Intel 210200-002 manual Interrupt, INT interrupt-type

INT	INTERRUPT	INT
Operation:	Flags Affected:
(SP) +- (SP) - 2	IF, TF
((SP) +1:(SP)) +- FLAGS
(IF) +- a
(TF) +- a
(SP) +- (SP) - 2
((SP) +1:(SP)) +- (CS)
(CS) +- (TYPE * 4 + 2)
(SP) +- (SP) - 2
((SP) +1:(SP)) +- (IP)
(IP) +- (TYPE * 4)
Description:
INT interrupt-type

INT (Interrupt) activates the interrupt pro- cedure specified by the interupt-type operand. INT decrements the stack pointer by two, pushes the flags onto the stack, and clears the trap (TF) and interrupt-enable (IF) flags to disable single-step and maskable interrupts. The flags are stored in the format used by the PUSHF instruction. SP is decremented again by two, and the CS register is pushed onto the stack. The address of the interrupt pointer is calculated by multiplying interrupt-type by four; the second word of the interrupt pointer replaces CS. SP again is decremented by two, and IP is pushed onto the stack and is replaced

by the first word of the interrupt pointer. If interrupt-type = 3, the assembler generates a short (1 byte) form of the instruction, known as the breakpoint interrupt.

Software interrupts can be used as "supervisor calls," i.e., requests for service from an operating system. A different interrupt-type can be used for each type of service that the operating system could supply for an applica- tion program. Software interrupts also may be used to check out interrupt service procedures written for hardware-initiated interrupts.

2-82