AMD Geode LX 800@0.9W - Manual (Page 262)

262 AMD Geode™ LX Processors Data Book
Graphics Processor Register Definitions 33234H
6.4.2.7 Source Color Foreground (GP_SRC_COLOR_FG)
When source data is monochrome, the contents of this register are used for expanding pixels that are set in the mono-
chrome bitmap, thus replacing the monochrome bit with a color that is appropriately sized for the destination.
When source data is color, this register contains the color key for transparency. The value(s) in this register is XOR’ed with
the color source data, after which the GP_SRC_COLOR_BG register (GP Memory Offset 14h) is used to mask out bits that
are don’t cares. If all bits of a pixel that are not masked off compare, and source transparency is enabled, then the write of
that pixel will be inhibited and the frame buffer data will be unchanged. Otherwise, the frame buffer will be written with the
color data resulting from the raster operation.
If no source is required for a given BLT, the value of this register is used as the default source data into the raster operation.
This register should only be written after setting the bpp in GP_RASTER_MODE (GP Memory Offset 38h), since the value
written is replicated as necessary to fill the register. Thus a write to this register in 8-bpp mode takes the least significant
data byte and replicates it in the four bytes of the register. In 16-bpp mode, the least significant two bytes are replicated in
the upper half of the register. A read returns the replicated data.
GP Memory Offset 10h
Type
R/W
Reset Value 00000000h
GP_SRC_COLOR_FG Register Map
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
SRC _FG
GP_SRC_COLOR_FG Bit Descriptions
Bit Name Description
31:0 SRC_FG Source Foreground.
Mono source mode: Foreground source color.
Color source mode: Color key for transparency.