From: Berlin@vireo.com
Subject: comp.os.ms-windows.programmer.drivers Frequently Asked Questions (FAQ)
Date: 30 Aug 1995 16:02:48 GMT
Organization: Vireo Software, Inc.
Expires: 28 Sep 1995 16:01:31 GMT
Summary: This posting contains Frequently Asked Questions (with answers) 
        for the comp.os.ms-windows.programmer.drivers newsgroup.
        This newsgroup addresses issues raised by people WRITING device
        drivers for Microsoft Windows.  Please do NOT post requests for
        device drivers in this group. Such requests should be directed to:
        comp.os.ms-windows.setup.

Archive-name: windows/programming/device-drivers
Posting-Frequency: bimonthly
Last-modified: August 10, 1995


                   Frequently Asked Questions (FAQ)
                                 for
                comp.os.ms-windows.programmer.drivers

Summary:
        This is a working document.  Suggestions, questions, answers,
        are welcome.  I will post this document near the beginning of
        each month.  This FAQ is particularly thin on Windows NT driver
        information (that's a hint for you NT driver wizards out there
        to send in some info...).

        Thanks for help, comments, and answers from Lee Fisher, Michael Geary, 
        Chris Marriott, Dan Norton, and especially Don Matthews.

        Edited by Steve Lewin-Berlin (Berlin@vireo.com)

Questions:

 1.  Help, I need a driver for...
 2.  What are the differences between device drivers for Win 3.1, Win 3.11,
     Win 95, and Win NT?
 3.  What is a VxD?
 4.  How do I access physical memory at <addr> from a Windows 3.1 application?
 5.  What are the differences between embedded, installable, and conventional
     device drivers?
 6.  I need to write a Windows device driver.  Should it be a DLL or a VxD?
 7.  How do I handle interrupts in my VxD?
 8.  How do I access physical memory in my VxD?
 9.  How do I access memory from my application or DLL in my VxD?
10.  Can I write device drivers in C/C++, or must I use assembly language?
11.  What commercial products are available to help write drivers?
12.  What books are available?
13.  What on-line resources are available?
14.  What other information is available?
15.  Other questions (full answers not written yet)
        What magazine articles have been published about driver development?
        How do I get a VxD ID from Microsoft, and why?
        What's the best place to get started on driver development?
        How do I call a Windows or DOS application from a driver?



Answers:

 1.  Help, I need a driver for ...

     I'm afraid you've asked on the wrong group. This is a newsgroup for
     discussions of device driver programming, not for requesting drivers for
     particular devices. I'm sure you'll get help if you ask on the correct
     newsgroup, which is "comp.os.ms-windows.setup".

 2.  What are the differences between device drivers for Windows 3.1,
     Windows 3.11, Windows 95, and Windows NT?

     Windows 3.x and Windows 95 share a common device driver model.  Windows NT
     depends an a completely new, and completely incompatible driver model.
     Let's discuss Windows 3.x and Windows 95 first, then a brief word about
     Windows NT, and finally some discussion about compatibility between NT and
     Windows 3.x/95.

     There are really two kinds of device drivers for Windows 3.x/95.  Virtual
     Device Drivers (VxDs) run as part of the privileged (ring-0) operating
     system. VxDs can be thought of as a DLL for the operating system.  Running
     at ring 0, VxDs have complete access to the physical hardware, and can
     access data in the address space of any DOS, Windows, or Protected Mode
     application.  Under Windows 3.x, VxDs are typically given a .386 file
     extension, and are loaded when Windows starts.  Under Windows 95, VxDs are
     given the .VXD file extension, and may be loaded at startup time, or
     dynamically loaded later.

     Windows 95 uses the same basic architecture for VxDs as Windows 3.x.
     Thus, drivers written for Windows 3.x can be loaded on a Windows 95 system
     and should generally work fine.  However, Windows 95 adds hundreds of new
     services for VxDs, and extends the VxD architecture to allow full dynamic
     loading, pageable code and data, access to the system registry,
interfaces to
     Win32 applications, and many other features.  VxDs written for Windows 95
     cannot be loaded on a Windows 3.x system.

     In addition to VxDs, Windows 3.x/95 supports non-privileged (ring-3)
     Communication and Printer drivers.  These are typically given .DRV file
     extensions. 

     Windows NT uses a new driver architecture, called "Kernel Mode Drivers".
     Refer to the Windows NT DDK for detailed information.  VxDs are not
     compatible with Windows NT.

