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The Death of the DSP
by
Nick Tredennick
In his keynote address at the DSP World conference in San Jose, John Scarisbrick, a vice
president at Texas Instruments, proclaimed this the “era of the DSP.” If that’s so, why does the
title of this serial predict the death of the DSP? Perhaps we’re both correct, but John and I seem to
be at odds on this one, so an explanation is in order. To resolve the dilemma, we’ll need some
tools. I’ll begin with an overview of the embedded systems market. I’ll use a simple taxonomy
I’ve derived to help with the analysis of embedded systems applications. I’ll go from there to a
short description of design methods and what they mean for the applications. With those pieces,
we’ll be ready to analyze the future of the embedded systems market. With the tools and analysis,
I should be able to convince you that the long-term prospect for DSPs doesn’t look good.
The embedded systems market
The embedded systems market, which includes applications for embedded microprocessors,
includes the high-volume consumer applications that drive the electronics industry. Analysis of
the embedded systems market, which is the market for all but two percent of microprocessors,
will tell us where the electronics industry is headed. The embedded systems market consists of
four overlapping segments, defined by their design requirements. Figure 1 illustrates the
dominant-characteristic taxonomy of the embedded systems market.
Figure 1. Embedded systems market segments.
The zero-cost segment, which to a first approximation represents almost all of the embedded
systems market, is the segment for which low cost is the overriding consideration. Most
microprocessors go into consumer appliances (microwave ovens, electric razors, blenders,
toasters, and washing machines) that generally have minimal processing needs. These are
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commodity markets: that means they sell in high volumes (millions of units to tens of millions of
units). These markets are characterized by intense price competition, so substantial effort goes
into reducing production cost. The ideal would be zero cost to implement.
The zero-power segment, which to a first approximation represents a few percent of the
embedded systems market, is the segment for which zero power dissipation represents the ideal.
These applications are consumer items, such as smoke detectors, cellular phones, pagers,
pacemakers, hearing aids, MP3 players, and pocket calculators. Consumers want them to run
forever on a single button-size battery or on weak ambient light. As with all consumer
applications, minimum product cost remains a concern.
The zero-delay segment, which to a first approximation represents a little more than zero percent
of the embedded systems market, is the segment for which zero delay from data in to result out
represents the ideal. These applications are also consumer items, such as high-end printers,
scanners, copiers, and fax machines, for which processing power and throughput are important—
at minimum product cost, of course.
The zero-volume segment, which to more than a first approximation, represents zero percent of
the embedded systems market, is the segment for which the application potential is nearly zero. If
the application volume is going to be very close to zero, then production volumes and profits will
also be close to zero. There must be some other reason to attempt to capture the application. One
motive is public relations. Intel invested considerable money and effort in the design of the
80960MX microprocessor, for which, at the time of implementation, the only known application
was the YF-22 aircraft. When the only prototype of the YF-22 crashed, the application volume
for the ’960MX actually went to zero, but even if the program had been successful, Intel could
not have expected to sell more than a few thousand processors for that application. Intel must
have made the investment in the ’960MX for reasons other than potential application volume and
eventual profit.
Public relations and a leading-edge image motivate support for the zero-volume segment. GM and
Ford’s NASCAR racing teams support the auto industry’s zero-volume segment (for the same
reason Intel once supported the zero-volume microprocessor segment). NASCAR.com serves
more pages to sailors in the U.S. fleet than any other web site. Good public relations has long
term value for other branded products.
The embedded systems market is four segments: zero-cost, zero-power, zero-delay, and zerovolume. Most applications fall within the zero-cost segment, which is by far the largest segment.
Virtually all consumer applications fall within the zero-cost segment. Because consumer markets
are competitive, cost is always a concern for these products. The zero-power and zero-delay
segments overlap substantially with the zero-cost segment. The zero-volume segment overlaps
with the zero-delay segment, but is completely disjoint from the zero-cost segment.
