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From: gantose AT lerc DOT nasa DOT gov (Dave Gantose)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Please define "locking"
Date: Mon, 21 Aug 95 18:32:21 GMT
Organization: ADF, Inc.--NASA Lewis, Cleveland, OH
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Nntp-Posting-Host: babar.lerc.nasa.gov
To: djgpp AT sun DOT soe DOT clarkson DOT edu
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Thank you to Charles Sandmann who wrote:

>(...)
>So, you don't want anything you will touch in a hardware interrupt routine
>to every get paged out to disk (including the code,data,stack).  If you have
>enough memory on your machine that you never page (or have disabled virtual
>memory) this is not a problem.  If you do page, the DPMI page locking 
>services are a way to tell the paging mechanism to never take those pages
>out of memory, and avoid the problem.

I should have mentioned that I am programming for an embedded processor that 
will not have access to a hard drive, so I guess that if my programs don't die 
of memory exhaustion, then they are OK. However, the machines I develop and 
test upon DO have hard drives, so how would I disable virtual memory on them 
so that I don't have to deal with this?

>(...)
>Since it's very difficult to track down every memory address you might touch 
>in C, this is why you start worrying about GAS code so you have control over
>the location of the code and data so you know exactly what to lock.  The
>simple fix is to buy more memory (for everyone :-) so paging is eliminated.

And thanks to Mat Hostetter who wrote:

>I've written DPMI interrupt handlers that properly lock memory.
>Here's a quick, imprecise oversimplification of the issues involved
>(...)
>V2 is rock solid if you play by the rules.  Unfortunately, those rules are 
>tricky.

Even though I do not want to deal with this for my current application, I 
would still like to know how to do it right. Do either of you (or anyone else 
reading this) have a favorite example you could point me to? (I already have 
downloaded--but not yet studied--the Soundblaster library by Joel Hunter.)


=============================================================================
Dave Gantose
ADF, Inc.
2001 Aerospace Pkwy.           phone: (216)977-1376
Brook Park, OH  44142          email: Gantose AT lerc DOT nasa DOT gov