WM8850
Pre-Production
Loss of Lock
Should the S/PDIF Rx lose lock, an unsolicited response will be triggered to indicate the change in
lock status. The data in the link sample blocks will be set to 0, and the stream will continue to run at
the previously recovered sample rate. There may be several samples of data before the unsolicited
response can be sent, but the data will be zeroed immediately.
If the S/PDIF Rx is in Software Formatted S/PDIF mode, and the loss of lock event occurs, all 32-bits
of the data are zeroed.
Change in Sample Rate
Once a stream has started, stream parameters such as sample-size, number of channels, and
sample rates should not be changed. For the S/PDIF Rx audio path, it is expected that any change of
S/PDIF sample rate will cause the S/PDIF Rx to lose lock.
Once the S/PDIF Rx has gained lock to the new sample rate (or regained lock at the existing sample
rate), the controller will be sent an unsolicited response.
The S/PDIF Rx audio path has two methods of handling the relock condition:
1. Push Method: where upon lock, the stream (assuming SRC1 is bypassed) immediately
changes sample rate to the new recovered rate, and data is no longer overwritten with
zeros.
2. Controlled Method: where zeroed data continues to be transmitted at the old sample rate,
until the stream ID is set to 0. Upon re-assignment of the Stream ID, non-zeroed stream
data is transmitted at the newly recovered sample rate.
These methods are selected using the Unlock Ctrl register in the SPDIF_IN Control Verb.
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 WM8850. 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.
Channel synchronisation between channels is only guaranteed where stream packets are received by
the WM8850 after all converters in a multi-channel stream have had their stream ID assigned.
PP, April 2011, Rev 3.2
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