Design methods
Before the microprocessor, engineers solved problems directly. That is, they selected hardware
resources and mapped the algorithm directly into hardware. Anyone who reverse engineered a
circuit could determine the problem it solved. Direct hardware implementation employs fixed
resources and fixed algorithms.
Invention of the computer changed the way engineers solved problems. In the mid-forties, when
computer was invented, hardware was expensive. Computer problem solving employed fixed
resources and dynamic algorithms. The computer could iterate to solve a problem, which
amortized the expensive hardware resources over time for a single problem. Because the
algorithm was entered by a program, the computer could amortize the cost of expensive hardware
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across a range of problems. Before the introduction of the computer, the engineer was responsible
for selecting the hardware resources and for mapping the algorithm into the hardware to solve the
problem. After the introduction of the computer, the engineer programmed algorithms onto the
computer’s fixed resources to solve problems. Problem solving became programming. Reverse
engineering a microprocessor-based circuit might not tell you much about what the circuit does.
(You would have to analyze the programs together with the hardware and not just the hardware.)
Computer
Architecture
Application
Algorithm
Compiler
HLL
Description
Object
Code
Computer
Data
Result
Figure 2. A computer implementation of an application.
As Figure 2 shows, the computer-based solution isn’t direct. The application is translated to an
algorithm that is mapped onto the computer’s fixed resources via a high-level language
description that must be compiled into object code for the microprocessor. Each of these
translations hinders efficiency. The high-level language and its compiler may not be an ideal
match for either the application or the computer. The computer’s instruction set may not be an
ideal match for the application, leading to inefficiencies in code length, execution time, and
power dissipation. The fixed resources provided by the computer may not match the application,
leading to inefficiencies in the algorithm selected to solve the problem. The computer’s fixed
resources may be less than ideal for the application, leading to increased register management in
solving the problem. This leads to inefficiencies in code length and in execution time.
The computer does not solve problems faster than a direct hardware implementation; it solves
problems more affordably. In 1971, Intel introduced the first commercially available
microprocessor. The integrated circuit digital signal processor (DSP) followed a few years later.
Introduction of the microprocessor and DSP brought programming as a problem-solving method
to the world of embedded systems. In embedded systems the microprocessor and DSP don’t solve
problems faster than a direct hardware implementation; they, like the computer, solve problems
more affordably. Given that the microprocessor- or DSP-based solution can meet the minimal
performance requirements of most embedded applications, what matters most in embedded
systems is cost. The microprocessor and DSP, by virtue of their universal application to a range of
problems, achieve the high volumes necessary to decrease manufacturing cost and to amortize
development cost. High volume production lowered the cost of microprocessors and DSPs so that
they eventually displaced TTL as the means of choice for implementing embedded applications.
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Because the microprocessor and its cousin the DSP are general-purpose devices, they cover a
broad range of applications. The cost of covering a broad range of applications is that the
microprocessor or the DSP is not likely to be a perfect solution for any of them. Since the vast
majority of embedded systems have access to infinite power, at least relative to the needs of the
microprocessor or DSP, the power-efficiency of the design and of the processors themselves has
not been an area of emphasis. It didn’t matter, for example, whether the microprocessor
controlling a 1500-watt hair dryer or microwave oven dissipated one or two watts.
Since cost is generally the primary concern in an embedded system, improving the efficiency of
the designer carries high value. Raising the efficiency of the designer shortens time to market and
reduces development cost. TTL displaced discrete components in designs because it increased the
designer’s efficiency. The engineer designed with macro functions rather than with low-level
devices. This sped the design process (saving development cost and getting products to market
sooner). The microprocessor and the DSP further improved the designer’s efficiency by again
raising the level of abstraction, this time to programming an algorithm into fixed resources
provided by the microprocessor or the DSP.
