time capable operating system is assigned a fixed runtime in the operating cycle. 2. System according to claim 1, characterized in that the interrupt source (1) is a timer of the PC system, which determines the system clock by means of the interrupt calls. • ft· «V ·· «&EEgr; 3. System according to claim 2, characterized in that the timer is programmable and a device is provided for setting the time intervals between the interrupt calls of the timer. 4. System according to claim 2 or 3, characterized in that the operating cycle is set by setting the interrupt call sequence of the timer, preferably between 0.1 msec and 1 msec. 5. System according to one of claims 2 to 4, characterized in that the timer is set with two alternating time intervals for triggering successive interrupt calls which determine the relationship between the running time of the real-time capable control program and the running time of the non-real-time capable operating program. 6. System according to one of claims 2 to 5, characterized by a device for identifying a triggering of the service routine of the timer by the non-real-time capable operating system and preventing the triggering of the real-time capable control program due to this triggering. 7. System according to one of claims 1 to 6, characterized by a device which, after setting up the operating cycle on the PC system with an environment change from the non-real-time capable operating program to the real-time capable control program and an environment change from the real-time capable control program to the non-real-time capable operating program, prevent the interrupt calls of the associated interrupt source from being changed until the real-time capable control program has been processed or is interrupted.