AMD SC1201, SC1200 Functional Description, Video Support, VBI Support, Video Processor Module

Video Processor Module 32579B

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 centric devices usually render video full frame. On a TV, the video image is larger than the screen and will actu- ally spill outside or overscan the TV’s viewable area by about 10%. This is done intentionally to eliminate any black border. Consequently graphic overlays, such as menus and control buttons, must account for overscan when displaying on a TV. Conversely, when the output device is a CRT mon- itor or a TFT panel there is no overscan so the graphic overlays do not have to deal with this issue. Common soft- ware drivers can easily support either type of display device.

Graphic centric devices render graphics full frame. Again, if the TV is the output device, overscan comes into play, but the graphic content cannot be allowed into the overscan area. Software drivers and/or applications must take that into account. The video overlay, when it is active, is usually rendered less than full frame. For some IA devices the video and graphics exchange dominance is application- dependent. An example of this is an Internet enabled set- top box where video is dominant during TV viewing and graphics is dominant during Web browsing.

Video Support

The SC1200/SC1201 processor 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 standard: NTSC, PAL, or SECAM.

If the VIP input data is full frame (conforming data) and the output is the TV interface, then the data can go directly from the VIP block to the Video Formatter. This is known as Direct Video mode. In this mode, the data never leaves the Video Processor module. If the output is to a CRT or TFT interface, or the VIP data is less than full frame (non con- forming data), the VIP block will bus master the video data to the GX1 module’s Video Frame Buffer. The GX1 mod- ule’s Display Controller then moves the video data out of the Video Frame Buffer and sends it to the Video Format- ter. 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 315.

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 314 show the (relationship between the) physical scan lines and logical scan lines for the odd and even fields in the NTSC format.

AMD Geode™ SC1200/SC1201 Processor Data Book 313