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> Sender: Reply-To: dixon@zephyrus.UUCP (Walter V. Dixon) Followup-To: 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)