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ESE Magazine Jan/Feb 06
18
MOST – Intelligent network
interface controllers
Henry Muyshondt, SMSC
The de-facto standard for automotive multimedia now has intelligent interfaces.
MOST, or Media Oriented Systems
Transport, is the de-facto standard for
high-speed multimedia networking in
automobiles, with 35 car models
deploying the technology, using millions of MOST
devices. Several carmakers are also incorporating
the technology into their complete line-ups.
MOST is moving into mid-range car platforms and
may then proliferate into low-end car models.
In the late 1970’s, many automobiles, even
high-end cars, barely used a separate amplifier
and radio. Over the years, audio products, such
as cassette players and CD players, were added.
With more devices in a car needing to interact
with each other the number of connections rose
exponentially, making it necessary to network
the components. This is the need for MOST.
All digital
As the majority of data (music, Video CDs, DVDs,
etc.) is stored in digital format, MOST is an alldigital
system with analog signals only right at
the user interface (speakers and video display).
When a system level approach is taken to implement
a MOST system, significant cost savings are
achieved as duplicated components are eliminated
and functions are integrated into single chips.
MOST specifies not just the physical interconnection
between devices on the network, but
the software layers needed to build up and take
down connections and the APIs needed to control
standard functions, like CD-players, amplifiers,
tuners, etc. In the first generation of MOST,
a Network Interface Controller (NIC) provided
the physical connection to the network, while
NetServices - all the network management software
ran on an External Host Controller (EHC).
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Figure 1: NIC vs. INIC Architectures
The EHC could be any of a variety of microcontrollers
and DSP devices on the market. The NIC
was programmed through a register wall and
the integrity of the network was totally dependent
on the EHC implementation of the
NetServices software and APIs. Early implementations
showed that some of the real-time
responses needed by the low-level network
interfaces were sometimes not met if the EHC
was busy working on other tasks.
MOST NICs are now Intelligent (INICs) and
on the market. With these, the network comes
up as a standalone entity, independent of the
applications that reside on the EHC. INICs take
all the lessons learned during early implementations
and ensure that all the real-time requirements
of network communications are taken
care of without external intervention.
Two Layers
The NetServices software is divided into two
layers. Layer 1 (the Basic Layer) includes the
low level mechanisms needed to initialize
MOST devices and to ensure the proper startup
behavior of the network. This layer includes
functions with real-time response requirements
for the network to function properly.
Layer 2 (Application Socket) includes
required MOST functions and services to support
functional addressing so applications don’t
need to know the physical addresses of other
devices on the MOST network. The functions
included in layer 2 typically do not have hard
real-time requirements.
Figure 1 shows how INIC implements some
of the functions of the old NIC-based approach.
The INIC architecture includes a microcontroller
to implement the functions in NetServices Layer
1 and also the required MOST function block
NetBlock that formerly resided in Layer 2. The
NIC Engine is similar to the old external NIC and
performs the actual formatting of data for transmission
over the physical interconnection.
Message based
Another characteristic of the INIC architecture is
that it uses a message-based interface rather
than a register wall typical in NIC designs. This
interface simplifies the number of commands
that application programmers need to implement
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Figure 2: INIC Architecture Framework
and abstracts things like network speed and
physical layer (e.g. various kinds of optical or
electrical connections) from the application. This
significantly reduces the design-in and verification
efforts, as the network itself becomes a
standalone entity. Specific functions on each
device on the network register themselves as the
device is ready and each device can take its time
initializing itself and its operating system, if there
is one, as well as other peripherals attached to it
without having any effect on the network.
The message-based architecture is implemented
in SMSC’s line of INIC products and will
be used in all future generations of MOST INICs.
This architecture has the advantage that applications
will need few, if any, changes to use
higher speed network implementations or new
physical layers that are introduced over time.
Figure 2 shows a framework for INIC implementations.
oPhy and ePhy represent optical and
electrical physical layers, respectively.
Current MOST systems use Plastic Optical
Fiber (POF) driven with LEDs. Other optical transmission
media such as Polymer Clad Silica (PCS)
and VCSELs (Vertical Cavity Single Emission
Lasers) are also being considered. In addition, a
specification for an electrical physical layer has
been developed by the MOST Cooperation.
The INIC API removes any dependencies on
network speed and physical layer from the applications
that use INIC.
The MOST Cooperation is a not-for-profit
consortium of automakers, suppliers, and related
companies that support the proliferation of
the MOST protocol.
www.smsc.com
www.mostcooperation.com