Hardware Reference
In-Depth Information
What is needed is a heterogeneous multiprocessor containing multiple cores, each
specialized for one particular task. An example DVD player is given in Fig. 8-12.
NTSC/PAL/SECAM
composite video
encoder
Audio
decoder
MPEG video decoder
Disk controller
Control processor
Cache
Memory
Heterogeneous
multiprocessor chip
with six cores
Bus
Figure 8-12.
The logical structure of a simple DVD player contains a heteroge-
neous multiprocessor containing multiple cores for different functions.
The functions of the cores in Fig. 8-12 are all different, with each being care-
fully designed to be extremely good at what it does for the lowest possible price.
For example, DVD video is compressed using a scheme known as
MPEG-2
(after
the
Motion Picture Experts Group
that invented it). It consists of dividing each
frame up into blocks of pixels and doing a complex transformation on each one. A
frame can consist entirely of transformed blocks or it can specify that a certain
block is the same as one found in the previous frame but located at an offset of
(
y
) from its current position except with a couple of pixels changed. Doing
this calculation in software is extremely slow, but it is possible to build an MPEG-2
decoding engine that can do it in hardware quite rapidly. Similarly, audio decoding
and reencoding the composite audio-video signal to conform to one of the world's
television standards can be done better by dedicated hardware processors. These
observations quickly lead to heterogeneous multiprocessor chips containing multi-
ple cores specifically designed for audio-visual applications. However, because the
control processor is a general-purpose programmable CPU, the multiprocessor
chip can also be used in other, similar applications, such as a DVD recorder.
Another device requiring a heterogeneous multiprocessor is the engine inside
an advanced cell phone. Current phones sometimes have still cameras, video cam-
eras, game machines, web browsers, email readers, and digital satellite radio re-
ceivers, using either cell-phone technology (CDMA or GSM, depending on the
country) or wireless Internet (IEEE 802.11, also called WiFi) built in; future ones
may include all of these. As devices take on more and more functionality, with
watches becoming GPS-based maps and eyeglasses becoming radios, the need for
heterogeneous multiprocessors will only increase.
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