10-16
Audio Decoder Module
10.5.2 Synchronization
The Preparser in the Channel Interface substitutes the original
substream Linear PCM ID with an 8-byte sync word to mark the
beginning of each Linear PCM packet. The Linear PCM Decoder
searches for and synchronizes to the sync word. If the decoder loses
synchronization, it sets the Audio Sync Error Interrupt bit in Register 4
(
page 4-8
), asserts INTRn to the host if the interrupt is not masked,
mutes the audio output, and searches for the next sync word.
Figure 10.5 Linear PCM Audio Sample Syntax
Linear PCM bitstream samples can be 16, 20 or 24 bits as shown in
Figure 10.5
. Twenty or 24-bit samples are divided into the upper 16 bits
and the lower 4 or 8 bits. The output PCM samples to the DAC interface
can be 16, 20, or 24 bits in length. On the other hand, the S/P DIF
interface accepts only 16-bit samples. The last 4 or 8 bits of 20- or 24-bit
samples are truncated for the S/P DIF interface.
The host can override the bitstream sample resolution for the decoder by
setting the Overwrite Quantization bit in Register 366 (
page 4-89
) and
programming the Host Quantization bits in the same register for 16-,
20-, or 24-bit samples. The decoder truncates or extends the samples
accordingly.
S_2n
S_2n+1
A_2n
(ch 0)
B_2n
(ch 1)
16 bits
MSB
LSB
(ch 3-7)
E_2n
E_2n+1
a_2n b_2n
(ch 0)
4 bits(20-bit mode)
/8 bits(24-bit mode)
MSB
LSB
(ch 3-7)
16-bit mode
20-bit/24-bit mode
The lower 4 or 8 bits of
sample data of each channel
The upper 16 bits of sample of each channel
(ch 1)
H_2n
(ch 8)
h_2n
(ch 8)