Cirrus Logic CobraNet Audio Routing Primer - Manual (Page 2)

Components of Routing
Bundles
A Bundle is the basic unit of data for transporting audio over a CobraNet TM network and can contain from
zero to eight audio sub-channels. Sample size, sample rate and transmission latency all have an impact on
processor bandwidth and packet sizes required to process and transmit the audio data. These factors can limit
the number of audio channels that can be processed by a CobraNet
TM interface. The maximum number of
audio sub-channels allowable per bundle will be from 3 to 8 depending on these settings. The maximum
number of bundles possible can also be affected by these settings. Maximum sub-channel count per bundle
will typically be eight but may be less depending on the particular configuration.
An important attribute of the Bundle is the identifying number assigned to it (the Bundle number). The
Bundle number determines both where the data is sent and, to a large extent, how it is sent. When a receiver
on one interface is assigned the same bundle number as that of a transmitter on another interface, the
CobraNet
TM protocol will automatically establish a connection and begin transmitting audio data between the
interfaces.
Bundles can be transmitted using the following modes:
• Unicast (one-to-one)
• Multiple unicast (up to four copies unicast to more than one receiver)
• Multicast (one bundle to an unlimited number of receivers)
• Private (same as unicast or multicast but requiring specification of a MAC address)
Refer to the Programmer’s reference for information on valid bundle numbers and how they affect addressing
modes.
Network Transmitters and Receivers
Transmitters and Receivers are logical entities within the CobraNet TM interface which are closely coupled to
the concept of Bundles. Each transmitter or receiver is capable of sending or receiving one Bundle. The
number of transmitters and receivers within a CobraNet
TM interface is dependant on the particular
implementation and is fixed by the firmware. The user can configure the number of available transmitters or
receivers to be used.
Synchronous Serial Interface
Each CobraNet TM interface contains one or more Synchronous Serial Interfaces, or SSI’s. SSI’s carry
multiplexed audio data into and out of the CobraNet TM interface in time slices and are typically connected to
DACs, ADCs, DSP processors and other digital audio interfaces. See Appendix C for more information on
the SSI.
Audio Routing Channels
Audio routing channels are used to map audio data between a multiplexed SSI time slice and a bundle sub-
channel. CobraNet
TM interfaces contain up to 64 audio routing channels numbered from 1 to 64. Channels 1-
>32 are used for transmitting and channels 33->64 are used for receiving. The actual number of routing
channels available is dependant on the particular CobraNet
TM implementation. Channel 0 is an additional
special case which is, strictly speaking, not a routing channel. Channel 0, when assigned to a transmitter
Bundle, will cause transmission of an empty channel equivalent to silence. Channel 0, when assigned to a
receiver bundle sub-channel, will cause the bundle sub-channel received to be discarded.
For practical purposes, each unique audio routing channel can be thought of as having a fixed association
with a unique SSI time slice. In reality, audio routing channels are assigned to SSI time slices via the
audioMap variable array. Omission of this variable in Figure 1 is intentional. It should not be changed. See
Appendix B for default SSI to Audio Routing channel assignments.
CobraNet TM Audio Routing Primer Rev. 1.2 ©Copyright 2004 Cirrus Logic, Inc
Page 2 of 9