MVME297-256模拟量输入模块
•组中的项目可以是活动的或非活动的。•组可以是活动的或非活动的。对于每个活动组，DriveOPC中都有一个循环运行的线程。线程从设备读取活动项值，并在DriveWindow中调用所谓的通知接收器。DriveWindow内的所有在线活动都使用此回调机制。•通常，当从设备读取或写入值时，它也会缓存在DriveOPC中。•DriveWindow还可以直接读取和写入值，而无需回调。每个读/写操作可以包含多个项目。•DriveOPC缓存中值的初始质量不好。DriveWindow不会自动从设备中读取某些项目（如数据记录器通道缓冲区），并且在用户请求更新之前，它们的质量一直很差。高级信息驱动窗口2 10-21如果使用本地服务器（EXE）版本，为了简单起见，这里没有显示其他线程。需要它们，因为DriveWindow和DriveOPC运行的是独立的进程，因此具有独立的地址空间。然而，操作系统负责线程同步。当工作线程为客户机线程执行作业时，客户机线程总是在等待，因此当我们通过说客户机线程完成作业来简化时，我们不会失去任何重要的东西。一般的数据流结构如下：当一个线程（无论是内部DriveOPC线程还是DriveWindow线程）访问设备或DriveOPC内的内部数据结构时，访问由一个锁同步，一次只允许一个线程处理数据。这意味着，例如，一个拥有大量活动项的组可以长时间阻止所有其他访问，因为所有项都是在释放锁之前处理的。7.1.1屏幕刷新在这种情况下，用户没有直接请求更改屏幕上的值，但由于其他原因（例如，恢复最小化的DriveWindow），需要重新绘制屏幕。这些值从DriveWindow内部缓存中提取。该操作在DriveWindow内部完成。高级信息10-22 DriveWindow 2 7.1.2选择更改在这种情况下，用户更改浏览树窗格中的选择，并使用DriveOPC缓存的值重建项目集窗格。将数据记录器显示窗格中的选择更改为已上载的数据记录器的工作方式相同。该操作由DriveWindow线程使用非活动项完成。7.1.3更新在这种情况下，用户请求DriveWindow更新所选项目或上载数据记录器，数据将从设备中提取并缓存。
• Items within a group can be active or inactive. • A group can be active or inactive. For each active group, there is a cyclically running thread within DriveOPC. The thread reads the active item values from a device and calls a so called advise sink within DriveWindow. This call-back mechanism is used by all on-line activities within DriveWindow. • Always, when a value is read from or written to a device, it is also cached within DriveOPC. • DriveWindow also reads and writes values directly without the call-back. Each read/write operation can contain several items. • The initial quality of values in the DriveOPC cache is bad. Some items (such as datalogger channel buffers) are not automatically read from a device by DriveWindow, and their quality stays bad, until the user requests updating of them. Advanced Information DriveWindow 2 10-21 In case the local server (EXE) version is used, there are additional threads not shown here for simplicity. They are needed because DriveWindow and DriveOPC are running is separate processes and thus have separate address spaces. The operating system, however, takes care of thread synchronisation. A client thread always waits while the working thread is executing a job for it, so we do not lose anything important when we simplify by saying that the client thread does the job. The general data flow structure is as follows: When a thread, whether an internal DriveOPC thread or a DriveWindow thread accesses a device or the internal data structures within DriveOPC, access is synchronised by a lock, which allows only one thread at a time to handle data. This means that a group having huge amount of active items, for example, can block all other access for a long time, because all the items are handled before the lock is released. 7.1.1 Screen Refresh In this case there no direct request from the user to change the values on the screen, but the screen needs to be redrawn for other reasons (restoring a minimized DriveWindow, for example). The values are drawn from the DriveWindow internal cache. The operation is done internally in DriveWindow. Advanced Information 10-22 DriveWindow 2 7.1.2 Selection Change In this case the user changes selection in the browse tree pane, and the item sets pane is reconstructed by using the values cached by DriveOPC. Changing selection in the datalogger display pane to an already uploaded datalogger works the same way. The operation is done by a DriveWindow thread using inactive items. 7.1.3 Update In this case the user requests DriveWindow to update the selected items or upload a datalogger, and the data is fetched from the device and cached.
