2.0 Functional Description
Fusion 878A
2.18 Digital Audio Packetizer
PCI Video Decoder
2-58
Conexant
100600B
There can be any number of ASCLKs
≥
16 (usually 16–32 between ALRCK
edges. Thus there may be extra ASCLKs versus collected data bits. There is no
requirement for ASCLK (or ALRCK or ADATA)) to be continuous. A specified
edge of ASCLK is used to sample the other two signals. Each 16-bit sample is
sampled a specified number of ASCLK edges from the edge of ALRCK, which
serves as a word sync.
The Number of Bytes/AudioLine ALP_LEN should be DWORD aligned so a
whole number of L, R sample pairs can be delivered to memory. The start of
audio L, R data capture is asynchronous and is enabled with ACAP_EN. The end
of data capture is synchronized to the VRO code DWORD after ACAP_EN is
disabled.
2.18.6 Data Packet Mode
The serial data on ADATA is again sampled with a programmable ASCLK edge.
Data is collected in bytes (shift-register bit order programmable via DA_MLB).
There are no extra ASCLKs between bytes, but there can be extra ASCLKs
between packets (frames of data bytes). The maximum data rate allowed is 1
MBps or 8 MHz for ASCLK. There is no requirement for the interface signals to
be continuous. The signal ALRCK is used for byte alignment and packet framing.
DA_LRD will be used again to delay sampling of the shift-register to output
packet data bytes (DA_LRD ASCLKs after the leading edge of ALRCK indicates
the first bit of the first byte. Successive bytes are transferred every 8 ASCLKs).
DA_LRI will be used to indicate the edge (0 = rising, 1 = falling) of ALRCK to
use for synchronization.
The Number of Bytes/AudioLine ALP_LEN used here indicates the number
of bytes to collect/count per ALRCK sync/framing signal. There can be extra
ASCLKs or data following this count which will be ignored. The FIFO will only
be sent data that belongs to the packet as specified by ALP_LEN bytes from the
start of each ALRCK frame sync. The start of data capture is enabled via
ACAP_EN and then synchronized to the start of a packet. Thus, the byte
synchronized to ALRCK will be the first data byte in the audio line buffer. The
end of data capture is synchronized to the VRO code DWORD after ACAP_EN is
disabled.
illustrates the data packet mode signals.
Figure 2-26. Data Packet Mode Timing
Byte 0
Byte 1
Byte 2
ASCLK
ADATA
ALRCK
LSB
. . .
MSB LSB
. . .
MSB LSB
. . .
MSB
879A_030