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Cots Presentation1


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Cots Presentation1

  1. 1. COTS Approach to Military Microprocessor MCMs by Tom Terlizzi Vice President Aeroflex 35 South Service Road Plainview, L.I., N.Y. 11803 Phone: 516.752.2418 FAX: 516.694.6715 email: T2@AEROFLEX.COM ABSTRACT One of the major problems in fielding state of the art Military electronic systems is the lack of militarized electronic components and their swift obsolescence. This paper describes the development of a line of 64 bit MIPS-BasedTM Microprocessor Multi-Chip Modules (MCMs). Solutions and obstacles encountered to support these products for over a decade and the applicability of these solutions to other similar products are described. KEY WORDS: MIPS-BasedTM 64 bit Microprocessor, Multi-Chip Modules (MCMs), Military, obsolescence. Introduction Military Original Equipment Manufacturers (OEMs) are facing a difficult situation in obtaining high performance semiconductor components. Figure 1 illustrates that the percentage of military value will decrease to 0.5% in 2005. This trend is the reason many semiconductor vendors are exiting the Military and Space product markets. The economics cannot support the infrastructure to deal with these products in low volume and low revenue content. Added to this problem is the long life cycle of typical military products. This is not coincident with Moore’s law or the demand for new commercial products as shown in Figure 2. 35% 30% 25% 20% 15% 10% 5% 0% 1955 1975 1995 *2005 Figure 1 - Percentage of U.S. Semiconductor Production Designated for Military Use by Value1 Typical designs and product life cycles for wireless cell phones are at a point where there are two designs per year. However, the volumes for cell phones are in the tens to hundreds of 1. Braun, Ernest and MacDonald, Stuart “Revolution in Miniature - The History and Impact of Semiconductor Electronics”, pp80 (1982). Update Walt Lahti of ICE*. 1
  2. 2. millions per year. While military life cycles are in the order of tens of years and the volumes are in the hundreds to thousands. Table I - MCM Thermal Device Data Die Power Junction θjc Device Size Watts Temp. Rise °C/W (inch) (max) (°C) (max) R4400SC 0.498 x 14 5.78 0.413 Microprocessor 0.707 0.203 3PC218 SRAM x 0.5 1.08 2.16 0.232 0.065 CMOS Buffer x 0.25 2.82 11.28 0.067 Figure 2 - Typical Product Life Cycle Multi Chip Modules Design Considerations In 1992 Aeroflex’s initial military microprocessor MCM was the 1608 a 64-bit MIPS TM RISC Microprocessor with 256K secondary cache memory. It was packaged in a 280 lead ceramic quad flatpack (CQFP) as a custom design with a major military OEM. A photograph with physical dimensions is shown in Figure 3 below. 2.525 MAX R4400 MIPS RISC 85 Spaces at 0.025 Microprocessor Die Pin 226 Pin 141 Pin 227 Pin 140 53 Spaces 1.768 at 0.025 MAX .010 11 each Pin 280 Pin 87 16K x 16 Pin 1 Pin 86 SRAM Die .175 MAX .072 ±.01 .006 Note: Outside ceramic tie bars not shown for clarity. Contains 1,516 Note: Ceramic Tie Bar Wire Bonds Figure 3 - 64 Bit MIPs RISC Microprocessor MCM 1608 Table I lists the key components for the initial design and their attributes. Figure 4 is a simplified block diagram showing the 256K of Level 2 (L2) cache. MIPS is a registered trademark in the United States and other countries, and MIPS32, 4KEc, 4Kp, SOC-it and MIPS-based are trademarks of MIPS Technologies, Inc. 2
  3. 3. SCData(127:0) Secondary SCDchk(15:0) or Level 2 SCDCS SCOE (L2) Cache DQ143-DQ0 CE INTEGER EXECUTION UNIT (9) 16K SCAddr0 A0 General Registers OE by 16 SRAMs ALU/Multiply/Divide Primary or Level 1 DATA/INSTRUCTION Pipeline/Control (L1) Cache CACHE A14:A1 CACHE/MMU WE A15 BWH BWL 16K Byte 16K Byte Instruction Data Cache Cache Cache 48 Entry Control System GND TLB Interface SCAddr MMU (14:1) FLOATING POINT FPU ALU BWH BWL SCAddr 17 Multiply/Divide (2) 16K A15 Square Root by 16 OE SRAMs FP Register CACHE TAG A14:A1 Pipeline Control A0 WE CE DQ0-DQ31 R4400SC/MC Microprocessor SCTag(24:0) SCTCS SCWE SCTchk(6:0) Figure 4 - Simplified Block Diagram of the 64 Bit MIPs RISC Microprocessor MCM 1608 3