Dynamic logic and the DSP
The taxonomy of embedded applications is important because it says where the electronics
industry is headed. Continued improvement in semiconductor fabrication, continued proliferation
of cellular telephones, and growing popularity of handheld devices (digital cameras, GPS
receivers, PDA s, etc.) drive more computing into portable devices. Because they are consumer
devices, they fall into the zero-cost segment. Because they have high computing requirements,
they fall into the zero-delay segment. Because they are portable devices, they fall into the zeropower segment. We all want cheap, highly capable devices that give us instant answers and that
work on weak ambient light. The overlap of the zero-cost, zero-delay, and zero-power segments
is the leading-edge wedge. Figure 3 illustrates the le ading-edge wedge.
Figure 3. The leading-edge wedge is the overlap of zero cost, zero power, and zero
delay.
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As Figure 1 and Figure 3 show, the leading-edge wedge is a tiny percent of the embedded
systems market, but it is growing rapidly and it can have better margins than most embedded
applications. The leading-edge wedge is growing rapidly as the popularity of mobile consumer
devices rises. Applications in the leading-edge wedge will drive the direction of the electronics
industry and they will take the designers with them. The leading-edge wedge is the future for
mobile embedded systems applications. Tomorrow’s engineers will have to design applications to
meet the requirements of this wedge.
The programmable logic device (PLD) is conceptually a two-layer device. One layer is logic and
interconnect (wires) and the second layer is memory. Values in the memory connect wires to
logic cells to build complex logic circuits.
Figure 4. A programmable logic device is interconnect and logic plus memory for
configuration.
An embedded system application can be implemented more directly using programmable logic
than using a microprocessor or DSP. The algorithm representing the application can be compiled
directly into gates implementing the design. If the application must implement an assortment of
algorithms, as in the multi-protocol cellular phone, for example, the implementation of a
particular protocol can be “paged” into the programmable logic on demand. Paging functions into
programmable logic can be efficient. Idle functions are not paged into the programmable logic
and do not use power.
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Application
Algorithm
Compiler
Processor
Data
Result
Figure 5. A programmable logic implementation.
Compare Figure 5 with Figure 2 to see how much more directly programmable logic implements
an application. The compiler translates the algorithm into resources that execute the application
directly. Processing flexibility is one advantage programmable logic implementations have over
microprocessor- or DSP-based implementations. Programmable logic resources can be configured
to implement parallel functions or a function of any (reasonable) number of bits. Unlike the
microprocessor or DSP, which implement fixed resources and rely on dynamic algorithms,
dynamic logic implements dynamic algorithms and dynamic resources.
Commercially available PLDs, though they are capable of implementing dynamic logic, aren’t
ideal for embedded applications. Historically, PLDs have been used for prototyping circuits. That
is, engineers designed a circuit and built a prototype using PLDs. If the circuit performed its
functions properly the engineers submitted the design files to create an application-specific
integrated circuit (ASIC). PLDs have historically been expensive, slow to reconfigure, didn’t
allow partial reconfiguration or reconfiguration during operation, and have had poor performance
and poor transistor efficiency relative to an ASIC implementing the same function. For these
reasons, PLDs are not a good choice for dynamic logic circuits. Leading PLD manufacturers such
as Altera and Xilinx have been too busy scrambling to supply components to meet demand in
rapidly growing markets for high-margin prototyping and for tethered network communications
devices and have therefore not designed their components to meet the needs of dynamic logic
applications. There is no incentive for manufacturers to design PLDs to meet the requirements of
dynamic logic applications as there is currently little demand.
QuickSilver Technology
Jamie Cummins and John Watson left Xilinx, a leading PLD manufacturer, to start QuickSilver
Technology, Inc. Before I describe how QuickSilver might change the world, I have to tell you a
little about what QuickSilver is doing. And I have to tell you a little about how the embedded
systems market looks and where I think it is headed.
