Huazhong CNC system software structure
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The software structure of the Central China CNC system is shown in Figure 1. The part below the dotted line in the figure is called the bottom software. It is the software platform of the Central China CNC system. The RTM module is a self-developed real-time multitask management module responsible for the task management management scheduling of the CNC system. The NCBIOS module is a basic input/output system that manages all external control objects of the CNC system, including device driver (I/O) management, position control, PLC control, interpolation calculation, and internal monitoring. The RTM and NCBIOS modules are collectively referred to as NCBASE, as shown by the double-dot wireframe in the figure. The portion above the dotted line in the figure is called process control software (or upper layer software), and it includes function submodules related to user operations such as editing program, parameter setting, decoding program, PLC management, MDI, and fault display. For different numerical control systems, the difference in their functions is at this level. The increase and decrease of system functions are performed at this level; each function module exchanges information with the bottom layer through NCBASE's NCBIOS. 
Fig.1 The software structure of Huazhong Numerical Control Device
(b) Functions of NCBASE
1. Real-time multi-task scheduling This function is implemented by the RTM module. The dispatch core consists of a clock interrupt service program and a task scheduler. as shown in picture 2. According to the scheduling mechanism required by the task (using priority preemption plus time-slice rotation scheduling) and the status of the task, the scheduling core performs management on the task, that is, which task is currently determined to obtain control of the CPU and monitor the status of the task. Each task in the system can only be run and terminated through the scheduling core. Figure 2 describes the relationship between the various tasks and the scheduling core. The solid line in the figure indicates the state from the scheduling core entering the task or the task failed to run within a time slice and returning to the scheduling core; the dotted line in the figure indicates that the task is in the time slice. After the operation is completed, the status of the dispatch core is returned. 
Figure 2 Multitasking schedule
2. Device driver
For different control objects, such as machining centers, CNC milling machines, CNC lathes, CNC grinders, etc., the hardware configuration may be different, and different hardware modules have different drivers. Huazhong Numerical Control System has solved this problem very well. When configuring the system, drivers for all hardware modules must be described in NCBIOS's NCBIOS.CFG (format: DEVICE=driver name). When the system is running, the NCBIOS calls the driver of the corresponding module according to the preset settings of NCBIOS.CFG and establishes the corresponding interface channel.
3. Position control
Position control is a fixed program of NCBIOS. It mainly accepts the position control commands sent from the interpolation operation program. After pitch error compensation, transmission gap compensation, and extreme position determination, the output speed command value is sent to the position control module.
4. Interpolator
Huazhong Numerical Control System is a multi-channel (four-channel) CNC system. Each channel has an interpolator, which creates an interpolation task accordingly. Its task is mainly to complete interpolation operations such as straight lines, arcs, threads, tapping and small straight line segments (for free curve and free-form surface processing).
5. PLC scheduling
The main tasks of PLC scheduling are: fault alarm processing; M, S, T processing; emergency stop and reset processing; virtual axis drive processing; tool life management; operation panel switch processing; indicator lights and emergency handling.
6. Internal monitoring
Realize the monitoring of faults in various parts of the CNC system.