The CNC system is a special real-time multi-task computer system, and its control software incorporates many advanced technologies in today's computer software technology, the most prominent of which are multi-task parallel processing and multiple real-time interrupts. They are introduced separately below.

1. Multi-task parallel processing

(1) Multitasking of CNC system. CNC system is usually used in industrial automation production as an independent process control unit, so its system software must complete two tasks of management and control. The management part of the system includes input, I/O processing, display and diagnostics. The control part of the system includes decoding, tool compensation, speed processing, interpolation and position control. In many cases, some aspects of management and control must be performed simultaneously. For example, when the CNC system is working in the processing control state, in order for the operator to know the working state of the CNC system in time, the display module in the management software must run simultaneously with the control software. When the CNC system works in the NC processing mode, the part program input module in the management software must run simultaneously with the control software. When the control software runs, some of its own processing modules must also run at the same time. For example, in order to ensure the continuity of the machining process, that is, the tool does not stop cutting between blocks, the decoding, tool compensation and speed processing modules must run at the same time as the interpolation module, and the interpolation must be carried out at the same time as the position control.

The task decomposition diagram of the CNC system (Figure 3-10(a)) and the task parallel processing relationship diagram (Figure 3-10(b)) are given below. In Figure 3-10(b), the two-way arrows indicate that there is a parallel processing relationship between the two modules.

(2) The concept of parallel processing. Parallel processing means that the computer completes two or more tasks of the same or different nature at the same time or within the same time interval. The most significant advantage of parallel processing is to increase the speed of operation. Comparing the n-bit serial operation with the n-bit parallel operation, under the condition of the same processing speed of the components, the operation speed of the latter is almost n times higher than that of the former. This is a parallel processing method with repeated resources, which greatly improves the operation speed according to the principle of "winning by quantity". But parallelism goes beyond simple duplication of devices, it has more implications. Such as time overlap and resource sharing. The so-called time overlap is that according to the pipeline processing technology, multiple processing processes are staggered in time, and several parts of the same set of equipment are used in turn. On the other hand, resource sharing is based on the principle of "time sharing", so that multiple users can use the same set of equipment in chronological order.

In the hardware design of CNC system, the parallel processing method of resource repetition has been widely used, such as the use of multi-CPU system architecture to improve the speed of the system. In the software design of the CNC system, the pipeline processing technology of time-sharing and resource overlapping is mainly used.

(3) Time-sharing of resources. In a single-CPU CNC system, the principle of CPU time-sharing is mainly used to solve the simultaneous operation of multiple tasks. Generally speaking, in a computer system using time-sharing and parallel processing, the first problem to be solved is the allocation principle of CPU time occupied by each task, which has two meanings: one is when each task occupies the CPU; the other is The second is the length of time each task is allowed to occupy the CPU.