| Currently,most Virtual Instrument oriented VPLs (Visual programming Languages) are based on DHDF (Dynamic Homogeneous Dataflow) model. Because of it's natural data-driven property,DHDF can't work well with the event-driven operating systems that widely used. This leads to two demerits:one is inefficiency in use of CPU,the other is low respond-speed and poor real-time performance. Meanwhile,the developing of test & control technology also has given new demands on measurement software,that is,they hope the kernel software can efficiently use the hardware platform and carry currency into execution while still can rapidly reactive to and process external time-critical tasks.By the analysis of measurement & control systems and scheduling mechanism of related operating system,an ECDF (Event-Trigged Dataflow) model including a visual programming language called E was presented in this paper. Not only the formal description and the scheduling algorithm of ECDF model are depicted but also the E visual language and its development environment are depicted. Comparing with other VI (Virtual Instrument) oriented visual programming languages,the main contributions and innovations of E are:1. Multi-thread and concurrency. Some VICs (Virtual Instrument Controls) may have built in threads. So that operating models such as synchronous read,overlapped I/O and call back can be carried out in the thread.2. Event triggered. The "event triggered" has two meanings in E:one is the execution of thread control can be triggered by external event;the other is the HDFS (homogeneous dataflow scheduler) can be activated by other controls. Though HDFS is stilled used in E,it can automatic stop when there are no more controls in activated state.3. FIFO edges. A kind of edge with built in FIFO (first in first out) structure is introduced in E,this can resolve the connection and synchronization issuebetween thread controls to others. FIFO edge also can act as a data buffer when there is more data than the program can be processed. The more depth the FIFO has,the long time high-speed external data flow can E bearded with.4. Multi-viewer and main-sub program structure. The main diagram (or main program) and sub diagrams (or sub programs) are shown in different viewers of the frame widow and this can improve the intuition and readability of VPL.5. Six VIC models. According to the function and construct complicity,the controls in E can be separated in to six classes. A dual communication model within single resource has brought into practice use the thread VIC.6. Branch and loop structure. A kind of branch and loop structures has been proposed in E. It is easy to construct iteration and recursion with these structures.The test result has proved:Based on ECDF model,E has got a high executing efficiency and a well real-time performance over event-driven operating systems. It is not only suit for high speed burst data flow processing,but also can be used in reactive system design.In order to apply dataflow-based tools in real-time systems,a well-defined real-time semantics must be provided. Though RTL semantics can be used to describe Dataflow Language,some issues such as the depiction of the asynchronous node and the selection of time scale stilled have not been solved. In this paper,a RTL formal depiction of single-rate asynchronous dataflow language is presented. With bringing in the State Predicates and Transition Event Constants,the key problem of how to depict the asynchronous node can be resolved.
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