ETC ASICRCFWP_D

Freescale Semiconductor
White Paper
ASICRCFWP
Rev. 1, 11/2004
ASIC Versus Reconfigurable Compute
Fabric (RCF) Solutions
By Roman Robles
Design managers often accept application-specific integrated
circuit (ASIC)-based solutions as their least expensive option in
developing telephony infrastructure solutions, including
modems. For early-generation wireless base stations, the
demands of code division multiple access (CDMA) air
interfaces and the limitations of programmable digital signal
processors (DSPs) made ASICs a comfortable solution.
However, there may be a price to pay for this comfort. This
paper explores the total cost of ASIC ownership and challenges
the conclusion that ASICs are always the least expensive
choice. It enumerates the benefits of Freescale’s Reconfigurable
Compute Fabric (RCF) technology, which can greatly reduce
engineering development time and project costs while yielding
a longer lasting revenue stream.
© Freescale Semiconductor, Inc., 2004. All rights reserved.
CONTENTS
1
1.1
1.2
1.3
1.4
2
2.1
2.2
2.3
3
The ASIC-Based Solution .......................................2
ASIC Design Flow .................................................. 2
Total Cost of ASIC-Based Design .......................... 4
Amortization of ASIC Development Costs ............5
Cost of Being Late to Market ..................................5
Freescale Solution: Reconfigurable
Compute Fabric .......................................................6
Accelerated Development Methodology ................6
Impact of RCF Methodology on Development Cost 7
Benefits of RCF Methodology ................................7
Conclusion ..............................................................8
The ASIC-Based Solution
1
The ASIC-Based Solution
This section considers the ASIC-based baseband solution for the 3G infrastructure market by taking a look at the
phases in the design flow, estimating the total cost of these development phases, and then considering these costs in
the context of the cost of the ASIC itself and incremental costs of any re-spin of the device.
1.1 ASIC Design Flow
When the cost of an ASIC-based solution is considered, the base of reference is usually the direct silicon cost in
dollars per mm2. In consumer market applications in which the total development cost can be amortized across
very large volumes, this approximation is generally useful. In contrast, infrastructure markets, which are
characterized by low-to-modest volumes and demand greater longevity of product (that is, less churn) amid a
landscape of ever-changing standards, can present a radically different business situation. First, let us explore an
arguably representative case for the development of a large ASIC (~4 to 6 million gates) in an advanced process
(0.13µ to 90 nm). Figure 1 shows a simplified depiction of the steps required to deliver an ASIC-based modem
subsystem. This is the design flow referenced in this paper. The following sections describe the tasks in this flow
and consider the general resources and time frames required to complete these tasks.
Requirements
Definition
System
Design
Logic
Design
Design
Verify
Mask
Generation
Board
Design
Silicon
Fab
Silicon
Verify
Board
Assembly/
Test
Software
Integration/
Test
Ship
Prototype
Board
Fab
Figure 1. Typical ASIC Design Flow
1.1.1 Requirements Definition
A product life cycle begins with a marketing and/or engineering proposal for the product concept. Ideally, a
product proposal gets the benefit of marketing, engineering, and customer inputs during the process of reviewing,
revising, and refining the target behavior and performance of the product. Assuming that these teams have
previous experience in this market and/or with products of related applications, this task can be completed in a
couple of months, though such an aggressive schedule is not typical.
1.1.2 Systems Design: Developing the Modem Architecture
Once the concept is documented and any necessary marketing analyses have warranted that further effort is
justified, systems engineers and systems architects are assigned the task of describing the solution in detail. They
evaluate the trade-offs between different approaches, analyze competing algorithmic options, and survey the
multiple choices in hardware/software partitioning. It may be necessary to develop new algorithms or search for
innovative implementations of existing ones. This stage of development may require significant investment in
research, and the level of resources required to complete this effort varies greatly.
