Switch User Manual

Functional Description
D15343-003 141
Following conditions should be met for the sync (HSYNC, VSYNC) and blank (HBLANK,
VBLANK) signals:
• Start of H(V)SYNC can not coincide with start of H(V)BLANK
• H(V)SYNC should always start after H(V)BLANK starts.
In interlaced mode, the Vertical Total (VTOTAL_A register bits 27:16), Vertical Blank End
(VBLANK_A register bits 27:16), Vertical Sync Start (VSYNC_A register bits 11:0) and Vertical
Sync End (VSYNC_A register bits 27:16) must be programmed to a value 1 less than that of
progressive case, which is described in Section 4.5. For example, for VBLANK end at line 525,
program the register (VBLANK_A register bits 27:16) as 523 (note that it is 524 for progressive
case). This is needed as the line counter is stalled for one line when the Vsync assertion is shifted
between field1 and field2.
6.5.2 Blend Function
The blending unit is responsible for combining display planes onto a display pipe. This is done
using an alpha blending technique that is described as "pre-multiplied source over destination" or a
simple mux operation.
6.5.3 Interlaced Video Field display
The Intel
®
82854 GMCH provides interlace timing support for only Plane A and the Video
Overlay window. Interlace timing is not available for Plane B, Plane C, Hardware Cursor A,
Hardware Cursor B and the VGA plane. The Pipe A timing generator provides the interlace timing
for Plane A and the Video Overlay.
6.5.3.1 Interlace support for Plane A graphics
In the Intel
®
82854 GMCH, all the graphic features in Native Graphic mode are supported in Plane
A, under progressive mode.
In interlace mode, support for Field1 and Field2 timing generation is supported by Plane A. Plane
A makes use of the DPODPfieldID signal generated by the Pipe A timing generator to synchronize
the field timing. This signal is used to indicate which field of the picture should be scanned out.
When DPODPfieldID is high, Field1 is scanned out. The DPODPfieldID is used to set the vertical
line counters to the first line. The counters then increment by two until the end of the field is
reached. During the VBI interval, the DPODPfieldID transitions to low indicating that Field2 is
being processed next. This sets the vertical line counters to the second line and Field2 is then
scanned out.