STA310 datasheet(18/90 Pages) STMICROELECTRONICS

18 / 90 page

STA310

18/90

Figure 9.

4.5 Streams parsers

The parsing stage is operated by two parts: the packet parser and the audio parser.

The packet parser unpacks stream, sorts packets and transmit data to the audio parser. The audio parser ver-

ifies the stream syntax, extracts non-audio data and sends audio data to the frame buffer.

Packet parser

Before unpacking packets and transmitting data, the packet parser needs to detect the packet start by recog-

nizing the packet synchronization word. It is possible to force the parser to search for two packet synchronization

words before starting to unpack and transmit.

This is done by setting the register PACKET_LOCK to 1. Otherwise, the packet parser will start handling the

stream once it has detected information matching the packet synchronization word.

The packet parser is also able to perform selective decoding: it can decode audio packets that are matching a

specified Id. This Id is specified in AUDIO_ID and AUDIO_ID_EXt registers, and the function is enabled by set-

ting the AUDIO_ID_EN register.

Audio parser

The audio parser needs to detect the audio synchronization word corresponding to the type of stream that must

be decoded. It is possible to force the audio parser to detect more than one synchronization word before pars-

ing.

This is done by setting the SYNC_LOCK register to a value between 1 and 3 - number of supplementary sync

words to detect before considering to be synchronized.

The status of synchronization of both parsers is provided in the register SYNC_STATUS. Each time the syn-

chronization status of one of the two parsers changes, the interrupt SYN is generated (if enabled) and the status

can be read in SYNC_STATUS.

4.6 Decoding modes

4.6.1 AC-3

The STA310 is Dolby Digital certified for class A products. The decoder must be programmed so to specify the

stream format as AC-3 encoded: register DECODESEL = 0.

In the sections below are provided the modes specific to the AC-3 decoding.

4.6.1.1 Compression modes

Four compression modes are provided in the STA310:

LRCLKIN

DSTR

SIN

Transferred data

Discarded data

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