GS2971A Datasheet, PDF (90/152 Pages) Gennum Corporation – Integrated audio clock generator

Address 0
5
Read
Pointer
29
35
Audio Buffer
A
B
Write
Pointer
Figure 4-47:Audio Buffer Pointer Boundary Checking
Write
Pointer
The repeat or drop sample operation is performed a maximum of 28 consecutive times,
after which the audio outputs are muted (all sample data set to zero). In SD Mode, 26
samples are required to be written into the FIFO prior to starting the read operation
again.
The audio buffer pointer offset may be reduced from 26 samples to 12 or 6 samples using
the OS_SEL[1:0] bits in the host interface. The default setting is 26 samples (see
Table 4-21).
When the OS_SEL[1:0] bits are set for 6-sample pointer offset, no boundary-checking is
performed.
In HD mode the audio FIFO is a maximum of 10 samples deep. According to SMPTE
299M, audio samples are multiplexed immediately in the next HANC region after the
audio sample occurs.
Table 4-21:Audio Buffer Pointer Offset Settings
OS_SEL[1:0]
00
01
10
Buffer Pointer Offset
26 samples (default)
12 samples
6 samples
Sample Delay
When extracting SD audio, certain conditions can cause the sample delay through the
audio FIFOs to be 1-4 samples different between channels.
If delays through the audio FIFOs must be the same, it is recommended that the FIFO
size gets set to 22 or 16 with OS_SEL[1:0]. Additionally, the audio FIFO must be cleared
when either of the following occurs:
1. Loss of lock. The FIFO should be cleared when the part has relocked.
2. When one of the groups of audio disappears and re-appears. Poll the audio data
packet detected registers ADPG1_DET, ADPG2_DET, ADPG3_DET, and ADPG4_DET
once every frame. If one of the groups currently de-embedded disappears and
re-appears, clear the audio FIFO after the group re-appears.
GS2971A 3Gb/s, HD, SD SDI Receiver
Data Sheet
54311 - 2
September 2012
90 of 152