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Video Processor Module (Continued)

6.2

FUNCTIONAL DESCRIPTION

To understand why the Video Processor functions as it

does, it is first important to understand the difference

between video and graphics. Video is pictures in motion,

which usually starts out in an encoded format (i.e.,

MPEG2, AVI, MPEG4) or is a TV broadcast. These pic-

tures or frames are generally dynamic and are drawn 24 to

30 frames per second. Conversely, graphic data is rela-

tively static and is drawn - usually using hardware acceler-

ators. Most IA devices need to support both video and

graphics displayed at the same time. For some IA devices,

such as set-top boxes, video is dominant. While for other

devices, such as consumer access devices and thin cli-

ents, graphics is dominant. What this means for the Video

Processor is that for video centric devices, graphics over-

lays the video; and for graphics centric devices, video over-

lays the graphics.

Video Support

The SC2200 gets video from two sources, either the VIP

block or the GX1 module’s video frame buffer. The VIP

block supports the CCIR-656 data protocol. The CCIR-656

protocol supports TV data (NTSC or PAL) and defines the

format for active video data and vertical blanking interval

(VBI) data. Conforming CCIR-656 data matches exactly

what is needed for a TV: full frame, interlaced, 27 MHz

pixel clock, and 50 or 60 Hz refresh rate. Full frame pixel

resolution and the refresh rate depends on the TV stan-

dard: NTSC, PAL, or SECAM.

If the VIP input data is full frame (conforming data), the

data can go directly from the VIP block to the Video For-

matter. This is known as Direct Video mode. In this mode,

the data never leaves the Video Processor module. Direct

Video mode can only be used under very specific condi-

tions which will be explained later. If the VIP data is less

than full frame (non conforming data), the VIP block will

bus master the video data to the GX1 module’s video

frame buffer. The GX1 module’s display controller then

moves the video data out of the video frame buffer and

sends it to the Video Formatter. Using this method the tem-

poral (refresh rate) and/or spatial (image less then full

screen) differences between the VIP data and the output

device are reconciled. This method is known as Capture

Video mode. How each mode is setup and operates is

explained further in Section 6.2.1 on page 319.

VBI Support

VBI (vertical blanking interval) data is placed in the video

data stream during a portion of the vertical retrace period.

The vertical retrace period physically consists of several

horizontal lines (24 for NTSC and 25 for PAL systems) of

non-active video. Data can be placed on some of these

lines for other uses.

The active video and vertical retrace period horizontal lines

are logically defined into 23 types: logical line 2 through

logical line 24 (no logical line 1). Logical lines 2 through 23

occur during the vertical retrace period and logical line 24

represents all the active video lines. Logical lines 10

through 21 for NTSC and 6 through 23 for PAL are the

nominal VBI lines. The rest of the logical lines, 2 through 9,

22, and 23 for NTSC and 2 through 6 for PAL occur during

the vertical retrace period but do not normally carry user

data. An example of VBI usage is Closed Captioning,

which occupies VBI logical line 21 for NTSC. Figure 6-2

and Figure 6-3 on page 318 show the (relationship

between the) physical scan lines and logical scan lines for

the odd andevenfieldsinthe NTSC format.

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