2.0 Functional Description
Fusion 878A
2.18 Digital Audio Packetizer
PCI Video Decoder
2-54
Conexant
100600B
2.18 Digital Audio Packetizer
The Digital Audio Packetizer (DAP) block can packetize data input on ASCLK,
ALRCK, and ADATA in two additional modes besides normal I
2
S mode. It can
also packetize asynchronous parallel data from the GPIO pins (Asychronous Data
Parallel Port). This mode is described in the Electrical Interfaces Asychronous
Data Parallel mode section.
displays the DAP programming map.
2.18.1 Audio FIFO Memory and Status Codes
The audio FIFO is identical to the video 36 × 35 FIFO memory block. The 36 bits
allow for two 16-bit samples (or four 8-bit samples) and a 4-bit status nibble. The
planar mode FM3 code and the VRE code are not generated from the audio
packetizer. The SOL/EOL (1-4) codes bound the finite size audio packets
(number of bytes indicated by ALP_LEN). The size of the data byte buffers may
typically be set to the system memory page sizes. The FM1 and VRO codes
bound a finite number of packets. These delimiter codes are useful for providing
data delivery checks, RISC program loop checks, and synchronization. The PXV
code is used for all valid audio samples between the packetizing codes SOL/EOL.
Both the input and output sides of the FIFO run off the PCI clock.
2.18.2 PCI Bus Latency Tolerance for Audio Buffer
The latency-effective size of the audio FIFO is essentially 32 DWORDs or 64
samples of 16-bit audio. This allows for a maximum PCI bus latency of 286 µs at
224 kHz (381 µs at 149 kHz) sample rate before overflow will occur. This latency
drops to 143 µs when in 8-bit mode, because the rate is 4X and the number of bits
is half. The digital audio input tolerates a maximum latency of 667 µs at 48 kHz
16-bit L,R or 122 µs at 1 MBps data before FIFO overflow.
Table 2-13. Digital Audio Packetizer Programming Map
Audio Control
Registers
I
2
S Mode
Asynchronous Data
Parallel Port
Data Packet Mode
High Speed Serial
Interface
(1)
DA_APP
0
1
0
1
DA_IOM[0]
1
0
1
1
DA_DPM
0
0
1
See
NOTE(S):
(1)
Set DA_SBR to 1 for High Speed Serial Interface Mode.