VT8601 Via, VT8601 Datasheet - Page 125

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

Rasterization Engine Registers
The major responsibilities of the Rasterization Engine are:
In the ProMedia, the Rasterization Engine performs color
(including alpha) interpolation, texture coordinate (perspective
corrected) generation, Z coordinate interpolation, and texture
gradient (perspective corrected) calculations.
Host access to the Rasterization Engine is by sequential writes
to minimize AGP bandwidth requirements. This is not needed
for the Setup Engine to access the Rasterization Engine. In
addition, if sequential parameters were used to interface
between the Setup Engine and the Rasterization Engine, it
would incur extra cost for the Setup Engine to pack data and
would also reduce performance. Therefore, the Setup Engine
accesses working registers in the Rasterization Engine
directly. To synchronize operation, hardware must wait until
the Setup Engine becomes idle to accept data from the host to
the Rasterization Engine.
Revision 1.3 September 8, 1999



Receive data from host: Set registers, sequential loading
of parameters.
Edge walking: Generate end points of polygon edges or
pixels on a line.
Interpolation:
coordinates on a polygon / line.
Perspective correction: Perform perspective correction.
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Calculate values such as texture
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Both Rasterization and Setup Engines share one interface to
the AGP Write Buffer.
Rasterization Engine and Setup Engine use stream decoding to
receive data from the host. Once they are inside a stream,
they must act quickly to grab data to prevent other
components from taking the data.
decoders in the graphics engine is a potential source for
problems. The second reason is that both the Rasterization
Engine and Setup Engine handle the same types of data.
Coupling them tightly makes the design easier and reduces
problems that arise from synchronization. The third reason is
for better synchronization between the two engines.
The engine interfaces to the host through both random access
registers and sequential loading. There are two random access
registers: Primitive Attribute and Primitive Type.
Primitive Attribute register consists of most parameter
information from the Rasterization Engine’s Primitive Type
and the Setup Engine’s Triangle Attribute register.
The address space that can be used by sequential loading
parameters is from Base Address + 40h to Base Address +
FFh. Software should not use addresses outside this space for
parameters. Sequential loading must use the address in this
space starting at 0x40H in ascending order. For example,
the first address must be 40h, the next must be 44h, etc. In
order to give time to notify the other component to stop
decoding, address 40h is exclusively reserved for sequential
loading.
VT8601 Apollo ProMedia
The first reason is that both
3D Graphics Engine Registers
Having two stream
The