1.1.3 Logic Design
During the logic design phase, the block diagrams and algorithms are converted into source code in a hardware
definition language. This phase consumes much time and many resources. There may be some iteration between
this step and the previous two development steps. Portions of this phase and the verification phase can overlap.
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
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The ASIC-Based Solution
1.1.4 Design Verification
This critical phase of development is frequently underestimated. This phase has been estimated to require more
than twice the effort of the design phase, but added head count can mitigate some of the schedule impact. The
severe cost of re-spin dictates thoroughness of verification. Some of the design verification task can overlap with
logic design, but a significant portion of this task remains after the design is complete.
1.1.5 Mask Generation
Although mask generation is a well-defined and relatively brief task, it is a milestone that very clearly delineates
the end of the design effort and the beginning of the silicon fabrication. Today’s leading edge process technologies
(for example, 0.13µ or 90 nm geometries) call for significantly expensive mask sets. These masks alone can cost as
much as $1M. Mask generation should be completed in 1–2 weeks, depending on the vendor and the situation.
1.1.6 Silicon Foundry Fabrication (FAB)
Silicon fabrication, in which the wafers are processed and the die are packaged, is another task that is
unambiguously defined but not brief. It can be difficult to influence the delivery schedule of a silicon foundry
significantly. This phase of development can occupy ~8–14 weeks, depending on the technology and the foundry.
1.1.7 Silicon Verification/Functional Check out
Considerable effort goes into confirming that the packaged silicon devices behave as the simulation predicted.
Functional behavior must be verified, and performance must be measured. Thoroughly exhaustive testing can
consume much time and may not be practical. However, it is desirable that a large portion of this work be complete
before system integration and system test proceed. Verification can continue in parallel with other efforts. A
separate board may be designed and built specifically for silicon verification. In all cases, this step depends on the
availability of some form of platform. Additional expenses are associated with this approach, and, though
relatively minor, should be added into the calculations.
1.1.8 Board Design and Fabrication
Ideally, board design and fabrication occur in parallel with silicon fabrication to minimize its impact on the project
schedule. Board design cannot start until a reasonably stable functional specification is available, and it cannot
progress very far until all device pinouts are frozen. In addition to the actual cost of the board fabrication, project
expenses should include the engineering, technical, and administrative head count and the required CAD tools.
Although this total board effort can consume a few months, it can run concurrently with the silicon fabrication
activities.
1.1.9 Board Assembly and Test
Obviously, board assembly cannot be completed until all silicon is received—and it usually must wait for a
moderate degree of silicon verification. After the first few boards are assembled, a progressive series of tests is
necessary to confirm the board design and to verify that manufacturing and assembly steps have not introduced
problems. In some cases, this board is used for silicon verification as well. If a separate board has been designed for
silicon verification, then the same conditions apply. In either case, integration and test depend on assembly and test
of the target board (as opposed to any interim boards designed for silicon verification).
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
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3
The ASIC-Based Solution
1.1.10 Software Integration and Test
There is an assumption that a modem will include some form of processor to provide the necessary control plane
functions. While this processor may be embedded on the ASIC, doing so has a tremendously adverse impact on the
project schedule and greatly increases the complexity, size, power, and so on of the ASIC. This paper does not
address this significantly more complex option.
Efficiency dictates that all control software be written and tested through simulation prior to receipt of the
prototype subsystem hardware. During this stage of development, the ASIC functionality is verified as part of a
larger system. Behavior and performance of the entire subsystems are measured and compared to the original
target. The effort and time required in this phase of the project are large and frequently underestimated. In addition,
once the complete subsystem is verified to be functional and (hopefully) to meet the target specifications, it must
be demonstrated that the subsystem performance complies with all associated standards. This process of
verification with compliance can be extremely expensive, especially if problems must be corrected or if the user
does not have ready access to necessary test facilities. Any deficiencies in design that appear at this stage impose
the risk that changes must be implemented and that the process must return to the logic design phase for a second
iteration.
