GS3471 datasheet(85/179 Pages) SEMTECH

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GS3471

Final Data Sheet Rev.4

PDS-060498

September 2017

85 of 179

Semtech

www.semtech.com

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 4-51), 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 4-51), a sample is

dropped. This avoids buffer underflow/overflow conditions.

Figure 4-51: 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 4-21).

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 ST

299, 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]

Buffer Pointer Offset

FIFO Size

00b

26 samples (default)

01b

12 samples

10b

6 samples

Audio Buffer

Read

Pointer

Write

Pointer

Write

Pointer

Address

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