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Integrated Functions (Continued)

4.4

GRAPHICS PIPELINE

The graphics pipeline of the GX1 processor contains a 2D

graphics accelerator. This hardware accelerator has a Bit-

BLT/vector engine which dramatically improves graphics

performance

when

rendering

and

moving

graphical

objects. Overall operating system performance is improved

as well. The accelerator hardware supports pattern gener-

ation, source expansion, pattern/source transparency, and

256 ternary raster operations. The block diagram of the

graphics pipeline is shown in Figure 4-11.

4.4.1

BitBLT/Vector Engine

BLTs are initiated by writing to the GP_BLT_MODE regis-

ter, whichspecifies thetypeofsourcedata(none, frame

buffer, or BLT buffer), the type of the destination data

(none, frame buffer, or BLT buffer), and a source expansion

flag.

Vectors are initiated by writing to the GP_VECTOR_MODE

of the vector and a “read destination data” flag.Ifthe flag is

set, the hardware will read destination data along the vec-

tor and store it temporarily in the BLT Buffer 0.

The BLT buffers use a portion of the L1 cache, called

“scratchpad RAM”, to temporarily store source and destina-

tion data, typically on a scan line basis. See Section 4.1.4.2

“Scratchpad RAM Utilization” on page 100 for an explana-

tion of scratchpad RAM. The hardware automatically loads

frame-buffer data (source or destination) into the BLT buff-

ers for each scan line. The driver is responsible for making

sure that this does not overflow the memory allocated for

the BLT buffers. When the source data is a bitmap, the

hardware loads the data directly into the BLT buffer at the

beginning of the BLT operation.

Figure 4-11. Graphics Pipeline Block Diagram

Pattern

Hardware

Raster Operation

Output Aligner

PAT

SRC

DST

Internal Bus

Interface Unit

Graphics

Scratchpad RAM

BitBLT Buffers

and

Memory

X-Bus

C-Bus

Pipeline

BE = Byte Enable

PAT = Pattern Data

SRC = Source Data

DST = Destination Data

Output Aligner

Source

Expansion

Control Logic

DRAM Interface

Controller

Key:

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