1.1.11 Ship Prototype Product
Finally, when the prototype product is shipped, the revenue stream can begin. Of course, if errors in the architecture
or design are encountered, this stage is delayed for a re-spin and the process repeats itself, hopefully at an
accelerated pace.
1.2 Total Cost of ASIC-Based Design
Table 1 shows an estimate for the nonrecurring engineering expenses of an ASIC-based design. This estimate is
based on moderate assumptions about the effort required for the phases, and it reveals the high cost of getting the
product ready to ship to customers: 18 months of time and more than $10M, assuming no re-spins.
Table 1. Estimate of Nonrecurring Engineering Expenses for ASIC-Based Solutions
Schedule
(Weeks)
Headcount
(Engineering
Months)
Requirements Definition
8
8
120K
Systems Design
8
16
240K
Logic Design
16
150
2250K
Design Verification
32
300
4500K
2
—
14
8
120K
4
10
150K
12
144K
4
12
144K
10
40
600K
Task
Mask Generation
Fabrication
Silicon Verification
Board Design and Fabrication
Board Assembly and Test
Software Integration and Test
NRE Total
75 Weeks
Cost in Dollars
($180K/Engineering Year)
Comments
Logic design and
verification = 25 weeks
~$750K–$1M for masks
Parallel with silicon
fabrication
~$8.3M Calendar time and
headcount only
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The ASIC-Based Solution
Table 1. Estimate of Nonrecurring Engineering Expenses for ASIC-Based Solutions (Continued)
Schedule
(Weeks)
Task
Headcount
(Engineering
Months)
Cost in Dollars
($180K/Engineering Year)
CAD tools
~$3M
Masks
~$1M
Boards and Comp
Comments
~$0.25M Small quantity only
~$12.5M
TOTAL
1.3 Amortization of ASIC Development Costs
The cost of engineering development detailed in Table 1 must be added to the cost of the ASIC to estimate the real
ownership cost of the ASIC solution. Moreover, we must assess the incremental cost of any re-spin of the device,
including both the cost of producing the second pass silicon and the additional engineering development time.
Assessing the cost of ASIC development to be in the range of $12.5 M and assuming that everything will work as
needed on the first try (both optimistic assumptions), we distribute this $12.5M across the production quantity of
this device. Making another highly optimistic assumption, we expect to ship 10 million voice channel equivalents
based on this solution. We have now added over $1.00 per channel to the cost of the ASIC solution—beyond the
system material costs. Note carefully that this adder is multiplied by the number of unique ASICs required in the
system (for example, if the solution requires two unique ASICS, almost $2.00 per channel is added, and so on.)
1.4 Cost of Being Late to Market
A McKinsey and Company study concluded that the cost of delayed entry into a market can be estimated as shown
in Figure 2.
Maximum Available
Revenue
D = Delay
Maximum Revenue from
Delayed Entry
Time
W
W
Product Life = 2W
Where: Cost = in percentage of opportunity
D = Delay
W = Half of the product lifespan
Cost = D(3W–D)
2W 2
Figure 2. Cost of Delayed Entry into a Market
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
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5
Freescale Solution: Reconfigurable Compute Fabric
Assuming that a Node-B product lifetime is 5 years (60 months) and a delay of 6 months in getting to market, the
cost is a loss of 28 percent of the original revenue estimates. Apparently, the stated advantages of ASIC-based
solutions are much less obvious than many of us have been led to believe. Are there any viable alternatives?
2
Freescale Solution: Reconfigurable Compute Fabric
Efficiently combining an array of compute elements and a configurable interconnect fabric, the Freescale RCF
technology can deliver performance at the levels required by next-generation air interfaces while avoiding the
expenses and schedule delays associated with developing large ASICs.
