RIVA128 datasheet(46/77 Pages) STMICROELECTRONICS

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128-BIT 3D MULTIMEDIA ACCELERATOR

RIVA 128

46/77

8.5

VBI HANDLING IN THE VIDEO PORT

RIVA 128 supports two basic modes for VBI data

capture. VBI mode 1 is for use with the Philips

SAA7111A digitizer, VBI mode 2 is for use with the

Samsung KS0127 digitizer.

In VBI mode 1, the region to be captured as VBI

data is set up in the SAA7111A via the serial inter-

face, and in the RIVA 128 under software control.

The SAA7111A responds by suppressing genera-

tion of SAV and EAV codes for the lines selected,

and sending raw sample data to the port. The

RIVA 128 Video Port capture engine starts captur-

ing VBI data at an EAV code in the line last active

and continues to capture data without a break until

it detects the next SAV code. VBI capture is then

complete for that field.

In VBI mode 2, the region to be captured as VBI

data is set up in a similar manner. The KS0127 re-

sponds by enabling VBI data collection only during

the lines specified and framed by normal ITU-R-

656 SAV/EAV codes. The RIVA 128 Video Port

capture engine starts capturing data at an SAV

code controlled by the device driver, and contin-

ues capturing data under control of SAV/EAV

codes until a specific EAV code identified by the

device driver is sampled. VBI capture is then com-

plete for that field. The number of bytes collected

will vary depending on the setup of the KS0127.

8.6

SCALING IN THE VIDEO PORT

The RIVA 128 Video Port allows any arbitrary

scale factor between 1 and 31. For best results the

scale factors of 1, 2, 3, 4, 6, 8, 12, 16, and 24 are

selected to avoid filtering losses. The Video Port

decimates in the y-direction, dropping lines every

few lines depending on the vertical scaling factor.

The intention is to support filtered downscaling in

the attached video decoder.

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