28 NetVista™ Technical Information Manual
following processing occurs to maintain compatibility with the IRQ2 used by IBM
computer products:
1. A device drives the interrupt request active on IRQ2 of the channel.
2. This interrupt request is mapped in hardware to IRQ9 input on the second
interrupt controller.
3. When the interrupt occurs, the system microprocessor passes control to IRQ9
(interrupt hex 71) interrupt handler.
4. This interrupt handler performs an EOI command to the second interrupt
controller and passes control to the IRQ2 (interrupt hex 0A) interrupt handler.
5. This IRQ2 interrupt handler, when handling the interrupt, causes the device to
reset the interrupt request before performing an EOI command to the master
interrupt controller that finishes servicing the IRQ2 request.
Hard disk drives and controller
Reading from and writing to the hard disk is initiated in the same way as in other IBM
computer products; however, new functions are supported.
Machine-sensitive programs
Programs can select machine-specific features, but they must first identify the
machine and model type. IBM has defined methods for uniquely determining the
specific machine type. The machine model byte can be found through Interrupt 15H,
Return Configuration Parameters function (AH)=(C0H).
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