xref: /src/sys/arch/acorn32/doc/interrupts

/* $NetBSD: interrupts,v 1.1 2001/10/18 00:05:01 reinoud Exp $ */

/*
 * Copyright (c) 1996 Mark Brinicombe.
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Notes on interrupts.

Ok since interrupts can be chained the return value from an interrupt
handler is important.

The following return values are defined :

-1	- interrupt may have been for us but not sure so pass it on
0	- interrupt no serviced (not ours)
	  interrupt serviced but pass on down the chain
1	- interrupt serviced do not pass on down the chain

The important bit is whether the interrupt should be passed on down
the chain of attached interrupt handlers.

For some interrupts and drivers where only a single device is
ever expected, the interrupt should be claimed if it has been serviced.
Passing it on down the chain may result in the stray interrupt handler
being called.
There are however some interrupt that should *always* be passed on down
the chain. These are interrupt which may commonly have multiple drivers
attached.

The following interrupts should always be passed on (return value of 0)

IRQ_TIMER0
IRQ_TIMER1
IRQ_VSYNC
IRQ_FLYBACK
IRQ_PODULE

IRQ_CLOCK	(RC7500)

The following interrupts are recommended to be passed on

IRQ_DMACH0
IRQ_DMACH1
IRQ_DMACH2
IRQ_DMACH3
IRQ_DMASCH0
IRQ_DMASCH1

IRQ_SDMA	(RC7500)

All other interrupts are not expected to be shared and may be claimed
when serviced. Stray IRQ handlers may or may not be attached to the end
of these irq chains.