WM8860 datasheet(29/184 Pages) WOLFSON

29 / 184 page

Pre-Production

WM8860

PP, April 2011, Rev 3.2

SDO

It is possible that the SDO line could be oversubscribed, if all streams are active at their maximum

sample rate, and word length. It is the responsibility of the Controller to handle this situation, and

determine what is put on the SDO line during oversubscription. The WM8860 will produce unsolicited

responses from the converter nodes that have not received the stream packets that they have been

configured for.

SDI

The WM8860 invokes a protection mechanism, should a bandwidth over-subscription situation arise.

The mechanism monitors the sample rate, and sample-size settings of a stream to detect

oversubscription.

If the SDI line is over-subscribed, due to software configuration or configuration from the recovered

S/PDIF sample-rate, the stream (or streams) assigned the highest Stream ID tag value, will be

dropped, and an unsolicited response issued from the stream converter whose stream has been

dropped.

A stream will be restarted on a re-issue of a non-zero stream ID. However, should the bandwidth

problem still be present, the stream won’t start and an unsolicited response will be re-sent.

Although there is a protection mechanism in the WM8860, it is the responsibility of the user to identify

and rectify bandwidth problems.

SOFTWARE FORMATTED (RAW) S/PDIF

An S/PDIF sub-frame consists of a preamble, 24-bits of audio data, and four control bits. In Software

Formatted (Raw) S/PDIF mode, all 24-bits of the audio data, plus the 4 bits of control information,

plus a 4-bit encoding of the preamble (taking the last 4-bits of the 8-bit bi-phase encoded preamble)

are transported across the link. Software Formatted S/PDIF mode is selected by setting the Bits

S/PDIF TX VALIDITY FLAG

The validity flag is bit [28] of an S/PDIF sub-frame. It is configured using V-bit in the Digital Converter

Control Verb.

When the V-bit is set to 1, the validity flag for both sub-frames is set to 1.

When the V-bit is set to 0, the validity flag for both sub-frames is set to 0, unless an invalid sample is

being transmitted for that sub-frame - in which case the validity flag is set to 1 for that sub-frame.

An invalid sample may occur under the following conditions:



The Stream ID is set to 0



SRC2 is enabled but is unlocked



There has been a FIFO overrun/under-run condition in the S/PDIF Tx Stream Manager (i.e.

a Stream Error).

Note: A Stream Error problem would only be present due to a problem upstream of the WM8860. A

Stream Error triggers an unsolicited response with the EF_STREAM_ERR flag set. If an invalid

sample is detected, it will be overwritten with all-zeros if VCFG in the Digital Converter Control Verb is

set to 1.

CHANNEL NUMBERING

Multi-Channel Streams

Channels 0, 2, 4, etc will be assigned to the Left Channel of a stereo converter. Channels 1, 3, 5, etc

will be assigned to the Right Channel of a stereo converter.

WM8860 Datasheet(PDF) 29 Page - Wolfson Microelectronics plc

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