     In order to provide compatibility between Windows NT and Windows 95/3.x,
     Microsoft provides "Miniport Drivers" for certain kinds of devices.
     Miniports allow driver developers to write a single driver using a
     pre-defined interface that is provided on both Windows NT and Windows
     95/3.x.  Microsoft provides Miniport drivers for SCSI, Printer, and
     Display devices. 

 3.  What is a VxD?

     "VxD" stands for Virtual "something" Device, where 'x' stands for
     "something". Microsoft often names drivers according to this convention,
     thus "VKD" is the Virtual Keyboard Device, and "VPICD" is the Virtual
     Programmable Interrupt Device.  VxDs are loaded into the protected
     (ring-0) operating system address space, and have full access to the
     system hardware.  VxDs can modify page tables directly, install true
     hardware interrupt handlers, and generally wreak unrestricted havoc on
     the system.

     VxDs can be used to virtualize physical hardware by intercepting
     application requests to use the hardware and arbitrating between
     requests from different applications. In the more extreme case, VxDs can
     provide a "virtual" device that is not actually present at all, by
     emulating the behavior of a hardware device.  VxDs, by virtue of their
     privileged access to the system, can also be used to implement software
     monitors, debuggers, and to modify the behavior of other software on the
     system.
     
 4.  How do I access physical memory at <e.g. D000:0000> from a
     Windows 3.1 application?

     This is very easy to do.  Here is a sample program that  references the
     VGA display buffer at A000:0000.  You can use the same technique, except
     use _D000h instead of _A000h.  KERNEL defines a whole set of these
     selectors for you covering the A000 through F000 range.

         #define STRICT
         #include <windows.h>

         typedef WORD SELECTOR;

         // __A000h is an absolute value; by declaring it as a NEAR variable
         // in our data segment we can take its "address" and get the
         // 16-bit absolute value.

         extern BYTE NEAR CDECL _A000h;

         SELECTOR selVGA = (SELECTOR)&_A000h;

         int PASCAL WinMain (HINSTANCE   hinst,
                             HINSTANCE   hinstPrev,
                             LPSTR       lpszCmdLine,
                             int         cmdShow
                             )
        {
        WORD FAR * lpVGA = MAKELP( selVGA, 0 );

        // Should put garbage pixels on top left of screen
        lpVGA[0] = 0x1234;
        lpVGA[1] = 0x5678;

        return 0;
        }


 5.  What are the differences between embedded, installable, and conventional
     device drivers?

     All of these terms can be used to describe 16-bit protected-mode DLLs.
     
   o An embedded device driver is a DLL that basically acts as an extension
     of a particular Windows application.  It usually contains an interrupt
     handler, and it exports any set of services the author might choose to
     implement.
 
   o An installable device driver must conform to more rigid guidelines.
     This type of driver can be opened, closed, enabled, disabled, etc. by
     other applications or DLLs.  It contains a DriverProc, which is like
     the WindowProc in a Windows application.  The DriverProc responds to
     a standard set of messages sent by Windows and to custom messages sent
     by applications.  This is the type of driver that can be installed
     using the Control Panel applet.
 
   o A conventional device driver (also sometimes called a "standard"
     device driver) interacts with a hardware device supported by the
     Windows API.  For example, the display, keyboard, and printer are
     considered to be "standard" devices.  These drivers are sometimes
     given a file extension of .DRV, and are usually installable drivers.
     They work with certain pre-defined data structures and provide certain
     pre-defined services.

 6.  I need to write a Windows device driver.  Should it be a DLL or a VxD?

     This is the kind of question whose answer really depends on your
     application and your objectives.  In general, a VxD is more difficult
     to develop, but yields higher performance when processing interrupts
     and accessing I/O ports.  A VxD can also do things that aren't
     otherwise possible with a DLL.
     
     The first step is to determine what it is that your driver must do.
     If it must support a hardware device, then which of the following
     system resources are required by your hardware?
 
     a.)  I/O ports
     b.)  IRQ lines
     c.)  Memory ranges
     d.)  DMA channels
 
     If I/O ports are involved, then be aware that there are performance
     issues related to accessing I/O ports from ring 3, as you would in a 
     DLL, as compared to accessing them from ring 0 in a VxD.  There is
     overhead associated with accessing I/O ports from ring 3, perhaps as
     much as 100% or more (i.e. ring 3 accesses take twice as much time as
     ring 0 accesses).
 
     If IRQ lines are involved, then be aware that there is significantly
     more interrupt latency associated with an ISR running in ring 3 than
     in a VxD.
 
