Channel Status Decoding
9-20 ADSP-21368 SHARC Processor Hardware Reference
Compressed or Non-Linear Audio Data
The AES3/SPDIF receiver is required to detect compressed or non-linear
audio data according to the AES3, IEC60958, and IEC61937 standards.
Bit 1 of byte 0 in the DIR_B0CHAN register indicates whether the audio data
is linear PCM, (bit 1 = 0), or non-PCM audio, (bit 1 = 1). If the channel
status indicates non-PCM audio, the DIR_NOAUDIO bit flag is set. (This bit
can be used to generate an interrupt.) The DIR_VALID bit (bit 3 in the
DIRSTAT register) when set (=1) may indicate non-linear audio data as well.
Whenever this bit is set, the VALIDITY bit flag in the SPDIF_RX_STAT regis-
ter is also set.
The MPEG-2, AC-3, DTS, and AAC compressed data may be transmitted
without setting either the DIR_VALID bit or bit 1 of byte 0. To detect this
data, the IEC61937 and SPMTE 337M standards dictate that there be a
96-bit sync code in the 16-, 20- or 24-bit audio data stream. This sync
code consists of four words of zeros followed by a word consisting of
0xF872 and another word consisting of 0x4E1F. When this sync code is
detected, the DIR_NOAUDIO bit flag is set. If the sync code is not detected
again within 4096 frames, the DIR_NOAUDIO bit flag is deasserted.
The last two words of the sync code, 0xF872 and 0x4E1F, are called the
preamble-A and preamble-B of the burst preamble. Preamble-C of the
burst preamble contains burst information and is captured and stored by
the receiver. Preamble-D of the burst preamble contains the length code
and is captured by the receiver. Even if the validity bit or bit 1 of byte 0
has been set, the receiver still looks for the sync code in order to record the
preamble-C and D values. Once the sync code has not been detected in
4096 frames, the preamble-C and D registers are set to zero.
L
The SPDIF receiver supports the DTS stream. The DTS specifica-
tions support frame sizes of 256, 512, 1024, 2048 and 4096. The
on-chip SPDIF receiver supports the 256, 512 and 1024 DTS
frames. The DTS test kit frames with 2048 and 4096 frame sizes
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