  4. 4. Multichip Module Design Considerations Electrical Introduction The electrical requirements for the initial MCMs specified a 66 Mhz clock rate with an estimated 3.0 nanoseconds minimum rise time. The signal path is modeled as a simple R-C series circuit as shown in Figure 5. The 3-db bandwidth can then be related to the pulse rise time of the digital signals of the MCM. Since the system pulse rise time is 3.0 nanoseconds, the required bandwidth is 116.6 MHz. As shown in Figure 6, to reproduce the rise time with minimal distortion (<2%) would require passing the 5th harmonic or 5 x 116.6 MHz or 583.3 MHz. – t ⁄ ( RC ) VOUT V OUT = V ( 1 – e ) V R C R=RESISTANCE OF CONDUCTORS C=CAPACITANCE OF THE SIGNAL PATH 1.00 .95 .90 .85 .80 PERCENTAGE OF FULL VOLTAGE .75 .70 .65 .60 .55 .50 .45 .40 .35 .30 .25 .20 .15 .10 .05 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 2.2 RC TIME IN RC INCREMENTS 0.1 2.3 1 - 1 f3db = -------------- or C MAX = ---------------------------- - 2πRC 2π ( 5f 3db )R 2.2 1 t risetime = 2.2RC = --------------- - C MAX = ------------------------------------------------------------ 2πf 3db 2π × 583.3MHz × 3.75Ω 0.35 t risetime = --------- - f 3db C MAX = 72.6pf Figure 5 - Simple RC Model of MCM Traces 4
  5. 5. For example, the resistance of a circuit with an 8 mil line width which is two inches long can be calculated as follows: l- R = ρ × --- w where: ρ = conductor sheet resistivity l = length of conductor w = width of conductor If the sheet resistivity (ρ) is .015 ohms/❑ , then R = 3.75 ohms. Solving for the maximum capacitance from Figure 5 results in CMAX = 72.6 pf or 36.3 pf/inch or 14.28 pf/cm. 4 Line Capacitance Co (PF/cm) 3 W h 2 t εv h 1 0 4 8 12 16 20 Dielectric Thickness h (mils) Figure 7 - Line Capacitance VS. Dielectric Thickness Thus, the simplified model shows that high temperature alumina cofired ceramic (HTCC) can be used with a two inch conductor run since for a variety of dielectric thickness and conductor widths, the capacitance per unit length is less than 3.0 pf/cm, see Figure 7 (Per typical manufacturer’s data sheet). While other materials with lower dielectric constants are available (See Table II below), only aluminum nitride has better thermal conductivity. However, in 1992 we felt at that time that aluminum nitride had a higher technical risk and no extensive history of military qualification. Therefore, alumina ceramic represented the lowest risk at that time. Table II - Ceramic Material Characteristics Thermal Conductivity Ceramic Technology Dielectric Constant W/m*k Alumina 9.7 - 10.0 17 Aluminum Nitride (AlN) 8.5 150 Low temperature Cofired Ceramic 7.9 2 Mullite 6.8 5 Glass Ceramics (LEC) 5.0 2 5
  6. 6. 40 30 25 20 15 10 9 % ERROR 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 RISE TIME RATIO t = risetime t OUTPUT = t 2 INPUT + t 2SIGNALPATH t INPUT re: if -------------- = t SIGNALPATH 5 t 2INPUT tOUTPUT = t 2 INPUT + ---------------- - 52 1 = t INPUT 1 + ----- - 25 tOUTPUT = tINPUT X 1.019 2% error Figure 6 - Trace Rise Time vs Distortion 6
  7. 7. Propagation Delay and Line Length Using the dielectric constant of alumina as 10 and the formula for propagation delay as: Tpd = 0.0333 × ε in nSec/cm if ε = 10 then Tpd = 0.1 nanoseconds/cm Therefore, for a two inch conductor length, the maximum propagation delay would be: 2 inches x 2.54 cm/inch x .1nanoseconds/cm or 0.508 nanoseconds. Since our signal lines are not terminated in the characteristic impedance of the transmission line, there will be overshoot and ringing. However, if we restrict the line length to be sufficiently short, then the signal will be still rising at time Td (see Figure 9) and the reflections will be part of the rising edge (and also falling edge). With longer lines, the rise of the signal will be completed and reflections will appear as overshoot and undershoot. The maximum unterminated line length results in a maximum 15% ringing2, if the line length is held to: Tr Lmax < ------------------ - 2 × Tpd where Tr = rise time Tpd = propagation delay of line per unit length This assumes that there is no capacitive loading on the line. If capacitive loading is present then the Tpd term must be replaced by T'pd which is calculated as follows. T ′ pd = Tpd ×  1 + Cd ------  -  Co Co = Capacitance ⁄ Length Cd = Capacitive-loading ⁄ Length 2. Kaupp, H.R “Characteristics of Microstrip Transmission lines”, IEEE Transactions on Electronic Computers, Vol. EC-16, No.2, April 1967, pp.185-193 7
