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The Strengths and Weaknesses of ‘General Purpose’ and ‘Special Purpose’
Consider, for example, the two methods that
could be used to implement a new project.
One is to train the current members of the
team in the new area and have them perform
the work. The other is to hire specialists who
already have field-specific knowledge and
know-how related to the work at hand.
There are limits to the approach of retraining
the current members. Their work load
increases due to having to deal with work
they are not familiar with and the efficiency
with which they will perform the work will
fall short of that of specialists. Yet if we were
to hire new staff every time the work
changed, the hiring costs would spiral out of
hand.
Everything has its strengths and weaknesses.
A similar problem arises in digital signal processing
in audio equipment.
If we use a general-purpose DSP and CPU
to implement decoding processing and sound
effects processing, we can implement a wide
range of functions and handle many formats
simply by changing the software. This is an
important point for today's audio equipment
market, in which the trend towards increasing
multifunctionality is accelerating, and the
numbers of compression schemes and music playback modes are increasing as well.
At the same time, however, this approach has
the demerit that it places a heavy burden on
the general-purpose processor and results in
high power consumption levels.
In contrast, low power can be achieved by
using optimal circuits if we develop special-purpose
circuits. This approach, however, has
the problem that new hardware (circuits)
must be added for each function or data format
and thus it lacks flexibility, and cannot
respond to the needs of the times.
It is dynamic reconfigurable circuit technology,
that is, the VME, that can resolve this
dilemma.
The Concept of Dynamic
Reconfiguration
Although we have talked about reconfiguring
circuits or transforming an LSI, this of course
does not mean that the multiple circuit units
in the LSI are physically moved.
Rather, this technology makes it possible to
transform the LSI into a special-purpose circuit
that is optimal for the desired function
by changing with software the connection
structure and operational settings of the multiple
circuit units provided in advance, that
is, by changing the roles and combinations
of units used.
A single LSI operates, without waste or inefficiency,
in a manner close to a special-purpose
LSI on an instant by instant basis.
This epoch-making technology can achieve
a major reduction in power consumption.
Linkage with the CPU is also
a Key
Sony had to come up with many new ideas
to integrate the VME with a CPU, a USB
interface, and other circuit blocks on the same
chip. For example, to take full advantage of
the characteristics of the VME, the clock lines
and other aspects of the layout had to be analyzed precisely to keep the overall power consumption
to a minimum.
The division of labor between the VME and
the CPU is also an important point. The VME
handles functions that involve heavy processing
and consume power while the CPU
handles lighter control operations. This can
reduce the power consumed by the CPU.
Expanding the Possibilities of
Mobile Equipment
The CXR704060 is a low-power LSI that includes
a VME and is based on Sony’s SoC
(System on a Chip) technology. At the same
time as having a major impact, those characteristics
have resulted in the device being accepted
by the audio market.
The NW-E405 Network Walkman® has attracted
much interest since its release on April
21 this year. While its ability to provide up
to 50 hours* of continuous playback has been
one reason for its popularity, it is its CXR704060 with an on-chip VME that
makes this stamina possible.
The Network Walkman uses software programming
to support not only different audio
compression formats such as ATRAC3,
ATRAC3plus, and MP3, but a wide range of
sound effects as well. Furthermore, the
CXR704060 achieves an LSI power consumption
during audio playback (ATRAC3
playback) of roughly one quarter to one fifth
of that of earlier LSIs.
At the same time as aiming for even further
evolution of the VME, Sony is also working
on concrete business plans for other LSIs that
could include the VME. Keep your eye on
Sony’s VME, which radically increases flexibility
for conceiving of and developing new
mobile products.
*: When using the internal rechargeable battery,
ATRAC3 at 105 kbps, and normal power saving
mode. |
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Vol.42
