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GS1671 HD/SD SDI Integrated Receiver

Data Sheet

53737 - 2

September 2012

73 of 130

4.18.3.3 Audio FIFO Block

The function of the FIFO block is to change the audio data word rate from the ANC rate

multiplexed with the video signal to the 48kHz audio output rate.

The audio FIFO block contains the audio sample buffers; one per audio channel. Each

buffer is 36 audio samples deep. At power up or reset, the read pointer is held at the zero

position until 26 samples have been written into the FIFO (allows for 6 lines per frame

with no audio samples; a maximum of 4 samples per line in SD Mode). See Figure 4-36.

Figure 4-36: Audio Buffer After Initial 26 Sample Write

The position of the write pointer with respect to the read pointer is monitored

continuously. If the write pointer is less than 6 samples ahead of the read pointer (point

A in Figure 4-37), a sample is repeated from the read-side of the FIFO. If the write pointer

is less than 6 samples behind the read pointer (point B in Figure 4-37), a sample is

dropped. This avoids buffer underflow/overflow conditions.

Figure 4-37: Audio Buffer Pointer Boundary Checking

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 4-20).

AudioBuffer

Read

Pointer

Write

Pointer

Address

AudioBuffer

Read

Pointer

Write

Pointer

Write

Pointer

Address

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