User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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These registers determine the characteristics of the gamma correction for the overlay data. Each register

is 32 bits wide. The registers are written to and read from together when accessed from the PCI.

The GAMCxx registers are not double buffered and should only be updated when the Overlay Engine is

disabled. During operation, the bytes of these registers are read independently. These registers are

dependent on the R, G, or B pixel values.

There are several restrictions when using gamma values. The restrictions are:

• Gamma curve should be always a rising curve

• GAMC0 cannot have value of 0

• Difference between the two adjacent gamma registers cannot be greater than 0x7F

31 24 23 16 15 8 7 0

Reserved Red Green Blue

Bit Description

31:24 Reserved.

23:16 Red.

15:8 Green.

7:0 Blue.

GAMC5: Used of bit <7:6> = 11

GAMC4: Used of bits <7:6> = 10

GAMC3: Used of bits <7:6> = 01

GAMC2: Used of bits <7:5> = 001

GAMC1: Used of bits <7:4> = 0001

GAMC0: Used of bits <7:3> = 00001