Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ukma!husc6!ogccse!afoster
From: afoster@ogccse.ogc.edu (Allan Foster)
Newsgroups: comp.sys.mac.programmer
Subject: Re: If Apple implements user mode, how will we do uninterrupted I/O?
Keywords: user mode interrupt
Message-ID: <4111@ogccse.ogc.edu>
Date: 6 Aug 89 22:35:50 GMT
References: <8538@batcomputer.tn.cornell.edu>
Reply-To: afoster@ogccse.UUCP (Allan Foster)
Organization: Oregon Graduate Center, Beaverton, OR
Lines: 42

In article <8538@batcomputer.tn.cornell.edu> eacj@tcgould.tn.cornell.edu (Julian Vrieslander) writes:
>Tech Note #85 says that we should not disable interrupts from within an
>application.  There is an ominous admonition that "there will come a time
>[...]
>What does Apple really mean when they say that the interrupt mask may
>become inaccessible in some future System version, or on some future Mac?
>My reading of the Motorola manuals indicates that applications running in
>user mode will not be able to directly modify the interrupt mask in the
>status register of a 680xx CPU.  If applications must run in user mode,
>will Apple provide a trap (or another mechanism) that will allow an
>application to disable interrupts?
>
>If not, what is the recommended way of doing uninterrupted I/O?  I believe
>that 

It seems to me that the driver that you are writing really should
be an OS level task.  I am sure there would be a way under the new systems
to install a driver that would run in supervisor mode.  That would solve half 
your problem.  I however as another application on this machine would be
very upset if I were not serviced for severasl seconds.....

It seems the real solution to the problem is to do it in hardware... 
Get a board that can do DMA or has some sort of buffering on board
so that it does not require the attention of the host CPU as much.

Maybe putting a 68000 on the board with some ram would solve the problem
quite nicely.

If Mac is ever going to run as a protected memory virtual machine,
then running in USER mode is a MUST.  You do not own any hardware
as a user process, only access to a virtual machine!

Regards
Allan Foster
MicroPhone II Development Team



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