Path: utzoo!attcan!uunet!steinmetz!zephyrus!dixon
From: dixon@zephyrus.steinmetz (Walter V. Dixon)
Newsgroups: comp.sys.ibm.pc
Subject: Re: help needed with device driver chai
Message-ID: <11306@steinmetz.ge.com>
Date: 21 Jun 88 15:01:41 GMT
References: <39500014@pyr1.cs.ucl.ac.uk> <5717@columbia.edu>
Sender: news@steinmetz.ge.com
Reply-To: dixon@zephyrus.UUCP (Walter V. Dixon)
Organization: General Electric CRD, Schenectady, NY
Lines: 42

Newsgroups: comp.sys.ibm.pc
Subject: Re: help needed with device driver chai
Summary: Locating device drivers
Expires: 
References: <39500014@pyr1.cs.ucl.ac.uk> <5717@columbia.edu>
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Reply-To: dixon@zephyrus.UUCP (Walter V. Dixon)
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Distribution:world
Organization: General Electric CRD, Schenectady, NY
Keywords: _MS DOS Papers_,Device Drivers, Driver Chain

Although there are two chapters which make reference to int 21h ah=52h,
the level of detail associated with this reply leads me to belive it
comes from one of the two chapters which I wrote.  Under DOS 3.0 and
above this method is indeed the correct way to locate a character device.
An alternative approach is to open the nul device with a FCB.  One
of the undocumented fields in the FCB is the address of the device
header.

Locating a block device is a bit more complicated.  Another field
in this list of list points to a structure known as the current directory
structure (CDS),  which in turn points to a linked list of device
control blocks (DCB).  The DCB contains the address of the device
header.

I have written a program which prints out extensive information about
the device driver chain (as well as info on cache and memory) usage.
I also have a "self-loading" ram disk driver which plugs into the
necessary DOS data structures and then does a terminate and stay
resident.

I have offered to make copies (sources included) of these programs.
Since some of the files on this disk appear in the manuscript,  it
is not clear that I can post them.  The agreement which I have with
the Waite Group lets me provide this disk for $10.00. (Lest someone
accuse me of commercialism,  this fee barely covers my costs).
Anyone who is interested can contact me by email.

I hope this helps.

Walt Dixon		(ARPA: Dixon@GE-CRD.ARPA)