The identification mark of the interrupt source can be used to form the entry address of the corresponding interrupt service program or the first address of the interrupt service program is called the interrupt vector. The interrupt identification code generated by hardware in Pc/AT is called the interrupt type number (of course, the interrupt type number has other generation methods, such as directly given in the instruction, automatically formed by the CPU, etc.), that is, during the interrupt response 8259A What is generated is the interrupt type number of the highest priority interrupt source that is currently requesting an interrupt. There is the following relationship between the interrupt type number and the interrupt vector: Interrupt type number × 4 = the first address where the interrupt vector is stored With the first address where the interrupt vector is stored, what is taken out of the 4 storage units starting from this address is the interrupt service program Entrance.
Refers to the offset and segment base value of the entry address of the interrupt service program, and an interrupt vector occupies 4 bytes of space. The interrupt vector table is the lowest-end 1K byte space in the 8086 system memory. Its function is to store the corresponding interrupt vectors in the order of the interrupt type number from small to large. A total of 256 interrupt vectors are stored. During the interrupt response process, the CPU calculates the position of the corresponding interrupt vector in the table through the interrupt type number (interrupt vector number) obtained from the interface circuit, and obtains the interrupt vector from the interrupt vector table, turning the program flow to the entrance of the interrupt service program address.
The 80x86 system collects all interrupt vectors and stores them in a certain area of the memory in the order of the interrupt type number. The storage area for storing interrupt vectors is called the interrupt vector table, that is, the interrupt service program entry address table.
Since the interrupt vector table can be flexibly modified at the operating system level, the interrupt vector table of different systems may be different. In addition, Intel protects 32 interrupt numbers from 0x00 to 0x1F in the CPU protection mode. Under Linux, it is used for system interrupts from 0x20, including the interrupt reset of the 8259 chip.
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