HP Vectra Technical Reference Manual page 112

4.3.3.1 V_S8259 Driver (BP
=
001 EH)
The V_S8259 driver services the HP 8259A slave interrupt controller. Three interrupt request
lines are connected to this controller; the 8041 SVC (Service port) service request, the HP-HIL
controller, and the 8041 OBF (Output Buffer Full) service request.
When this driver is initialized, the interrupt vectors for the three interrupts listed above are set for
their respective entry points into the V_S8259 driver. When an interrupt occurs, control is
transferred to one of the three entry points. The V_S8259 driver will perform an F _ISR call to
one of three drivers; the V_8041 driver for the 8041 SVC interrupt, the V_HPHIL driver for the
HP-HIL controller interrupt, and the INT 09H driver for the 8041 OBF interrupt.
In the case of the 8041 SVC interrupt and the HP-HIL controller interrupt the corresponding
interrupt is masked off on the HP slave controller and an End-of-Interrupt command is sent to the
master interrupt controller before passing the interrupt on (via F_ISR). This allows other
interrupts even of lower priority to be serviced on the HP slave 8259A but does not require
interrupt handlers to be interrupt reentrant since the same interrupt is not allowed to fire until
the entire driver chain has completed processing. When these two driver chains finish processing
the V_S8259 issues a specific End-of-Interrupt command to the HP 8259A slave controller and
then unmasks the corresponding interrupt so it can fire again.
In the case of the 8041 OBF interrupt a specific End-of-Interrupt is sent to the HP slave controller
before passing on the interrupt, allowing the industry standard INT 09H driver to manage the
master 8259A controller as if the HP slave controller were not present.
In addition to initiating response to the hardware interrupts, the 8259A driver contains other
functions which initialize the interrupt vectors, and program the proper parameters into the HP
8259A slave interrupt controller.
V_S8259 Driver Function Definitions
A summary of the V_S8259 function codes is provided in table 4.13.
Input System and HP-HIL 103