Specifications

Device Driver Entry Points

Interrupt Service Routine

Processes interrupts generated by a device.

Speciﬁed in

UNIBUS, Q22–bus, and generic VAXBI devices require an interrupt service

routine for each interrupt vector the device has. Use the DPT_STORE macro to

place the address of the interrupt service routine into CRB$L_INTD+VEC$L_ISR.

If the device has two interrupt vectors, use the DPT_STORE macro to place the

address of the second interrupt service routine into CRB$L_INTD2+VEC$L_ISR.

Tape devices on the MASSBUS require an interrupt service routine that

interrogates the tape formatter (the controller) to determine which drive needs

attention and whether the interrupt is unsolicited.

Disk devices on the MASSBUS use the interrupt service routine provided by the

operating system and do not need to provide their own interrupt service routine.

Called by

The interrupt service routine is called either by the system interrupt dispatcher

(for direct-vectored adapters) or by an adapter interrupt service routine (for

non-direct-vector adapters).

Synchronization

A driver’s interrupt service routine is called, executes, and returns at device IPL.

In a multiprocessing environment, the interrupt service routine must obtain the

device lock associated with its device IPL. It performs this acquisition as soon as

it obtains the address of the UCB of the interrupting device. It must release this

device lock before dismissing the interrupt.

Context

At the execution of a driver’s interrupt service routine, the processor is running

in kernel mode on the interrupt stack. As a result, an interrupt service routine

can reference only those virtual addresses that reside in system (S0) space.

If an interrupt service routine uses R6 through R11, the AP, or the FP, it must

ﬁrst save the contents of those registers, restoring their contents before exiting by

means of the REI instruction. MASSBUS drivers must also preserve the contents

of R0 and R1.

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