     Access to physical memory can be accomplished with DPMI services in
     a DLL, or VMM services in a VxD.
 
     Access to DMA channels should go through VDS (Virtual DMA Services).
 
     If you need to make your hardware appear to be shared by Windows
     applications and DOS applications running in separate DOS boxes,
     then you need to "virtualize" your hardware with a VxD.  You also
     need to "virtualize" your hardware if you need to mediate access, or
     resolve contention for your device.

 7.  How do I handle interrupts in my VxD?

     You should use the services provided by the Virtual PIC Device (VPICD)
     to install an ISR for your hardware device.  This involves creating
     a data structure in the locked data segment of your VxD of type
     VPICD_IRQ_Descriptor.  In it, you specify the IRQ number and the
     address of your ISR, among other things.  You then register your
     ISR by calling VPICD_Virtualize_IRQ.  This returns an IRQ Handle,
     which you should save for future reference.
     
     Later, when an interrupt occurs, your ISR will be entered with minimal
     latency.  The ISR should be in a locked code segment.  The IRQ Handle
     that uniquely identifies this interrupt will be in EAX upon entry.
     You should call VPICD_Phys_EOI at the end of your ISR.  Just before
     returning from your ISR, clear the carry flag if you successfully
     processed the interrupt.  If the IRQ is sharable, you can pass the
     IRQ on to the next handler in the chain by setting the carry flag.
     Return from the ISR with a RET instruction, not IRET.
     
     Upon entry to the VID_Hw_Int_Proc (your ISR), interrupts are masked
     at the PIC for that particular interrupt, and an EOI has already been
     sent to the PIC for that same interrupt.  The call to VPICD_Phys_EOI
     at the end of the ISR doesn't actually send an EOI to the physical
     PIC, as the name implies, but rather simply unmasks the interrupt at
     the PIC. The EOI was actually sent to the PIC before entering
     VID_Hw_Int_Proc.  The name of the VPICD_Phys_EOI service is misleading.
 
     Check out the useful services provided by VPICD.

 8.  How do I access physical memory in my VxD?

     You should first convert the physical address to a linear address
     with the _MapPhysToLinear service.  Then convert the linear address
     to either a protected-mode address in <selector>:<offset> form or a
     V86-mode address in <segment>:<offset> form with the Map_Lin_To_VM_Addr
     service.

 9.  How do I access memory from my application or DLL in my VxD?

     You should convert the protected-mode address to a linear address
     with the Map_Flat service.  

10.  Can I write device drivers in C/C++, or must I use assembly language?

     VxDs are 32-bit programs.  You may use a 32-bit C/C++ compiler, but
     you must be careful about segmentation, calling conventions, and
     run time library routines that require initialization.  Many of the
     interfaces provided by the Virtual Machine Manager have register-based
     calling conventions.

     Vireo Software sells a toolkit that allows you to use C or C++ to
     write VxDs.  See below.

11.  What commercial products are available to help write device drivers?

        MSDN level 1   (Microsoft)
        MSDN level 2   (Microsoft)
        Soft-ICE/W     (Nu-Mega Technologies)
        VtoolsD        (Vireo Software)
        WinRT          (BlueWater Systems)

        MSDN level 1
            Summary:  Membership in level 1 of the Microsoft Developer Network
                      gets you a CD 4 times per year. The CD is packed with
                      documentation and on-line books, including articles about
                      VxD development.
            Contact:  Microsoft Developer Network
                      mail:  PO Box 10296, Des Moines, IA  50336
                      voice: (800) 759-5474
                      voice: (206) 936-8661
                      CIS:  go MSDS

        MSDN level 2
            Summary:  Membership in level 2 of the Microsoft Developer Network
                      gets you a set of CDs 4 times per year.  The CDs include
                      the level-1 CD (see above) plus operating systems, SDKs,
                      and DDKs for a number of MS products.  This includes the
                      Windows Device Driver Kit (DDK), which includes
                      utilities required to build device drivers, along with
                      numerous examples.
            Contact:  MSDN (see above)

        VtoolsD for Windows 3.1
            Summary:  VtoolsD is a toolkit that allows developers to build VxDs
                      in C or C++ using the Microsoft 32-bit C/C++ compiler.
                      VtoolsD includes a visual-programming VxD code generator,
                      ANSI C run-time libraries, VMM/VxD service libraries, 
                      and a VxD Class Library.  Compatible with Microsoft and
                      Borland C/C++ compilers.
            Contact:  Vireo Software
                      mail:  385 Long Hill Road, Bolton, MA  01740
                      voice: (508) 779-8352
                      fax:   (508) 779-8351
                      Email: Vireo@vireo.com

