BT848 ETC, BT848 Datasheet - Page 65

• Manufacturer Part Number: BT848
• Description: Single-Chip Video Capture for PCI
• Manufacturer: ETC

Bt848/848A/849A
Single-Chip Video Capture for PCI
Figure 24. Example of Bt848 Performing Complex Clipping
Brooktree
Complex Clipping
®
Y
Cr
Cb
Write #Bytes @ Line 0
...
Write #B @ L40, Skip #B, Wr #B @ L40
...
SYNC VRO
Write123 #B @ Y, #B @ Cr, #B @ Cb
...
SYNC VRE
JUMP
CPU
System DRAM
It is necessary to be able to clip the video image before it is put onto the PCI bus
when writing video data directly into on-screen display memory. The Bt848 sup-
ports complex clipping of the video image for those applications which require the
displayed video picture to be occluded by graphics objects such as pull-down
menu, overlaying graphics window, etc. Typically, a target graphics frame buffer
controller cannot provide overlay control for the video pixel data stream when it
being provided by a PCI bus master peripheral to the graphics PCI host interface.
onto the PCI bus in the areas where graphics are to be displayed, that is, where
graphics objects are “overlaying” the video image. The Bt848 cuts out portions of
the video image so that it can “inlay” or fit around the displayed graphics objects.
(DDI) provider to the Bt848 device driver software to indicate the areas of the dis-
play where the video image is to be occluded. The Bt848 driver software interprets
the clip list and generates a RISC program that blocks writing of video pixels that
are to be occluded. This is illustrated in Figure 24.
Bridge
Host
The Bt848 implements clipping by blocking the video image as it is being put
A clip list is provided through the graphics system DirectDRAW Interface
Even Field Prog
Planar 4:2:2
Odd Field Prog
Packed RGB
L848A_A
Bt848
Graphics Controller
Video in a Window
Frame Buffer
Dialog
Box
F
PCI Bus
UNCTIONAL
DMA Controller
D
ESCRIPTION
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