Digital Signal Processing Reference
In-Depth Information
(2) the system performance or power consumption requirements cannot be achieved
by general purpose processors, (3) the volume is high or the design cost is not a
sensitive parameter, and (4) it is possible to use the ASIP for multiple products.
1.2
The Difference Between ASIP and General CPU
Designers of general-purpose processors think of both the maximum performance
and maximum flexibility. The instruction set must be general enough to support
general applications. The compiler should offer compilation for all programs and to
adapt all programmers' coding behaviors.
ASIP designers have to think about applications and cost first. Usually the
primary challenges for ASIP designers are the silicon cost and power consumption.
Based on the carefully specified function coverage, the goal of an ASIP design is to
reach the highest performance over silicon cost, the highest performance over power
consumption, and the highest performance over the design cost. The requirement on
flexibility should be sufficient instead of ultimate. The performance is application
specific instead of the highest one. To minimize the silicon cost, a design of an ASIP
aims usually to a custom performance requirement instead of an ultimate possible
high performance.
Programs running in an ASIP might be relatively short, simple, with ultra high
coding efficiency, requirements on tool qualities such as the quality of code compiler
could be application specific. For example, for radio baseband, the requirement on
compiler may not really be mandatory.
The main difference between a general-purpose processor and an ASIP DSP is
the application domain. A general-purpose processor is not designed for a specific
application class so that it should be optimized based on the performance of the
“Application Mix”. The application mix has been formalized and specified using
general benchmarks such as SPEC (standard performance evaluation corporation).
The application domain of an ASIP is usually limited to a class of specific
applications, for example video/audio decoding, or digital radio baseband. The
design focus of an ASIP is on specific performance and specific flexibility with low
cost for solving problems in a specific domain. A general-purpose microprocessor
aims for the maximum average performance instead of specific performance.
Except for memories, there were two major families of integrated digital
semiconductor components, microprocessors and ASIC. Microprocessors take the
role of flexible computing of all programs running in desktops or laptops. An
ASIC supplies application specific functionality, and its functional coverage and
performance are fixed during the hardware design time, for higher performance,
lower silicon area, and lower power consumption. In 1980s to 1990s, ASIC played
dominant roles in communications and consumer electronics products, for example,
the radio baseband in mobile phones was based on ASIC.
To get high performance and low power consumption at the same time, embedded
system designers usually use ARM processors attached with non-programmable
