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From: Lewis_P@cc.curtin.edu.au (Peter Lewis)
Newsgroups: comp.sys.mac.programmer
Subject: Re: doing real work at interrupts
Message-ID: <4249.272ea016@cc.curtin.edu.au>
Date: 31 Oct 90 01:57:42 GMT
References: <1990Oct30.152816.2172@cs.umu.se> <2303@heavens-gate.lucid.com> <1990Oct30.131140.10113@hellgate.utah.edu>
Organization: Curtin University of Technology
Lines: 54

In article <1990Oct30.131140.10113@hellgate.utah.edu>,
     u-lchoqu%peruvian.utah.edu@cs.utah.edu (Lee Choquette) writes:
> In article <2303@heavens-gate.lucid.com> pab@lucid.com (Peter Benson) writes:
>>
>> It seems like what is needed is a general mechanism whereby any sort of
>> task can be initiated at interrupt level.  This would have to be done by
> 
> How about opening a "device driver" that doesn't actually do any
> reading or writing to a device, but has its "dNeedTime" flag set,
> indicating the system should call its control routine at specific
> intervals--or as often as possible if the drvrDelay word is zero.  The
> system doesn't actually call the control routine until the application
> calls SystemTask, but at that time you can go ahead and do all the
> memory movement you want.  I believe you can even do drawing and
> window management.
> 
> The main disadvantage to this scheme is that such drivers won't get
> called when the application is not calling SystemTask or WaitNextEvent,

   If you don't mind waiting until SystemTask is called, you could patch
SystemTask at the same time as you install your interupt handler.  Then
you could have the interupt handler set a variable (PC relative) to true
when the interupt occurs, and have your SystemTask patch test this and
do the interupt handling if it is true, and then call SystemTask.

   Pseudo Code -
NewSystemTask:        TEST    an_interupt_occured
                      JSR NE  Handle_Interupt
                      JMP     (original_SystemTask)

an_interupt_occured:  DC.W    0

InterupHandler:       SET     an_interupt_occured
                      RTS

(I assume SystemTask can move memory, I don't have IM handy.)

   I don't know if its any better/worse to install a patch or a device
driver, but its probably easier to install a patch. I really home Apple's 
Thought Police haven't been listening in to this discusion!

Happy Hacking,
   Peter.

PS: The UMPG looks really good!  Anyone who wants to post a question should
look there first (it answered my last posted question)
-- 
Disclaimer:Curtin & I have an agreement:Neither of us listen to either of us.
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