        VtoolsD for Windows 95 (Pre-release)
            Summary:  The Windows 95 Pre-release allows developers to build
                      VxDs that call new services available in Windows 95.
                      Requires Windows 95 DDK.
            Contact:  Vireo Software (see above)

        Soft-ICE/W
            Summary:  Soft-ICE/W is a full-screen character-mode debugger that
                      can be used to debug VxDs and applications. Soft-ICE/W
                      can debug VxDs at the instruction level, or display
                      ASM, C, or C++ source code.
            Contact:  Nu-Mega Technologies, Inc.
                      mail:  PO Box 7780, Nashua, NH  03060
                      voice: (603) 889-2386
                      fax:   (603) 889-1135
                      Email: info@numega.com
                      Compuserve: !GO NUMEGA

        WinRT
            Summary:  WinRT is a Win32 programmer's toolkit that allows a 
                      Win32 thread to perform Port I/O, Memory I/O and 
                      Interrupt without building a device driver.  Available
                      for Windows 95 and Windows NT.
            Price:
            Contact:  BlueWater Systems
                      mail:  PO Box 776, Edmonds, WA 98020
                      voice: (206) 771-3610
                      fax:   (206) 771-2742
                      Email: 73514.132@compuserve.com

12.  What books are available?

      Specifically about device drivers:

        Writing Windows Device Drivers           (Daniel Norton)
        Writing Windows Virtual Device Drivers   (Thielen and Woodruff)
        Writing Windows VxDs and Device Drivers  (Karen Hazzah)

      Useful to device driver developers:

        Undocumented DOS (2nd Edition)           (Andrew Schulman et al)
        DOS Internals                            (Geoff Chappell)
        Unauthorized Windows 95 Resource Kit     (Andrew Schulman)

      Reference:

            Title:      Writing Windows Virtual Device Drivers
            Author:     David Thielen and Bryan Woodruff
            Publisher:  Addison Wesley
            ISBN:       0-201-62706-X (may be replaced by:)
            ISBN:       0-201-48921-X
            Price:      $39.95

            Title:      Writing Windows Device Drivers
            Author:     Daniel Norton
            Publisher:  Addison Wesley
            ISBN:       0-201-57795-X
            Price:      $29.95

            Title:      Writing Windows VxDs and Device Drivers
            Author:     Karen Hazzah
            Publisher:  R&D Publications
            ISBN:       0-13-100181-7
            Price:      $49.95

            Title:      Undocumented DOS (2nd Edition)
            Author:     Andrew Schulman et al
            Publisher:  Addison-Wesley
            ISBN:       0-201-63287-X
            Price:      $44.95

            Title:      DOS Internals
            Author:     Geoff Chappell
            Publisher:  Addison-Wesley
            ISBN:       0-201-60835-9
            Price:      $39.95

            Title:      Unauthorized Windows 95 Resource Kit
            Author:     Andrew Schulman
            Publisher:  IDG Books
            ISBN:       1-56884-305-4 (with disk)
            ISBN:       1-56884-169-8 (no disk)
            Price:      ?


13.  What on-line resources are available?

            Internet news groups
                comp.os.ms-windows.programmer.drivers

            World Wide Web sites
                http://world.std.com/~vireo/
                http://www.albany.net/~danorton/ddk/

            DDK-L - Private Internet Mailing List ($15.00 fee)
                To join, send a message to "Majordomo@lori.albany.net"
                with the text "subscribe ddk-l email@host" in the body
                of the message.

            Internet FTP site
                ftp://ftp.microsoft.com/Developr/drg/developer-info/devinfo.zip
                        This file contains a list of developer resources
                        available from Microsoft; it is not driver specific.
                ftp://ftp.microsoft.com/Developr/MSDN/
                ftp://ftp.microsoft.com/Developr/DRG/MSDN-Info/
                        These directories contain additional information
                        about Microsoft Developer Network.

            CompuServe
                Microsoft operates several forums on CompuServe that may
                be of interest to device driver developers:

                Microsoft Windows SDK Forum     Service: WINSDK 

                    Developers using the Windows Software Development Kit [and
                    DDK] will want to take advantage of the community of
                    assistance and support available in the Windows SDK Forum.
                    Help is available for subjects such as tools, accelerators,
                    controls, dialogue boxes, memory management, fonts,
                    palettes and color [and device drivers].