2.1 Accelerated Development Methodology
Systems designed around Freescale RCF devices permit the user to take advantage of the benefits afforded by an
off-the-shelf solution. Since these solutions are based on standard products instead of custom ASICs, they avoid
the expensive and time-consuming steps of logic design and verification, silicon manufacture, and device test. The
prototype boards can be populated as soon as the boards can be designed and manufactured. Board delivery no
longer occurs at a leisurely pace behind the silicon fabrication. Board delivery now becomes the critical path.
Unlike silicon fabrication, board delivery is a task that offers many opportunities for acceleration—under the
control of a project manager.
The RCF methodology greatly reduces development time because it offers numerous opportunities for parallel
activity. Whereas ASIC-based product development necessarily follows a sequential progression, RCF product
development permits considerable overlap between system design, software development, board
design/manufacture/assembly/test, and system integration/test. The ASIC methodology of Figure 1 is modified as
shown in Figure 3 to yield the RCF methodology shown in Figure 4.
Note: All silicon development steps are omitted.
Requirements
Definition
System
Design
Logic
Design
Design
Verify
Silicon
Fab
Mask
Generation
Board
Design
Silicon
Verify
Board
Assembly/
Test
Software
Integration/
Test
Ship
Prototype
Board
Fab
Figure 3. RCF Modifications to ASIC Methodology
Requirements
Definition
System
Design
Board
Design
Board
Fab
RCF Software
Development
Board
Assembly/
Test
Ship
Prototype
Software
Integration/
Test
Figure 4. Resulting RCF Methodology
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
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Freescale Solution: Reconfigurable Compute Fabric
2.2 Impact of RCF Methodology on Development Cost
As Figure 4 shows, software development can be completed in parallel with the fabrication of the prototype
boards. As with ASIC-based projects, it remains true that system integration and test can consume significant
amounts of time. However, RCF makes it highly probable that any anomalous behavior observed at this stage can
be remedied with a software patch—even after prototype systems ship. Eliminating the silicon manufacturing step
and developing software in parallel with the prototype boards, RCF can reduce project development costs from the
~$12.5M estimated for ASICs to ~$3.9M and also reduce the schedule from ~18 months to ~9 months, as shown in
Table 2.
Table 2. Estimate of Nonrecurring Engineering Expenses for RCF Solutions
Schedule
(Weeks)
Headcount
(Engineering
Months)
Requirements Definition
8
8
120K
Systems Design
8
16
240K
Software Design
16
100
1500K
Board Design and Fabrication
8
12
144K
Board Assembly and Test
4
12
144K
Software Integration and Test
10
50
750K
Task
NRE Total
38 Weeks
CAD tools
Cost in Dollars
($180K/Engineering Year)
~$2.9M
Comments
Software design
concurrent with board
development
Calendar time and
headcount only
~$0.75M
Boards and Comp
TOTAL
~0.25M
38 Weeks
Small quantity only
~$3.9M
2.3 Benefits of RCF Methodology
The many benefits of the RCF methodology are as follows:
•
Reduction in Development Time. Board delivery is the critical path item that determines when
integration and test can complete. With RCF devices, Freescale makes a library of integrated RCF
software modules available. This library of baseband processing functions can form the basis of a
user’s implementation, reducing the development time for basic functionality so developers can focus
on integrating their own intellectual property (IP) into the basic suite where appropriate.
•
Confidence through tested silicon and guaranteed performance. Since the silicon is tested at the
factory with AC and DC performance parameters guaranteed by Freescale, the project team can start
system-level testing immediately upon receipt of the prototype hardware. The team can focus on
developing the solution instead of testing and verifying the silicon components.
•
Reconfigurability supports multiple standards. In today’s cellular market, multiple standards (WCDMA, cdma2000, TD-SCDMA, EDGE, GPRS, etc.) compete for acceptance and position in a
dynamic business environment. The differences in these standards and the inflexibility of ASICs have
forced original equipment manufacturers (OEMs) to design unique modems specifically for each air
interface. Each of the projects has the associated expenses of developing new ASICs.
