Intel 815 manual Source Select Mode, Dynamic Color Depth

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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Bit	Descriptions
28	Monochrome Pattern Transparency Mode. This bit applies only when the pattern data is
	monochrome. This bit determines whether or not the byte(s) at the destination corresponding to the pixel
	to which a given bit of the pattern data also corresponds will actually be written if that pattern data bit
	has the value of 1. This feature can make it possible to use the pattern as a transparency mask. The
	BLT Engine is configured to accepted either monochrome or color pattern data via the opcode in the
	Opcode and Control register.
	0 = This causes normal operation with regard to the use of the pattern data. Where a bit in the pattern
	data has the value of 0, the color specified in the background color register is used as the pattern
	operand in the bit-wise operation for the pixel corresponding to the pattern data bit, and the bytes
	at the destination corresponding to that pixel are written with the result.
	1 = Wherever a bit in the pattern data has the value of 0, the byte(s) at the destination corresponding
	to the pixel to which the pattern data bit also corresponds are simply not written, and the data at
	those byte(s) at the destination are allowed to remain unchanged.
27	Source Select Mode.
	0 = Configures the BLT Engine to read the source data from the frame buffer at the location specified
	in the Source Address Register.
	1 = Configures the BLT Engine to accept the source data from the instruction stream controller
	through the IMMEDIATE_BLT instruction. The BLT Engine will hang if it does not get an even
	number of DWs.
26	Reserved. Must Be One (‘1’).
25:24	Dynamic Color Depth.
	00 = 8 Bit Color Depth
	01 = 16 Bit Color Depth
	10 = 24 Bit Color Depth
	11 = Reserved
23:16	Raster Operation Select. These 8 bits are used to select which one of 256 possible raster operations is
	to be performed by the BLT Engine. The 8-bit values, and their corresponding raster operations, are
	intended to correspond to the 256 possible raster operations specified for graphics device drivers in the
	Microsoft Windows* environment. The opcode must indicate a monochrome source operand if
	ROP = F0.
15:14	Reserved. Must be Zero.
13:0	Destination Pitch (Offset). These 14 bits store the signed memory address offset value by which the
	destination address originally specified in the Destination Address Register is incremented or
	decremented as each scan line’s worth of destination data is written into the frame buffer by the BLT
	Engine, so that the destination address will point to the next memory address to which the next scan
	line’s worth of destination data is to be written.
	If the intended destination of a BLT operation is within on-screen frame buffer memory, this offset is
	normally set so that each subsequent scan line’s worth of destination data lines up vertically with the
	destination data in the scan line, above. However, if the intended destination of a BLT operation is within
	off-screen memory, this offset can be set so that each subsequent scan line’s worth of destination data
	is stored at a location immediately after the location where the destination data for the last scan line
	ended, in order to create a single contiguous block of bytes of destination data at the destination.

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