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From: hamilton@uiucuxc.CSO.UIUC.EDU
Newsgroups: net.micro.amiga
Subject: Re: ASDG recoverable ramdisk (review of
Message-ID: <148600142@uiucuxc>
Date: Thu, 18-Sep-86 15:24:00 EDT
Article-I.D.: uiucuxc.148600142
Posted: Thu Sep 18 15:24:00 1986
Date-Received: Sat, 20-Sep-86 23:51:27 EDT
References: <167@picuxa.UUCP>
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Nf-From: uiucuxc.CSO.UIUC.EDU!hamilton    Sep 18 14:24:00 1986


>Wait a second...it DOESN'T use AllocMem()? Then it CANT be compatible.
	compatible with what?  it sounds like it uses Allocate()
(which is what AllocMem() uses).

>Consider what happens if an interrupt routine wants to write to a file,
>and writes out to this ram disk. THERE IS NO GUARANTEE THAT AllocMem()'s
>DATA WILL BE CONSISTENT. The Ram disk looks at inconsistent data, grabs
>memory that may be returned by AllocMem, presto!
	hey, that's not unique to ASDG's ramdisk driver.  the AmigaDos
ram-handler would be just as susceptible.

>This obviously means that the Ram: disk cannot work during interrupts,
>but it has no way to tell if its caller was working from an interrupt
>routine or not. And there is no problem with writting to disk files
>during an interrupt routine.
	have you actually tried doing disk i/o in an interrupt routine?!
i wouldn't...  even if it were "safe", other interrupts could get fouled
up while you're waiting for such a slow process to complete.  you're
concerned that the memory list may be in an unstable state when the
interrupt occurrs; suppose the disk device's message list is likewise
unstable at the time you send an i/o request?
	if i wanted to do i/o from an interrupt, i'd use a second, "soft"
interrupt routine, and have the hardware interrupt Cause() the soft one.
the soft interrupt would live in normal tasking space.

	wayne hamilton
	U of Il and US Army Corps of Engineers CERL
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