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Bits

0:3 A tag (see below)

4:28 PCM encoded sample value

29:31 User bits (parity, etc)

Figure 20:

S/PDIF RX

Word

Structure

Tag Meaning

FRAME_X Sample on channel 0 (Left for stereo)

FRAME_Y Sample on another channel (Right if for stereo)

FRAME_Z Sample on channel 0 (Left), and the ﬁrst sample of a frame; can be used if

the user bits need to be reconstructed.

Figure 21:

S/PDIF RX

Tags

3.11.1 Integration

The S/PDIF receive function communicates with the clockGen component with

passes audio data to the audio driver and handles locking to the S/PDIF clock

source if required (see Clock Recovery).

Ideally the parity of each word/sample received should be checked. This is done

using the built in crc32 function (see xs1.h):

/* Returns 1 for bad parity , else 0 */

static inline int badParity ( u nsigned x)

{

unsigned X = (x > >4) ;

crc32 (X, 0, 1) ;

return X & 1;

}

If bad parity is detected the word/sample is ignored, else the tag is inspected for

channel and the sample stored.

The following code snippet illustrates how the output of the S/PDIF receive compo-

nent could be used:

while (1) {

c_spdif_rx : > data ;

if( badParity ( data )

continue ;

tag = data & 0 xF ;

sample = ( data << 4) & 0 xFFFFFF00 ;

switch ( tag)

{

case FRAME_X :

REV 6.1

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