Intel 815 manual Source Pitch Offset or Monochrome Source Quadwords

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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12.3.12.BR11—BLT Source Pitch (Offset) or Monochrome Source Quadwords

Memory Offset Address:				4002Ch
Default:				None
Attributes:				RO; DWord accessible
31				14	13	0
			Reserved		Source Pitch (Offset) or
					Monochrome Source Quadwords
		Bit		Descriptions
	31:14		Reserved.
	13:0		Source Pitch (Offset) or Monochrome Source Quadwords. When the color source data is located
			within the frame buffer or AGP aperture, these signed 14 bits store the memory address offset (pitch)
			value by which the source address originally specified in the Source Address Register is incremented
			or decremented as each scan line’s worth of source data is read from the frame buffer by the BLT
			Engine, so that the source address will point to the next memory address from which the next scan
			line’s worth of source data is to be read.
			When the source data is provided by IMMEDIATE_BLT instruction, these 14 bits store the number of
			bytes to be counted from the beginning of a scan line’s worth of data to where the next scan line’s
			worth of data begins.
			Note that if the intended source of a BLT operation is within on-screen frame buffer memory, this
			offset is normally set to accommodate the fact that each subsequent scan line’s worth of source data
			lines up vertically with the source data in the scan line, above. However, if the intended source of a
			BLT operation is within off-screen memory, this offset can be set to accommodate a situation in which
			the source data exists as a single contiguous block of bytes where in each subsequent scan line’s
			worth of source data is stored at a location immediately after the location where the source data for the
			last scan line ended.
			When monochrome source data is being processed, this field is used for indicating the total number of
			Quadwords of data in the source data stream.

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