1. EE 4993 Display Drivers in NT
Bob Reese

2. Graphics Hardware Course Goals
Understand the basics of Graphics operations.
How can you understand how to build hardware
if you don’t understand the problem?
Understand the OS interface to Graphics Hardware.
You need to be able to make the hardware useful
inside of some operating system.
Understand Graphics Hardware Implementation.
Graphics needs hardware assistance in order
to meet today’s performance expectations - how
is this done?

3. Graphics Hardware Course Implementation
Understand the basics of Graphics operations.
Prof. Moorhead will cover basic graphics operations,
concentrating at the raster-level
Understand the OS interface to Graphics Hardware.
We will look at device driver interfaces for graphics
accelerators under WinNT; will study some sample
code.
Understand Graphics Hardware Implementation.
Will look at a couple of case studies; perhaps do
some VHDL implementation of a couple of 2D
raster algorithms. Will study mostly 2D, touch on
3D.

4. What is a Device Driver (DD)?
A Device Driver is a piece of code that manages some
peripheral device.
Users do not access a DD directly; Users make calls
to some OS-defined Application Programming
Interface (API). The API will then end up calling
the Device Driver. This makes the user code
independent of the Device Driver code.
The Hardware Vendor writes the device driver. The
device driver must supply some set of function calls
to be used by the OS. This set of function calls
is known as the Device Driver Interface (DDI).

5. Graphics System Architecture - WinNT 4.0
Note that 3 interfaces access the Graphics Hardware

6. Software Interfaces for Graphics Hardware under WinNT
GDI / DDI
Used by any software that uses Win32 APIs
(before Direct Draw, this meant ALL software).
All graphics acceleration is 2D; benchmarks for
this interface measure graphics performance for
business software (spreadsheets, word processing,
window management, etc).
Direct Draw / DD Hardware Abstraction Layer (HAL)
New API from Microsoft for game programming, HAL
offers ‘thinner’ layer between DD API and hardware.
Supports both 2D and 3D acceleration
OpenGL
Graphics API from Silicon Graphics that offers access
to both 2D and 3D acceleration. Compete directly with
Direct Draw API.

7. Application, GDI, Device Driver Interaction
GDI stands for Graphical Device
Interface. Parts operate in both
user mode and kernel mode
DDI stands for Device Driver
Interface. The DDI operates
in kernel mode.
Note that the Device driver (Graphics Driver) can call GDI functions - allows for the DD to take advantage of functionality in the GDI

8. Another View of the GDI / DDI Interaction
Application
Subsystem
Win32 Subsystem
handle ("video" file object)
user mode
kernel mode
System Services
I/O Manager
DDI drivers
GDI
display
IoXxx
EngXxx
driver
support routines
routines
video port driver's
VideoPortXxx
video
miniport driver
video adapter
system hardware
frame buffer
2vidlayr

9. Division of Responsibilities
GDI
Provides software rendering support for Win32 GDI
calls. Creates graphics objects for use by Device
Driver.
Device Driver
Talks to graphics hardware; accesses graphics
acceleration features. Can make use of GDI services
for managing graphics Objects created by GDI.
Video Port Driver/ Video MiniPort
Two tightly coupled drivers; Video Port Driver is
generic and provided by Microsoft. Video Miniport
talks to Video Port Driver and handles device-specific
functions such as graphics hardware initialization,
cursor or pointer hardware on video card, mode-set and
palette operations for MS-DOS sessions.

10. More on the Differences between DD and Miniport
Both the DD and Miniport access the hardware.
The miniport is intended to be paired one-on-one
with a particular variation of video card. As such,
one of the jobs of the miniport is to return video
card configuration information to the display driver.
The number of required functions in the miniport
is low which keeps the miniport code size small.
The required display driver code is more complex
than the miniport code and can work across a
family of video cards. The DD can call functions in
the GDI to return configuration info from the miniport.
EXAMPLE : Matrox Millenneium I & II, Matrox Mystique
The same display driver (Mga64.dll) is used for
all three of these cards. However, there are different
miniports (mga_mil.sys) for each particular card.

11. One more Picture….

12. Device Driver Development under WinNT
SDK For WinNT
The WinNT Software Developers Kit (SDK) provides
libraries and C/C++ Header file for doing general
WinNT system development.
From the ‘Start’ menu, look for topics labeled
Win32 SDK
DDK For WinNT
The WinNT Device Driver Kit provides an environment
for building (compile/link) and debugging device
drivers. It also provides sample code for different
driver types.
From the ‘Start’ Menu, look for topics labeled
Windows NT DDK

13. DDK Directory Structure
inc - include directory which contains
all system header files.
lib - compiled dll files are placed here
src - source code examples for different
driver types are contained here. We
will be interested in the directory tree:
src\video\displays\mga
which contains a sample display driver
for the Matrox Millenneium I.
Also,
src\video\miniport
contains source code for video miniport
drivers.