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QuickSilver is building a next-generation cellular phone using dynamic logic (QuickSilver’s term
for this is Adaptable Computing Machine). Logic for each of the phone’s protocols and functions
can be “paged” into the chip’s programmable logic, eliminating the need for a digital signal
processor, ASICs, and possibly even the usual microprocessor. Functions that are not paged into
the chip’s gates do not use power. Efficiency improves because the implementation is more direct
(compare Figure 5 with Figure 2) for each function than it is in a DSP-based implementation. The
DSP-based implementation runs a variety of functions on a fixed set of resources, giving up
efficiency for the sake of simplifying the programming and the hardware resources. The dynamic
logic solution gives up efficiency in “paging” functions into the programmable logic.
QuickSilver’s bet is that paging the logic into the chip will cost less power than having logic that
is always resident but mostly idle.
QuickSilver will circumvent the inefficiencies of PLDs designed for the commercial prototyping
market by designing its own devices to suit just the anticipated range of applications.
QuickSilver’s Adaptable Computing Machine (ACM ) will still be a PLD, but it will be designed
for rapid partial reconfiguration to accommodate “paging” of its functions. QuickSilver’s ACM
will allow background reconfiguration while the device is operating. It may even cache high-use
logic functions for more efficient paging (though this would cost valuable power). In addition,
QuickSilver’s ACM , since it is not being designed for general-purpose prototyping, can be
designed with much less overhead than a commodity PLD, which typically has about twenty
transistors of overhead for each transistor in the implemented function. In addition, the peripheral
circuitry can be designed to suit a single system rather than being the general-purpose, universally
configurable I/O pad ring required by PLDs for prototyping applications.
One application for QuickSilver’s ACM is a mobile device (see Figure 6) that could be a multimode, multi-protocol cellular phone. This phone might allow roaming among protocols such as
AMPS, CDMA, TDMA, and GSM and even among frequency bands. Since it is “adaptable,” it
could be updated to the third generation standards even as they evolve. In addition to the cellular
phone functions, the device could also accommodate a variety of other functions such as calendar,
calculator, email, GPS, and MP3. It might ship with a standard set of functions that could be
“paged” from ROM and a bank of flash memory to accommodate changes and installation of new
functions. These changes and new functions might be loaded over the air interface, keeping the
device functional and current in the field much longer than devices based on ASICs and ROM
programs.
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qst solution
What if silicon can adapt
on-the-fly to become the
right engine for many things?
Adaptable Computing Machine
Versus...
...
...
QuickSilver Technology Inc.
Figure 6. QuickSilver’s (QST) illustration of an Adaptable Computing Machine that
implements flexible applications in a portable device.
In leading-edge wedge applications, such as QuickSilver’s example mobile device, the embedded
system must meet the conflicting demands of compute-intensive algorithms and of long battery
life. The processing requirements of these applications can be demanding across a range of
subtasks. The cellular telephone, for example, must do call setup, call teardown, encoding,
decoding, and a variety of protocol processing subtasks. These applications typically require
several application-specific integrated circuits (ASICs), a digital signal processor (DSP ), and a
microprocessor. The world has not converged on a single cellular standard and is not likely to any
time soon, so there is demand for multi-protocol cellular phones. A separate ASIC typically
supports each protocol. Increasing popularity of email and the demand for wireless connection to
the Internet are driving demand for these functions into the cellular phone as well. Each of these
added functions adds processing complexity and makes extending battery life more difficult. The
programmable logic device (PLD ) may offer a way out of this difficult situation. QuickSilver’s
Adaptable Computing Machine (ACM ) uses dynamic logic. That is, ACM s implement dynamic
algorithms and dynamic resources.
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work / power tradeoff
uP
A
B
A
B
D
E
DSP
C= A+B
D
E
F= D+E
G= C+F
G =A+B+D+E
A
B
ACM
G =A+B+D+E
D
E
GOOD
1
Changing the Computation
Model Improves Performance
and Power Consumption
100
1000 BAD
Relative Clock Cycles / function
QuickSilver Technology Inc.
Figure 7. QuickSilver’s illustration of computing differences among
microprocessors, DSPs, and its Adaptable Computing Machine (ACM).
