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Integrated Functions (Continued)

4.4.2

Master/Slave Registers

When starting a BitBLT or vector operation, the graphics

pipeline registers are latched from the master registers to

the slave registers. A second BitBLT or vector operation

can then be loaded into the master registers while the first

operation is rendered. If a second BLT is pending in the

master registers, any write operations to the graphics pipe-

line registers will corrupt the values of the pending BLT.

Software must prevent this from happening by checking the

“BLT Pending” bit in the GP_BLT_STATUS register

(GX_BASE+820Ch[2]).

Most of the graphics pipeline registers are latched directly

from the master registers to the slave registers when start-

ing a new BitBLT or vector operation. Some registers, how-

ever, use the updated slave values if the master registers

have not been written, which allows software to render suc-

cessive primitives without loading some of the registers as

outlined in Table 4-20.

4.4.3

Pattern Generation

The graphics pipeline contains hardware support for 8x8

monochrome patterns (expanded to two colors), 8x8 dither

patterns (expanded to four colors), and 8x1 color patterns.

The pattern hardware, however, does not maintain a pat-

tern origin, so the pattern data must be justified before it is

loaded into the GX1 processor’s registers. For solid primi-

tives, the pattern hardware is disabled and the pattern color

is always sourced from the GP_PAT_COLOR_0 register

(GX_BASE+8110h).

Table 4-20. Graphics Pipeline Registers

Master

Function

GP_DST_XCOOR

Next X position along vector.

Master register if written, otherwise:

Unchanged slave if BLT, source mode = bitmap.

Slave+width if BLT, sourcemode= text glyph

GP_DST_YCOOR

Next Y position along vector.

Master register if written, otherwise:

Slave +/- height if BLT, source mode = bitmap.

Unchanged slave if BLT, source mode = text glyph.

GP_INIT_ERROR

Master register if written, otherwise:

Initial error for the next pixel along the vector.

GP_SRC_YCOOR

Master register if written, otherwise:

Slave +/- height if BLT, source mode = bitmap.

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