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
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7
Conclusion
3
•
Common hardware brings larger volumes. While the challenge of building a universal base station yet
remains, RCF provides the flexibility to deliver a single, commercially viable modem design that can
address the needs of all of the air interfaces. RCF therefore permits the OEM to take advantage of the
economies of scale afforded by the combined volumes of multiple markets—a feat that is virtually
impossible with alternative solutions. The benefits of these increased volumes should be taken into
account when the cost of RCF-based solutions is considered. Not only does RCF permit a lower
development cost at an accelerated schedule, but much of the development expense can be distributed
over a greater potential product volume.
•
Competitive system cost, power, and size. The benefits of a reconfigurable approach would be lost if
the target system’s material cost, power consumption, physical size, or channel density were not
competitive. Freescale has put considerable effort into all of these areas, and our RCF devices are
comfortably competitive with alternate approaches in all of these key areas of comparison.
•
Risk Reduction. The standards for next-generation wireless air interfaces are constantly changing and
will continue to do so for many years to come. The market demands must adapt to unforeseen
applications and usage patterns. The flexible architecture of RCF reduces the risk that a design will not
be able to adapt to the new standards/market demands
•
Faster time-to-market. RCF devices are standard, off-the-shelf components. Once the system
architecture and partition are selected, hardware development can began almost immediately. OEMs
can start manufacturing their systems in parallel with the software development effort. Prototype ideas
can be tested in the lab or even in the field and deployed in weeks. Cycle times for development of a
new ASIC are measured in months. ASICs must go through long periods of design validation,
fabrication, silicon verification and testing before system manufacturing can continue. RCF-based
solutions can be developed jointly with systems engineering/software delivery.
•
Longer time in market. As markets evolve and new applications develop, existing ASIC-based systems
require replacement. Their inflexibility renders them unable to serve these new market segments. The
reconfigurability of RCF permits the design of a system to continue as a viable solution because it can
be modified in the field to implement the new services.
•
Potential for new revenue streams. The changes in standards and unforecast market demands for new
features can become a welcome opportunity for OEMs to generate new sources of revenue. Service
providers can offer new services without the need to deploy new hardware. OEMs can enjoy new
revenue streams from existing customers by offering software upgrades to address the new services.
Conclusion
The real cost of ASIC ownership extends far beyond the actual cost of the few mm2 of silicon that is sometimes
used as a metric. A candid and complete comprehensive accounting of all the costs associated with ASIC
development reveals the high costs that often remain unconsidered. These costs must be multiplied by the number
of different ASICs in a system.
The development cycle of ASIC-based solutions follows a serial progression through concept, design, design
verification, fabrication, device test and verification, board/system assembly, system test, and (finally) shipment to
customers (where the revenue stream begins). In contrast, the RCF development cycle eliminates many of these
phases and allows others to be completed in parallel—greatly reducing development time and project costs. ASIC
solutions are inflexible, precluding their applicability to multiple air interfaces unless considerable additional
design effort and superfluous silicon is included in the development project—all at significant incremental expense
and with associated schedule impact.
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
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Freescale Semiconductor
Conclusion
RCF technology lowers the risks incurred from market churn and lowers development costs. RCF technology
yields earlier generation of revenue, longer time generating revenue, the potential for higher volumes through
addressing multiple air interfaces with common hardware. Moreover, RCF technology opens the door to new
sources of revenue for both the service provider and the OEM.
RCF technology yields a competitive edge. It provides a solution that competes with the price and performance of
hardware solutions while offering the benefits of programmability.
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
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9
Conclusion
NOTES:
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
10
Freescale Semiconductor
Conclusion
NOTES:
ASIC Versus Reconfigurable Compute Fabric (RCF) Solutions, Rev. 1
Freescale Semiconductor
11
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ASICRCFWP
Rev. 1
11/2004
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