Basic Interrupt Information for Programmers
An interrupt is a subroutine called asynchronously by external hardware (usually an I/O device) during the execution of another application. The CPU halts execution of its current process by saving the system state and next instruction, and then jumps to the interrupt service routine, executes it, loads the saved system state and saved next instruction, and continues execution. Interrupts are good for handling infrequent events such as keyboard activity. Interrupts on this cpuModule are controlled by two Intel
What happens when an interrupt occurs?
An IRQx pin on the PC/104 bus makes a low to high transition while the corresponding interrupt mask bit is unmasked and the PIC determines that the IRQ has priority, that is, the PIC interrupts the processor. The current code segment (CS), instruction pointer (IP), and flags are pushed onto the stack. The CPU then reads the
How long does it take to respond to an interrupt?
A DOS system can respond to an interrupt between 6 and 15 μs. A Windows system can take a much longer time when a service routine has been installed by a device driver implemented as a
Interrupt Request Lines
To allow different peripheral devices to generate interrupts on the same computer, the ISA bus has eight different interrupt request (IRQ) lines. On the ISA bus, a transition from low to high on one of these lines generates an interrupt request, which is handled by the PC’s interrupt controller. On the PCI bus, an interrupt request is
The interrupt controller checks to see if interrupts are to be acknowledged from that IRQ and, if another interrupt is already in progress, it decides if the new request should supersede the one in progress or if it has to wait until the one in progress is done. This prioritizing allows an interrupt to be interrupted if the second request has a higher priority. The priority level is based on the number of the IRQ; IRQ0 has the highest priority, IRQ1 is
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