Cirrus Logic CobraNet User Manual

Page 24

DS651PM25

CobraNet Programmer’s Reference
Audio Paths

Sample rate is selected by the

modeRateControl variable. modeRateControl selects both

sample rate and audio latency. 96 kHz sample rate and low-latency modes can be used
together.

rxSubFormat indicates the type and status of audio date being received. The LS bit of this
variable indicates whether data in the sub channel is being decoded. A value of

indicates inability of the interface to decode the received data. An interface operating at
48 kHz cannot decode 96 kHz audio. An interface operating at 96 kHz cannot decode
48 kHz audio.

Processing 96 kHz audio requires twice the bandwidth. At 5-1/3 ms latency, all of the data
is transmitted in one packet and thus the number of channels that can be transferred per
bundle may be reduced. Lower latency modes can support more channels at 96 kHz, as
the data is distributed across 4 packets at 1-1/3 mS and 2 packets at 2-2/3 ms latency.
See

Table 5., "Bundle Capacity Limits as a Function of Ethernet Packet Size"

for more

detail on this topic.

When operating in 96 kHz mode, the Master Clock remains at the standard 24.576 MHz.
However, in 96 kHz mode, the Sample Clock Output (FS1) will change to support a
96 kHz signal. If a sample clock cascade and/or reference clock input is supplied, this
signal may be either 48 kHz or 96 kHz in 96 kHz mode but must be 48 kHz in 48 kHz
mode.

Table 7. Bit Clock Rates

Synchronous Serial Port Operating Mode

48 kHz SCK Rate

96 kHz SCK Rate

64Fs (2 channels x 4 interfaces)

3.072 MHz

6.144 MHz

128Fs (4 channels x 4 interfaces)

6.144 MHz

12.288 MHz

256Fs (8 channels x 4 interfaces)

12.288 MHz

24.576 MHz