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From: everett@hpcvlx.HP.COM (Everett Kaser)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Have Loadable Drivers Been Extended Since DOS 2.11?
Message-ID: <101000057@hpcvlx.HP.COM>
Date: 20 Jul 89 15:03:02 GMT
References: <112@isgtecXE12JC\>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 38


 bmw@isgtecXE12JC\ (Bruce Walker) writes...
>I have been writing an MSDO+ character-type loadable driver based on
>the old MSDOS 2.11 manual section on 9]@riting Device Drivers".  This
>driver properly requires an "open" and "close" call, which MSDO+ 2.11
>drivers don't support.

>Just from curiosity, I dissassembled a driver that I had kicking
>around, and I discovered that the driver header bit-word had an
>"undocumented" bit set (bit 11'SR  I then discovered that the "command
>decoder" part of the driver jumped on command numbers \G'] and 14.
>Ay 2.11 docs only list valid commands from 0 through 12.

>Could this "new bit" mean "Extended Post-DOS 2.11 Driver"?

>Could these extra commands be "open" and "close"?

>Bruce Walker                   ...uunet!mnetor!lsuc!isgtec!mutant!bmw

An excellent source for the answers to these and MANY other questions about
device drivers is the book "Writing MS-DOS Device Drivers" by Robert S. Lai,
The Waite Group, published by Addison-Wesley, ISBN 0-201-13185-4, $24.95 (US).

Starting on page 338 is a full description of the attribute word and it's use
by both character and block device drivers.  For character drivers, bit 11
means: 0=OPEN/CLOSE not supported, 1= OPEN/CLOSE supported (DOS 3.0 and above).
For block drivers, 0=REMOVABLE MEDIA not supported, 1=REMOVABLE MEDIA
supported.  Also added at 3.0 was a definition for bit 13 for character devices
which is 1=Output Til Busy command available for character devices.  At 3.2,
they added a couple of more commands for block devices (with some spares in
between) and command numbers can now be from 0 to 24.  And yes, commands 13
and 14 are DEV_OPEN and DEV_CLOSE, respectively.

If you're writing a device driver, get the book, it's worth the investment.

Everett Kaser                   "Your thoughts create your reality."
!hplabs!hp-pcd!everett
everett%hpcvlx@hplabs.hp.com