                Microsoft Developer Knowledge Base      Service: MDKB  

                    The Microsoft Developer Knowledge Base is a reference tool
                    containing technical information and articles about the
                    Microsoft developer-specific products.  This database is
                    compiled and maintained by Microsoft Product Support and is
                    full-text, keyword searchable. You will find Microsoft
                    press releases and technical articles about product bugs,
                    trouble-shooting and updates.       

                Microsoft Developer Network Forum       Service: MSDNLIB

                    The Microsoft Developer Network (MSDN) Technical Library
                    Forum offers software developers a quick and efficient way
                    of obtaining technical information.  The libraries contain
                    a collection of technical articles in the Windows Help file
                    format and sample code, which are available for
                    downloading. Message sections enable you to discuss any of
                    the files or codes with other users, as well as with
                    Microsoft Representatives.

                Microsoft Knowledge Base        Service: MSKB

                    Microsoft Knowledge Base is a database which provides
                    access to information about Microsoft products previously
                    available only to the Microsoft support engineers. Search
                    the database by product name, version or category. Or for
                    immediate responses to your questions, perform a full-text
                    search of all documents contained within database that
                    contain the subject of your question. Also communicate
                    directly with Microsoft by sending an electronic message to
                    its Help Desk.

                Microsoft Service Request       Service: MSR

                    Microsoft offers the Service Request System as an optional,
                    private (fee-based per incident) technical support service
                    that offers to help solve complex development problems.
                    Other avenues, such as the Microsoft Developer Support
                    Forums and Microsoft Developer Knowlede Base, should be
                    consulted prior to using the Service Request System.

                Microsoft Software Library      Service: MSL

                    The Microsoft Software Library is a collection of uploaded
                    binary files, samples, technical notes and utilities about
                    various Microsoft programs.  The entire library is keyword
                    searchable and the files can easily be downloaded to your
                    computer.

14.  What other information is available?

        The October 1992 Microsoft Windows NT Device Driver Developer's 
        Conference video/audio tapes are still available. Contact:

              MobileTape Co. Inc.
              address: 25061 W. Stanford, Suite 70; Valencia, CA 91355, USA
              phone (orders): 800.369.5718
              phone (info): 805.295.0504
              fax: 805.295.8474

            ask for the order form for the event:

              Microsoft Windows NT Device Driver Developer's Conference
              October 26-28, 1992
              Anaheim, CA

        Solomon Software Technologies
        20 Hunters Lante
        Nashua, NH 03063-2245
        USA
        Phone: 1.800.492.4898
        Phone: 1.603.595.9059
        FAX: 1.603.595.9005
        Email: 71561.3603@CompuServe.COM

            They offer various technical seminars by folks such as Richard Hale
            Shaw, Jamie Hanrahan, Jeffrey Richter, and David Solomon. Topics
            include Visual C++, OLE, MFC, Windows '95 ("Chicago"), Win32
            programming, and Windows NT device drivers. One relevant seminar
            is "Windows NT Kernel-Mode Device Driver Programming".

15.  Suggested questions, full answers not written yet:

     What magazine articles have been published about driver development?
        <<Articles have been published in Windows/Dos Developer's Journal,
          Windows Technical Journal, Windows Sources, and others.  I haven't
          collected exact references.>>

     How do I get a VxD ID from Microsoft, and why?
        <<A VxD ID is required for drivers that export services to other
          drivers.  Alternative methods exist for drivers exporting services
          to DOS, Protected Mode, and/or Windows applications.  Send Email to
          VXDID@Microsoft.com for an application form.>>

     What's the best place to get started on driver development?
        <<one suggestion: Asche's "The Little Device Driver Writer" on
          the MSDN CD.  Another suggestion: get Vireo's VtoolsD for VxD
	  development>>

     How do I call a Windows or DOS application from a driver?
        <<See the VPOSTD example in the MS DDK, or the CLASSTUT example
          in Vireo's VtoolsD kit, for examples of how to call PostMessage>>


99.  Statement of interest

        The editor works for Vireo Software, Inc. and is one
        of the authors of the VtoolsD VxD toolkit mentioned
        in this document. 

        -- Steve Lewin-Berlin
           Berlin@vireo.com
           Vireo Software
           "The VxD Tools Company"


Stephen T. Lewin-Berlin
                                email: berlin@vireo.com
Vireo Software, Inc.            voice: (508) 779-8352
"The VxD Tools Company"         Fax:   (508) 779-8351
385 Long Hill Road              http:  //world.std.com/~vireo/
Bolton, MA  01740               ftp:   //ftp.ultranet.com/pub/berlin/


