Handbook for Sound Engineers

Digital Audio Interfacing and Networking 1509

4. Determine if each bundle can be unicast, or if it
   must be multicast.


5. Make sure you don’t have more than four multicast
   bundles in a network. If you need more than four
   multicast bundles:
   
   
   • Consider using multiple switched networks or
     VLANs.
   
   
   • Consider transmitting several unicast bundles
     instead of one multicast bundle.
   
   
   • Use the following rules to see if you can send
     more than four multicast bundles on a given
     network or VLAN:
   
   
   • Carefully map the number of bundles sent to
     each port of the system. The total of multicast
     and unicast Bundles arriving at each switch port
     may not exceed eight.
   
   
   • If a half-duplex device that can only transmit
     two bundles, and is set to transmit using both its
     bundles is part of the network, then you must
     make sure that the network conductor is not
     transmitting a multicast bundle. This may
     require changing the default conductor priority
     of one or more devices in the system to assure
     this condition is met.
   
   
   • Map the bundles carried by every link in the
     system to make sure that the limit of 8 bundles
     each direction on a given fast Ethernet connec-
     tion is not exceeded.
   
   
   
   

39.12.12 CobraCAD®

Fortunately there is an easier way to do steps 5 and 6
above. CobraCAD® can be downloaded for free from
the Cirrus Logic Web site. CobraCAD® is a new soft-
ware tool that provides a simple graphical user interface
for the design and configuration of CobraNet®
networks.
It allows you to draw your proposed CobraNet®
network design using any of the CobraNet® devices on
the market as of when the version you are using was
released. You may also use any of a large selection of
Ethernet switches.
After drawing the physical Ethernet interconnec-
tions, you next draw the bundle connections between
the CobraNet® devices.
Then just press the Design Check button, and
CobraCAD® will perform a design rule check. Designs
that pass this check are extremely likely to work in the
real world. There are still a few things CobraCAD®
can’t check for, so be sure to read the information and
disclaimers in the Help system.

You may also want to check Cirrus Logic’s

CobraNet® Web site at: http://www.cobranet.info/ for

the most recent version.

39.12.13 CobraNet® Hardware

At the heart of the CobraNet® interface, as shown in

Fig. 39-57, is the digital signal processor, or DSP. It

runs the software that together with the hardware

provide all CobraNet® and Ethernet functions. It stores

all the audio and Ethernet information as needed in

stacks in the SRAM, converts the incoming synchro-

nous audio into isochronous packets for transmission

over the network, and converts isochronous packets

from the network back into synchronous audio outputs.

The DSP provides all interface functions to and from

the device in which it is installed, and controls all other

parts of the CobraNet® interface including the sample

clock.

The sample clock is a voltage controlled crystal

oscillator (VCXO), which is under the control of the

DSP. If the CobraNet® interface is serving as the

conductor, the sample clock is fixed in frequency and

serves as the master clock for the network. In all other

interfaces on the network, the sample clock is adjusted

by the DSP so that it locks to the frequency of the

network master clock.

The CobraNet® interface provides its clock signal to

the device it is part of, but can also receive a clock

signal from the device and use that signal as the

network master clock if the interface is the conductor.

The CobraNet® interface can provide up to thirty

two synchronous digital audio signals to the device, and

accept up to thirty two synchronous digital audio signals

from the device for transmission across the network.

The serial port can accept serial data which is then

bridged across the network and appears at all other

CobraNet® devices on the network.

The host interface allows bidirectional communi-

cation and control between the CobraNet® interface

DSP and the processor of the host device in which the

interface is located. Detailed information on the connec-

tions and signals on the CobraNet® interface to the host

are available in the CobraNet® Technical Datasheet

found in pdf form on the Cirrus Logic’s CobraNet®

Web site at: http://www.cobranet.info/.

39.13 Aviom

Aviom uses the Physical Layer of Ethernet. In other

words it is transported over Cat5e cable with RJ-45

connectors. It does not use any other parts of Ethernet,