  8. 8. For example, if an 8 mil thick dielectric tape and an 8 mil conductor line width are used then the capacitance per unit length is approximately 2.5 pf/cm or 6.35 pf/inch (see Figure 7). If the circuit has six 3 pf loads plus an output load of 10 pf at the receiving end 2 inches from the driver then: ( 18 + 10 )  ----------------------  -  1 + ----------------------  T ′ pd = 0.25nsecs ×  5.08 - 2.5    = 0.25nsecs × 1.79 = 0.447n sec s 3nsecs - L max < ----------------------------------- = 3.35in 2 × 0.447nsecs This is a conservative requirement to meet for most of the MCM signals since the maximum electrical signal length is 1.5quot; - 2quot;. For those signals that are critical, a Spice analysis is performed, as well as insuring that the signal is routed over ground planes to insure microstrip performance. Described below in Figure 8 are typical characteristic impedancee for several dielectric thicknesses. Spice analysis waveforms are shown in Figure 9 for the R4400SC MCM for the SRAM data address lines. Calculated Data 60 4 × 2h Zo = -------- ⋅ ln -------------------------------------- - εγ 0.67 π ( 0.8w + t ) Characteristic Impedance Zo (Ω) 70 60 41.6 W h 50 40 t 30 εv h 20 10 0 4 8 12 16 20 Dielectric Thickness h (mils) Figure 8 - Typical Characteristic Impedances 8
  9. 9. Output of Micro << 15% Shorter Lengths To SRAM Addresses Longer Lengths To SRAM Addresses Td << 15% Figure 9 - Spice Analysis Waveforms Crosstalk The crosstalk between two parallel lines 2 inches long on the same conductor layer is approximated for a 3 nsec rise time as shown in Figure 10. The results indicate approximately a 175mv crosstalk level for an 8 mil line and 8 mil space with an 8 mil dielectric. The capacitance and inductive coupling are approximately 0.4 pf/cm and 1 nH /cm respectively. The crosstalk levels are highly dependent on the driver chip output impedance and loading at the far end. Therefore, the chips must be modeled using the specific device and characteristic output impedance with a Spice simulator. The physical layout was also designed to ensure that adjacent layer signal lines are orthogonal. If there are layers that are not separated by power and ground, two levels away, then they will routed so they are not parallel to minimize coupling. CALCULATED CROSS TALK 300 250 CROSSTALK, mV (FAR END) 200 8 MIL LINE 8 MIL SPACE 150 100 50 0 5 8 10 12 18 Dielectric Thickness h (mils) Figure 10 - Cross Talk vs Dielectric Thickness 9
  10. 10. Decoupling Capacitors The MCM’s circuits can cause significant switching current transients which can cause VCC to drop. When 3.3 volt logic signal levels change 2.5 volts (from a high to a low), the output buffer circuit effectively sees a 40 ohm transmission line impedance. This change in voltage causes an instantaneous output high current change of 62.5 mA. If sixty-four buffers changed simultaneously, the current demand on the power supply would be 4 amps. If less than a 0.1V VCC drop is specified, then we can solve for the decoupling capacitor by using: dv dt ∴ C = I × ----- I = C × ----- - - dt dv C = 4 × 3.0nsecs = 0.12 µ F -------------------- 0.1V C = 0.12 µ F Twenty-three .01µF 0603 ceramic capacitors were used in the MCM for decoupling. Power Distribution The conductor material for high temperature cofired system is tungsten, with a sheet resistivity of 15 milliohms per square maximum. Due to the sheet resistivity of tungsten, the resistance of power and ground must be considered in the design layout stage to insure that there will not be excessive voltage drops within the MCM. Since we provided for fault isolation, in the event that a die shorts out, we routed at least one separate power and ground pin to each row of SRAM die and to the microprocessor. This also has the beneficial effect of reducing the inductance due to the paralleling of several power and ground pins. For the R4400SC, the D.C. current was approximately 3 Amperes. To obtain less than a 1% D.C voltage drop required the trace resistance to be R = V/I or 33mV/3A = 11 milliohms. Evenly splitting the resistance between power and ground yields 5.5 milliohms. Thus, the trace resistance between the power pin and the wirebond pad must be less than 5.5 milliohms to eliminate excessive voltage drops. To achieve this requirement multiple power and ground traces were used on the R4400SC microprocessor die. There are approximately 100 power and ground pins used to distribute the heavy currents within the chip. Thermal Management Using a simplified MCM layout for worst case thermal analysis the results are shown in Figures 11 through 13 and Table I. The simplified finite element model does not show that the die sits in a cavity. This reduces the ceramic thickness to 48mils and an extra “Phantom” die is modeled to make the analysis symmetric. Thus, our thermal resistance numbers are very conservative. 10
