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AMD Geode™ SC3200 Processor Data Book 311
Video Processor Module
32581C
7.2 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 accelera-
tors. 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 clients,
graphics is dominant. What this means for the Video Pro-
cessor is that for video centric devices, graphics overlays
the video; and for graphics centric devices, video overlays
the graphics.
Video Support
The SC3200 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 temporal (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
7.2.1 on page 313.
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 7-2
and Figure 7-3 on page 312 show the (relationship
between the) physical scan lines and logical scan lines for
the odd and even fields in the NTSC format.