QuickSilver’s ACM can be significantly more efficient than a DSP-based implementation of the
same functions. Figure 7 illustrates one aspect of increased efficiency for dynamic logic
implementations. Resources on the chip can be allocated to the limit of availability for parallel
computation, since the resources are not dedicated to particular functions as they would be in a
microprocessor, DSP, or an application-specific integrated circuit (ASIC). A large fraction of the
fixed resources in a microprocessor or DSP may be idle at any particular time. DSPs generally
work on data in multiples of a byte. Dynamic logic implementations can work on any data width
(the width can even vary with time to suit the needs of the problem).
As semiconductor process improves, DSPs and microprocessors are built with ever more fixed
resources and at ever higher clock speeds, so they are capable of tackling ever more complicated
functions. But, while adding resources and increasing the clock rate improve computational
capability, they don’t improve the computational efficiency of these processors. Each of the
functions “paged” into a dynamic logic implementation makes efficient use of the resources it
needs and is then overwritten as the next function is “paged” into the chip. Computational
efficiency is high, so power dissipation is low. QuickSilver believes that by using a dynamic logic
implementation it can lower power dissipation to be a half to a tenth of a comparable DSP-based
implementation while at the same time improving performance by a factor of ten to 100.
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Dynamic logic will displace the DSP
For over fifty years, the computer has helped engineers solve problems that did not have
affordable alternative solutions. The computer was invented when hardware was expensive.
Engineers learned to implement applications by programming the computer and letting it iterate
to solve the problem. This amortized the expensive hardware resources over time to solve the
problem affordably. It raised the level of abstraction, which made the designers more efficient but
made the designs less efficient.
This computer-based problem-solving method transitioned into the embedded systems market
with the introduction of the microprocessor. The microprocessor displaced logic -macro-functionbased solutions in embedded systems for several reasons:
?? It had adequate performance. (Performance-critical applications still get direct hardware
solutions.)
?? It raised the efficiency of the designer. The designer mapped the application onto a fixed set
of hardware resources via a program. The designer has been the critical resource, so
enormous effort has gone into raising the designer’s efficiency (by standardizing components
and programming languages and by raising the level of abstraction).
?? It achieved high unit volumes and, therefore, low cost by using a few standard components
(memory, microprocessor, DSP, and peripherals) to build a wide range of applications.
?? It applied the engineer’s knowledge of computer-based techniques in solving embedded
systems problems.
DSPs are displacing the microprocessor in compute-intensive embedded applications because
their data-flow organization has higher computational throughput than the microprocessor. But
the microprocessor and the DSP have inherited low design efficiency from the computer. Low
cost and adequate performance have been the hallmarks of embedded systems design for a long
time. Power dissipation has not been the primary concern for the vast majority of embedded
applications that are tethered to a wall socket with access to unlimited power. Applications in the
leading-edge wedge are changing that. As the world goes mobile, computational requirements are
increasing at the same time consumers will be demanding longer battery life from their mobile
devices. Since these mobile devices are consumer items, cost will be a primary concern as well.
The leading-edge wedge is the overlap of the zero-cost, zero-power, and zero-delay segments of
the embedded systems market.
High growth in the leading-edge wedge is the foothold for dynamic logic designs. From there
they will proliferate to the rest of the embedded systems segments. It is the beginning of the long
downhill for the microprocessor and for the DSP. The DSP’s demise will be a long time coming,
however, for two fundamental reasons.
First, the huge zero-cost and zero-delay segments of the embedded systems market outside the
leading-edge wedge will continue to grow. Demand for DSPs and microprocessors will continue
to grow with these segments for some time. Second, our universities have graduated generations
of designers ill-equipped to implement dynamic logic designs. Engineers are trained in
microprocessor- and DSP-based design methods because there has historically been no demand
for dynamic logic design skills. Applications in the embedded systems segments cannot transition
to dynamic logic implementations until there is a significant base of engineers capable of
applying the new design methods. Fortunately, the process can begin with a few design teams
implementing high volume applications. Once companies like QuickSilver prove the worth of
dynamic logic designs, it may spell the death of the DSP.
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