14. Interesting Files in src/displays/mga
enable.c specifics to GDI what functions will be hardware assistant
driver.h data structures used by driver code.
ddk/inc/windi.h general GDI/DDI definitions
bitblt.c highlevel bitblt interface code to GDI
bltmga.c low level bitblt code for MGA Millenenium
(actually, for all of this family except for ‘Storm’).
hw.h hardware definitions (registers, bitmasks, etc)
ddraw.c support for Direct Draw
MCD*.c many files to implement OpenGL mini client driver.

15. To Build the MGA display driver
1. Execute
Start > Programs > WinNT DDK > Checked Build
2. You will be in the C:\DDK directory. cd to src\video\displays\mga
3. Type ‘build’ - this will compile all files. ‘.obj’ files will go in the obj\i386 directory.
The mga.dll will be placed in the
c:\ddk\lib\i386\checked
directory.
4. To install, you must be on a system that has
the Matrox Millennenium I card. Copy the mga.dll file to the c:\winnt\system32 directory. Before copying, make a copy of the old driver. Reboot the machine to test the new driver.

16. What will we try to learn about Device Drivers?
It is a big topic!!
Lots of complicated code; will try to get feel for the
GDI/DirectDraw/OpenGL interfaces to the hardware.
BitBlts
BitBlts are very important for 2D performance. We
try to look at this code in some detail. For 3D, still
to be decided.
Performance/Capability
Will look at standard ways for testing performance and capability of graphics display drivers by looking at the Microsoft Hardware Compatibility Tests and the Ziff-Davis Benchmarks.
Debugging
Will look at Device Driver debugging using WinDBG.

17. GDI / DDI
Capabilities
In graphics display driver speak, capabilities refers
to the list of graphics operations which a device
driver will handle rather than letting the system
perform the operation. The GDI will query the
display driver for its capabilities. This is necessary because different graphics adapters will be able to handle different sets of operations.
Performance
If a display driver elects to handle an operation such
as a BitBlt, then it should do so at faster performance than the what the system can provide. Usually, the display driver will handle the operation
only if hardware assistance is provided.

18. GDI / DDI (cont.)
Hooking, Punting
Electing to handle a drawing function in the display
driver is known as hooking. When a call is hooked,
ie., DrvBitBlt (does a BitBlt), the GDI will call the
driver to handle this operation. However, the driver does not handle to all cases. The driver can check
for the cases it does handle (e.g., all BitBlts except
for 24-bit color cases) and if it can’t handle the call, the driver can punt the call back to the GDI. The GDI
will then do the operation.
DrvBitBlt versus EngBitBlt
As an example, the DrvBitBlt call is the bitblt operation done via the display driver. The EngBitBlt
call is the GDI simulation of this operation.

19. Display Driver Exercise #1
Determine Performance difference between hardware
accelerated BitBlt and GDI-emulated BitBlt
Need a Benchmark for 2D Graphics - Use the
Ziff Davis WinBench 98 benchmarks
Ziff Davis WinBench 98
Under WinBench 98, many different tests can be
run:
Disk, Business Graphics, Direct Draw, Video….
We will be interested in the Business Graphics since
these basically measure GDI32 2D graphics performance.

20. Display Driver Exercise #1 (cont)
The mga driver supplied in the DDK hooks the BitBlt operation from the GDI.
Read the DDK documentation and determine how to unhook the BitBLT operation
(hint: you will have to modify enable.c ).
Use the Business Graphics WinMark 98 test under
WinBench 98 to measure the resulting performance
with BitBLT being performed by the GDI.
When you run the Graphics WinMark, you will get a
warning about some ‘unnecessary processes’ currently
executing; don’t worry about this. You may also have
to turn off the ‘always on top’ flag on the bottom taskbar
in order for the benchmark to run.

21. Business Graphics Results
200 Mhz Pentium, MGA checked build, Hardware BitBlt, NT 4.0
Units are in Million Pixels/sec

22. What from GDI can be accelerated by Display Driver?
BitBlt, Stretched BitBlt
A stretched BitBlt is when the destination rectangle
is not the same size as the source rectangle
Pointer Management
Can also be accelerated via Video miniport.
Line Drawing
General Path Drawing/Filling (this means curves and lines)
Memory Transfers
Text output

23. Device Driver Debugging
Debugging a Device Driver, especially a display driver,
is difficult.
A program called WinDBG is used for this purpose.
Null Modem Cable
Target Host
DD to be debugged is on Target. Host runs WinDBG.
Special NT boot option on Target enables debug info
to be sent to Host via serial Port.

24. WinDBG Capabilities
Via WinDBG, you can:
Set a break point in a DD
Single Step a DD
Watch order in which systems DDs are being loaded
Examine Memory areas
Data display in WinDBG is limited to Hex memory dumps (YAARRRRG). However, you add ‘extension functions’ to WinDBG via user DLLs. These extension functions are mostly used to print out various data structures when passed an address.
You will become very familiar with WinDBG……..