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3.8.5

SAP Input to SAP Output—Processing Flow

TAS3108, TAS3108IA

AUDIO DIGITAL SIGNAL PROCESSORS

SLES152B – OCTOBER 2005 – REVISED NOVEMBER 2007

All SAP data format options other than I2S result in a two-sample delay from input to output, as shown in

Figure 3-7. If I2S formatting is used for both the input SAP and the output SAP, the polarity of LRCLK in

Figure 3-7 must be inverted. However, if I2S format conversions are performed between input and output,

the delay becomes either 1.5 samples or 2.5 samples, depending on the processing clock frequency

selected for the audio DSP core relative to the sample rate of the incoming data.

The I2S format uses the falling edge of LRCLK to begin a sample period, whereas all other formats use

the rising edge of LRCLK to begin a sample period. This means that the input SAP and audio DSP core

operate on sample windows that are 180

° out of phase, with respect to the sample window used by the

output SAP. This phase difference results in the output SAP outputting a new data sample at the midpoint

of the sample period used by the audio DSP core to process the data. If the processing cycle completes

all processing tasks before the midpoint of the processing sample period, the output SAP outputs this

processed data. However, if the processing time extends past the midpoint of the processing sample

period, the output SAP outputs the data processed during the previous processing sample period. In the

former case, the delay from input to output is 1.5 samples. In the latter case, the delay from input to output

is 2.5 samples.

Therefore, delay from input to output can be either 1.5 or 2.5 sample times when data format conversions

are performed that involve the I2S format. However, which delay time is obtained for a particular

application is determinable and fixed for that application, providing care is taken in the selection of

MCLKI/XTALI with respect to the incoming sample clock, LRCLK.

Physical Characteristics

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