VT8601 Via, VT8601 Datasheet - Page 122

• Manufacturer Part Number: VT8601
• Description: Slot-1 / Socket-370 PCI North Bridge
• Manufacturer: Via

Graphics Engine Organization
The ProMedia Graphics Engine consists of the following
units: Setup Engine, Rasterization Engine, and Pixel Engine.
These units are organized as follows:
The interfaces among the components are:
Each unit performs the following functions:
Revision 1.3 September 8, 1999
AGP to Pixel Engine: Set drawing environment registers.
AGP to Rasterization Engine: Set primitives: edge
walking, slopes.
AGP or Setup Engine: Set vertices, culling info.
Setup Engine to Rasterization Engine: Set primitives:
edge walking, slopes.
Rasterization Engine to Pixel Engine: Pixel Data,
addresses and coordinates.
Pixel Engine to Memory Interface: Addresses and
coordinates, pixel data.
Setup Engine: Back face culling, slope calculation.
Rasterization Engine: Edge walking, color interpolation,
Z, texture coordinates, perform perspective correction.
Pixel Engine: Generate addresses and coordinate for all
memory accesses:
source/destination, write destination (draw buffer), 2-D
functions,
modulation, ROP, Z test, alpha test, transparency, etc.
7HFKQRORJLHV ,QF
:H &
:H &R R QQHFW
Pixel Engine
QQHFW
bi/tri-linear
Rasterization Engine
Memory Interface
read/write Z, read texture, read
A G P
interpolation,
Setup Engine
blending
and
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When the Setup Engine is to be used, the following steps
should be taken to perform drawing functions:
Triangles sent to the Setup Engine can be interleaved with
primitives sent to the Rasterization Engine in step 3 above.
The Setup Engine uses the same sequential loading
mechanism as in the Rasterization Engine.
loading is: Triangle Attribute, Vertex 0, Vertex 1 (optional),
Vertex 2 (optional). Whether vertex 1 and 2 are to be loaded
depends on the Primitive Type. Writing to BA+4Ch triggers a
loading sequence to the Setup Engine. The order of data in a
vertex is: RGBA, SrgbF, W, UV, Z, XY. Not every one will
appear in every vertex. Whether a particular item will be
present in a vertex is decided by the Triangle Attribute. For
example, the data in a stream for a texture mapped triangle
strip may look like: Triangle Attribute, U0V0, X0Y0.
GEbase + 2C – Setup Engine Status ................................. RO
This register records setup engine overflow status. For every
triangle, the entire register is shifted left one bit with bit-0 then
set to reflect whether the triangle has slope overflow. This
register is usefuil for debugging purposes.
resides in the VGA address space and is not decoded by the
setup engine.
31-0 Overflow Status
S/W sets up the drawing environment.
S/W issues a drawing command.
S/W continuously sends triangles to the Setup Engine (or
primitives to the Rasterization Engine).
S/W sends a triangle with last flag set or a null triangle to
the Setup Engine to signal the end of the operation (or its
equivalent to the Rasterization Engine).
VT8601 Apollo ProMedia
3D Graphics Engine Registers
The order of
This register