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Ancillary Data

Quadro SDI Output PG-03776-001_v06 | 34

6.4.1 SMPTE 272M – Standard Definition Audio

In the case of standard definition audio data, SMPTE 272M places up to 20-bits of audio

data along with the block sync (Z), validity (V), user (U), channel (C), and parity (P) bits

into a 32-bit AES subframe. The API requires that the 20-bit audio data and associated

bits also be packed into 32-bits as illustrated Code Listing 32.

Code Listing 32: Formatting SMPTE 272M Audio Data

// SD Audio should be split across 3 ANC words like so:

// X:

// b9 - !b8 (Computed by HW)

// b8 (b8) - aud 5

// b7 (b7) - aud 4

// b6 (b6) - aud 3

// b5 (b5) - aud 2

// b4 (b4) - aud 1

// b3 (b3) - aud 0 (LSB)

// b2 (b2) - ch1 00 = channel 1, 01 = channel 2,

// b1 (b1) - ch0 10 = channel 3, 11 = channel 4

// b0 (b0) - Z

// X+1:

// b9 - !b8 (Computed by FPGA)

// b8 (b17) - aud 14

// b7 (b16) - aud 13

// b6 (b15) - aud 12

// b5 (b14) - aud 11

// b4 (b13) - aud 10

// b3 (b12) - aud 9

// b2 (b11) - aud 8

// b1 (b10) - aud 7

// b0 (b9) - aud 6

// X+2:

// b9 - !b8 (Computed by FPGA)

// b8 (b26) - P - Parity for bits 0-25 of sample.

// b7 (b25) - C - Channel status bit.

// b6 (b24) - U - User bit.

// b5 (b23) - V - Sample validity bit.

// b4 (b22) - aud 19 (MSB)

// b3 (b21) - aud 18

// b2 (b20) - aud 17

// b1 (b19) - aud 16

// b0 (b18) - aud 15

// ^

// `- bit order in 'sample'

// XXX Since we use a 16 bit audio source here

// (input is NvU16), move the 16 bits into

// the upper part of the audio data's 20 bits.

1 2 ... 34 35 36 37 38 39 40 41 42 43 44 ... 146 147

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