Interrupt Service Routines: Difference between revisions
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The [[:Category:x86|x86]] architecture is an interrupt driven system. External events trigger an interrupt - the normal control flow is interrupted and a ''' |
The [[:Category:x86|x86]] architecture is an interrupt driven system. External events trigger an interrupt - the normal control flow is interrupted and a '''Interrupt Service Routine''' (ISR) is called. |
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Such events can be triggered by hardware or software. An example of a hardware interrupt is the keyboard: Every time you press a key, the keyboard triggers IRQ1 (Interrupt Request 1), and the corresponding interrupt handler is called. Timers, and disk request completion are other possible sources of hardware interrupts. |
Such events can be triggered by hardware or software. An example of a hardware interrupt is the keyboard: Every time you press a key, the keyboard triggers IRQ1 (Interrupt Request 1), and the corresponding interrupt handler is called. Timers, and disk request completion are other possible sources of hardware interrupts. |
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Software driven interrupts are triggered by the int opcode; e.g. the services provided by MS-DOS are called by the software triggering INT 21h and passing the applicable parameters in CPU registers. |
Software driven interrupts are triggered by the int opcode; e.g. the services provided by MS-DOS are called by the software triggering INT 21h and passing the applicable parameters in CPU registers. |
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For the system to know which interrupt service routine to call when a certain interrupt occurs, offsets to the ISR's are stored in the |
For the system to know which interrupt service routine to call when a certain interrupt occurs, offsets to the ISR's are stored in the [[IDT|Interrupt Descriptor Table]] when you're in [[Protected mode]], or in the [[Interrupt Vector Table]] when you're in [[Real Mode]]. |
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An ISR is called directly by the CPU, and the protocol for calling an ISR differs from calling e.g. a C function. Most importantly, an ISR has to end with the iret opcode, whereas usual C functions end with ret or retf. The obvious but nevertheless wrong solution leads to one of the most "popular" tripple-fault errors among OS programmers. |
An ISR is called directly by the CPU, and the protocol for calling an ISR differs from calling e.g. a C function. Most importantly, an ISR has to end with the iret opcode, whereas usual C functions end with ret or retf. The obvious but nevertheless wrong solution leads to one of the most "popular" tripple-fault errors among OS programmers. |
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