AMD SC3200 manual Functional Description, Video Support, VBI Support

Video Processor Module 32581C

7.2Functional 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 7-2and Figure 7-3on page 312 show the (relationship between the) physical scan lines and logical scan lines for the odd and even fields in the NTSC format.

AMD Geode™ SC3200 Processor Data Book 311