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      1 /* $NetBSD: interrupts,v 1.1 2001/10/18 00:05:01 reinoud Exp $ */
      2 
      3 /*
      4  * Copyright (c) 1996 Mark Brinicombe.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  * 3. All advertising materials mentioning features or use of this software
     16  *    must display the following acknowledgement:
     17  *	This product includes software developed by Mark Brinicombe.
     18  * 4. The name of the company nor the name of the author may be used to
     19  *    endorse or promote products derived from this software without specific
     20  *    prior written permission.
     21  *
     22  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
     23  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     24  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     25  * IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
     26  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     27  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
     28  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     32  * SUCH DAMAGE.
     33  */
     34 
     35 Notes on interrupts.
     36 
     37 Ok since interrupts can be chained the return value from an interrupt
     38 handler is important.
     39 
     40 The following return values are defined :
     41 
     42 -1	- interrupt may have been for us but not sure so pass it on
     43 0	- interrupt no serviced (not ours)
     44 	  interrupt serviced but pass on down the chain
     45 1	- interrupt serviced do not pass on down the chain
     46 
     47 The important bit is whether the interrupt should be passed on down
     48 the chain of attached interrupt handlers.
     49 
     50 For some interrupts and drivers where only a single device is
     51 ever expected, the interrupt should be claimed if it has been serviced.
     52 Passing it on down the chain may result in the stray interrupt handler
     53 being called.
     54 There are however some interrupt that should *always* be passed on down
     55 the chain. These are interrupt which may commonly have multiple drivers
     56 attached.
     57 
     58 The following interrupts should always be passed on (return value of 0)
     59 
     60 IRQ_TIMER0
     61 IRQ_TIMER1
     62 IRQ_VSYNC
     63 IRQ_FLYBACK
     64 IRQ_PODULE
     65 
     66 IRQ_CLOCK	(RC7500)
     67 
     68 The following interrupts are recommended to be passed on
     69 
     70 IRQ_DMACH0
     71 IRQ_DMACH1
     72 IRQ_DMACH2
     73 IRQ_DMACH3
     74 IRQ_DMASCH0
     75 IRQ_DMASCH1
     76 
     77 IRQ_SDMA	(RC7500)
     78 
     79 All other interrupts are not expected to be shared and may be claimed
     80 when serviced. Stray IRQ handlers may or may not be attached to the end
     81 of these irq chains.
     82