Crystal CS4281, Programming Manual

Page: 19 / 231

CS4281 Programming Manual
DS308PRM1 19
Confidential Draft 3/7/00
Figure 5 illustrates an 8-channel application where
a primary Codec supports the first four channel and
the secondary codec supports the second 8 chan-
nels. A stream on the CS4281 supports up to two
channels so all four streams are utilized when eight
channel out is active. Therefore, since the CS4281
only supports four simultaneous streams, the stereo
audio in from either codec could not be used while
the eight channel out is active. If only six-channel
out is desired, the fourth stream would be available
for stereo audio recording.
2.1.1 Surround Sound 5.1 Play
No special modes exist to support 5.1 channel sur-
round sound. Surround sound is supported on the
CS4281 in one of two methods. The first is using an
S/PDIF renderer to take the stereo compressed 5.1
channel data and, using one stream, send it through
the CS4281 to a CS4298/97A/99 that supports an
S/PDIF output. The second method is using a filter
on the host to decompress the 5.1 streams into 6
channels of PCM data. Then an Audio Surround
Sound renderer maps the six channels into three
stereo streams for the CS4281. If one of the streams
is left/right PCM data, then the fourth CS4281
stream may be used for system sounds or host
wavetable support. Since de-compressed surround
sound uses three of the four streams supported by
the CS4281, simultaneous host modem is not via-
ble. The six-channel out is supported by configur-
ing a CS4297A as the primary Codec and a CS4294
as the secondary codec. The CS4297A supports
two-channel in and out while the CS4294 can sup-
port the additional 4 channels out.
CPU
North
Bridge
Host
Memory
South
Bridge
CS4281
PCI Audio Interface
AC Link
CS4294
4 Channel
Audio Out
Audio In
PCI Bus
CS4294
4 Channel
Audio Out
Audio In
ASDIN2
Figure 5. Dual-Codec 8-Channel Audio Out Diagram
D
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ft