The 10ms fixed interrupt is the most demanding part of the real-time system. It is the smallest time unit in the functional unit of the operating system. It mainly completes the detection and corresponding simple processing of real-time events. In this interrupt processing program, you need to complete the following tasks: scan the off-hook / on-hook status of all subscriber lines; detect whether there are user dial digits generated on the user line, including pulse dialing and dual tone dialing; check and set the timing Device; detects the status of the serial port.
The call processing process and system testing process often require access to various data or apply for related caches, various control blocks, and message buffer blocks during operation. The operating system provides this access capability to application processes through an interface called a primitive. The functions of primitives can be divided into the following categories: application, return, sending, delay and waiting of message blocks; query and modification of database; modification of scanning mode; sending of various digital signals; queue insertion, modification and deletion, and process Termination, etc. The primitive is implemented through software interruption. When the operating system is initialized, the starting address of the processing code of the primitive is written into the interrupt vector. If the application process needs to call the primitive function, the application process first pushes the primitive number and parameter table into the user stack, and then calls the software interrupt. If the called primitive number is within the normal range, jump to the corresponding according to the primitive number Primitive processing entry. After executing the corresponding function, the program restores various environment variables of the user process, opens the interrupt, and returns to the user process using the statement.
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