TMS320AV7110 datasheet(39/131 Pages) TI

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DSP

TMS320AV7110

Revision 3.1

10/08/99 22:18

Page 39

7.7.2 Split Video Input Buffer

It is also possible to split the video input buffer between DRAM and SDRAM to increase the amount of

SDRAM space available for OSD display. When this mode is selected, the DRAM portion is only used

as an overflow buffer. When the allocated buffer space in the SDRAM is full, the incoming data is

written directly to the DRAM. As soon as memory space is available in the SDRAM, the data is

transferred from the DRAM to the SDRAM via DMA automatically. Once the overflow buffer in the

DRAM has been emptied, incoming data is written directly to the SDRAM again. The video decoder

always takes data from the SDRAM. The size of the buffers in each area of memory is under API

control. At least 107 KBytes of the Video Input Buffer must be located in the SDRAM for the video

decoder to operate properly. The minimum total VBV buffer size required from combined SDRAM

and DRAM is 356,376 Bytes. The split should be changed only when the decoder is inactive to avoid

loss of data. A dedicated DMA channel is used for the automatic transfer of data from the DRAM to

SDRAM to implement this split buffer scheme. Table 16 shows the maximum amount of memory (in

bytes) that can be made available for OSD applications when the video input buffer is split off to the

DRAM (1Mbits and 1.5Mbits shown) on the extension bus.

Table 16. Target OSD Memory Space in SDRAM (in Bytes)

Decoder Options

Max OSD space with a 16Mbit SDRAM

internal

display

sync

Video Input Buffer split

SDRAM

DRAM

Letterbox 3/5 ratio

0.78 B frame

Letterbox 3/4 ratio

0.72 B frame

Normal Display

0.6 B frame

356,376

N/A

74,216

YES

356,376

37,241

74,566

149,216

YES

225,304

131,072

168,313

205,638

280,288

YES

159,768

196,608

233,849

271,174

345,824

7.8 Configuration of the Video Decoder

7.8.1 Configuration of video display format

The ‘AV7110 processes video with aspect ratios of 4:3, 16:9, and 2.21:1. It also supports the display

aspect ratio of 4:3 and 16:9. Figure 10 details the various display formats supported by the ‘AV7110,

and the application can select the specific format using API.

The following 3 flags, controlled by the API, are used to define the specific display format.

16:9_DISPLAY:

This flag can only be set during power up; because setting this flag causes an

automatic hardware reset.

0: 4:3 display device, default value

1: 16:9 display device

DIS_PAN_SCAN:

This flag can be set at any time and it takes effect at the next sequence start.

0: [default value] Apply Pan_Scan mode when the source video is 2.21:1,

or when the source video is 16:9 and the display device is specified as 4:3.

1: [Letterbox mode] Selects letterbox display when the source video is 16:9

and the display is 4:3 or when the source video is 2.21 and the display is

16:9. If the source video is 2.21 and the display is 4:3, the specific display

depends on the flag LB_PAN_SCAN

LB_PAN_SCAN:

This flag only applies to the case where the source is 2.21:1 and the output is

4:3

0: letterbox display only, default value

1: apply pan and scan followed by letterbox display

7.8.2 True Size Display Mode

The MPEG-2 bit stream contains two types of image size information; the encoded source image size

and the active display size. Typically, these two sizes are equal. The size information specified by the

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