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Video Processor Module (Continued)

Figure 6-5. Capture Video Mode Bob Example Using One Video Frame Buffer

Weave

The Weave method assembles the odd field and even field

together to form the complete frame, and then renders the

“weaved” frames to the display device. The Video data is

converted from interlaced to progressive. Since both fields

are rendered simultaneously, the GX1 module’s video

frame buffer must be at least double buffered. The Weave

method has the advantage of not creating the temporal

effects that Bob does. The disadvantage of Weave is twice

as much data is transferred from the video frame buffer to

the Video Processor; meaning that Weave uses more

memory bandwidth.

Figure 6-6 on page 322 is an example of the Weave

method in action. As in the Bob example (Figure 6-5), a

CRT monitor at 85 Hz refresh is assumed. Double buffering

of the incoming data is also assumed. The example does

not assume anything about any scaling that may be done in

the Video Processor. No attempt has been made to assure

that this example is absolutely workable. The example is

only presented to allow for a general understanding of how

the SC2200’s video support hardware works.

The following procedure is an example of how to create the

Weave method. Since at least double buffering is required,

more of the VIP’s control registers are used for Weave than

required for Bob during video runtime.

Program the VIP bus master address registers.

Three registers control where the VIP video data is

stored in the GX1 module’s frame buffer:

– F4BAR2+Memory Offset 20h – Video Data Odd

Base Address

– F4BAR2+Memory Offset 24h – Video Data Even

Base Address

– F4BAR2+Memory Offset 28h – Video Data Pitch

The Video Data Even Base Address must be sepa-

rated from the Video Data Odd Base Address by one

horizontal line. The Video Data Pitch register must be

programmed to one horizontal line.

Program other VIP bus master support registers.

Ensure the VIP FIFO Bus Request Threshold is set to

32 bytes (F4BAR2+Memory Offset 00h[22] = 1) and

the Video Input Port mode is set to CCIR-656

(F4BAR2+Memory Offset 00h[1:0] = 10). An interrupt

needs to be generated so that the GX1 module’s video

frame buffer pointer can flip to the field that has com-

pleted transfer to the video frame buffer. So the Field

Interrupt bit (F4BAR2+Memory Offset 04h[16] = 1).

must

enabled.

Auto-Flip

normally

set

(F4BAR2+Memory Offset 04h[10] = 0) to allow the

CCIR-656 decoder to identify which field is being pro-

cessed. Capture video data needs to be enabled

(F4BAR2+Memory Offset 04h[10] = 1) and Run Mode

Capture is set to Start Capture (F4BAR2+Memory Off-

set 04h[1:0] = 11) at beginning of next field. Data is

now being captured to the frame buffer.

Video Data Odd Base

Video Data Even Base

DC_VID_ST_OFFSET

Odd

Field

Even

Field

GX1 Module’s Video Frame Buffer

123456789

9 10 11 12 13 14 15 16 17 18 19 20

22 23

Capture video fill

Video subsystem

85 frames per second

30 frames per second

(F4BAR2+Memory Offset 24h)

Address not changed during runtime

(GX_BASE+Memory Offset 8320h)

Ping-pongs between the two buffers during runtime

(F4BAR2+Memory Offset 20h)

Address not changed

during runtime

Buf #1

sequence

empty sequence

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