MVME297-256模擬量輸入模塊
?組中的項(xiàng)目可以是活動的或非活動的。?組可以是活動的或非活動的。對于每個活動組，DriveOPC中都有一個循環(huán)運(yùn)行的線程。線程從設(shè)備讀取活動項(xiàng)值，并在DriveWindow中調(diào)用所謂的通知接收器。DriveWindow內(nèi)的所有在線活動都使用此回調(diào)機(jī)制。?通常，當(dāng)從設(shè)備讀取或?qū)懭胫禃r，它也會緩存在DriveOPC中。?DriveWindow還可以直接讀取和寫入值，而無需回調(diào)。每個讀/寫操作可以包含多個項(xiàng)目。?DriveOPC緩存中值的初始質(zhì)量不好。DriveWindow不會自動從設(shè)備中讀取某些項(xiàng)目（如數(shù)據(jù)記錄器通道緩沖區(qū)），并且在用戶請求更新之前，它們的質(zhì)量一直很差。高級信息驅(qū)動窗口2 10-21如果使用本地服務(wù)器（EXE）版本，為了簡單起見，這里沒有顯示其他線程。需要它們，因?yàn)镈riveWindow和DriveOPC運(yùn)行的是獨(dú)立的進(jìn)程，因此具有獨(dú)立的地址空間。然而，操作系統(tǒng)負(fù)責(zé)線程同步。當(dāng)工作線程為客戶機(jī)線程執(zhí)行作業(yè)時，客戶機(jī)線程總是在等待，因此當(dāng)我們通過說客戶機(jī)線程完成作業(yè)來簡化時，我們不會失去任何重要的東西。一般的數(shù)據(jù)流結(jié)構(gòu)如下：當(dāng)一個線程（無論是內(nèi)部DriveOPC線程還是DriveWindow線程）訪問設(shè)備或DriveOPC內(nèi)的內(nèi)部數(shù)據(jù)結(jié)構(gòu)時，訪問由一個鎖同步，一次只允許一個線程處理數(shù)據(jù)。這意味著，例如，一個擁有大量活動項(xiàng)的組可以長時間阻止所有其他訪問，因?yàn)樗许?xiàng)都是在釋放鎖之前處理的。7.1.1屏幕刷新在這種情況下，用戶沒有直接請求更改屏幕上的值，但由于其他原因（例如，恢復(fù)最小化的DriveWindow），需要重新繪制屏幕。這些值從DriveWindow內(nèi)部緩存中提取。該操作在DriveWindow內(nèi)部完成。高級信息10-22 DriveWindow 2 7.1.2選擇更改在這種情況下，用戶更改瀏覽樹窗格中的選擇，并使用DriveOPC緩存的值重建項(xiàng)目集窗格。將數(shù)據(jù)記錄器顯示窗格中的選擇更改為已上載的數(shù)據(jù)記錄器的工作方式相同。該操作由DriveWindow線程使用非活動項(xiàng)完成。7.1.3更新在這種情況下，用戶請求DriveWindow更新所選項(xiàng)目或上載數(shù)據(jù)記錄器，數(shù)據(jù)將從設(shè)備中提取并緩存。
? 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.
