Fusion 878A
2.0 Functional Description
PCI Video Decoder
2.18 Digital Audio Packetizer
100600B
Conexant
2-59
2.18.7 Audio Data Formats
provides a summary of audio data formats (signed integer 16/8-bit)
flowing through the audio FIFO. The audio data path is illustrated in
2.18.8 Audio Dropout Detection
When a FIFO overflow occurs due to long bus access latencies, some data will not
be written to the targeted memory buffer. When the DMA resumes, data writing
begins at the address, as if all the skipped data were written. Thus, there would
exist a hole or gap in the memory buffer containing old or stale data. By
initializing the buffer DWORDs to 0x80008000 (0x808080) it is possible to
detect words or bytes of audio not delivered (down to a single sample resolution
level).
Enabling DA_LMT will cause the audio DMA to exclude writing 0x8000
words or 0x80 bytes (mode determined by DA_SBR) to the memory buffer. When
the DAP detects 0x8000, it replaces this code with 0x8001 while in 16-bit mode.
The 0x8000 sample is usually not present since it represents the most negative
value of a 2’s complement 16-bit integer. While in 8-bit mode, 0x80 samples will
be replaced by 0x81.
Table 2-14. Audio Data Formats
Format
F[35:32]
F[31:24]
F[23:16]
F[15:8]
F[7:0]
8-bit Samples
Status
S3[7:0]
S2[7:0]
S1[7:0]
S0[7:0]
16-bit Samples
Status
S1[15:8]
S1[7:0]
S0[15:8]
S0[7:0]
L,R Digital Audio
Status
R[15:8]
R[7:0]
L[15:8]
L[7:0]
Data
Status
D3[7:0]
D2[7:0]
D1[7:0]
D0[7:0]
Figure 2-27. Audio Data Path
879A_031
TV
FM
Mic
Audio
ADC
Decimation
LPF
DAP
35 x 36
FIFO
DMA
PCI Bus