  11. 11. 2.5” 0.5 watts each (12x) “Phantom Chip” 1.2 14 Watts 1.5” 0.75 0.3 0.3 0.7 1.25 1.80 2.20 TYPICAL DIE INTERFACE 64 Mils Alumina 20 Mils Silicon 2 Mils Conductive Silver Epoxy Figure 11 - Simplified Module layout for Thermal Analysis Figure 12 - R4400SC MCM, Finite Element Analysis, Thermal Gradients Top View 11
  12. 12. °C C . 36 .36° Figure 13 - R4400SC MCM Finite Element Analysis Cross Sectional Thermal Gradients Mechanical Introduction High temperature cofired ceramic (HTCC) technology offers the lowest risk solution to the R4400SC MCM and is by far the most mature of the emerging MCM technologies. The analysis of thermal constraints, routing density and electrical requirements including maximum signal frequency and minimum rise times reveals that all are within HTCC capability. Additionally, the die rework was a major concern and “Know Good Die” were not available. HTCC is more forgiving to die rework than is organic or silicon substrates. Package Construction The packages is constructed with eight 8 mil thick tape layers resulting in a nominal base thickness of 64 mils. The Microprocessor is centrally located in a cavity approximately 16 mils below the top surface. This improves wirebonding and die thermal conductivity. An integral substrate provides the interconnect between all die and I/O pins. A two tier wire bonding shelf enabled 1 mil aluminum wire bonding to the over 400 pads on a 4.3 mil pitch of the R4400 microprocessor die. A 60 mil high cover seal ring is brazed to the alumina providing the component cavity. All I/O pins are fabricated from Alloy 42 and brazed to the alumina utilizing “dog leg” form. The opposite end of the leads will be attached to a non-conductive alumina ceramic tie bar, to protect the leads from damage in assembly and test. A 15 mil thick cover lid with a 6 mil step is seam welded to the kovar ring frame to provide a hermetic seal. 12
  13. 13. Seal Ring and Seal Ring Metallization The package seal ring material is kovar in accordance with MIL-PRF-38534, Type A. The seal ring dimensions will be 30 mils wide by 60 mils high with a +/- 2 mil tolerance. The seal ring (Figure 14) has an internal corner radius of 30 mils and an external radius of 60 mils. The seal ring metallization will be 70 mils wide and internal and external radii of 60 mils to ensure adequate braze fillets at the corners. This modified geometry has been qualified to aircraft vibration and shock levels with no failures. .135 .030 .045 .020 TYP .010 .050 TYP .060 R .030 R SEAL RING .010 .018 X .045 CONTACT PADS LID ETCHED DOWN TO .005 FOR SEAM WELDING µP .015 Die .175 MAX Cavity .006 .064 See Detail A .048 Detail A Figure 14 - 1608 Package Construction Package Leads The lead frame material is Alloy 42 in accordance with MIL-PRF-38534, Type A. Due to the lead forming anticipated, changes are offered to ensure lead integrity during forming. The leads are 10 mils wide by 6 mils thick and brazed to the alumina in a “dog leg” form on a 18 mil by 45 mil braze pad. This configuration ensures adequate braze fillets around the entire lead. Lid design and deflection Detailed analysis and empirical testing was performed on the final lid design. The 1608 MCM has a nickel plated kovar lid with dimensions 2.315” long by 1.315” wide . The etched kovar lid has a base thickness of 20 mils . The perimeter has a 5 mil flange to provide for seam sealing the hermetic enclosure. Aeroflex uses Rome Air Development Center (RADC) technical report TR-81-382 – “Microcircuit Stress Analysis” as the basis for all lid deflection calculations . This is supplemented by finite element analysis and empirical testing. Using special fixtures and gagues, the actual lid deflection is measured under helium leak test 13
  14. 14. pressures to validate the lid design and analysis. Table III below lists the deflection results versus bomb pressure encountered during fine and gross leak testing per MIL-STD-883. The worst case minimum internal headroom was 20 mils. Thus, a bomb pressure of 15 PSIG was selected to allow a minimum two times safety margin. If the deflection analysis did not meet a 2x safety factor, then ceramic or gold plated kovar spacers would be incorporated into the design. During die attach the spacers would be epoxied or brazed on the top layer of the MCM package. Table III - Lid Deflection vs Leak Test Bomb Pressures Calculated deflection Actual Deflection Bomb Pressure (PSIG (Inch) (Inch) 15 0.007 0.009 30 0.015 0.0155 Obstacles, Obsolescence, and Solutions Introduction After our first die supplier in early 1993 was having difficulty producing the R4400 microprocessor die, Aeroflex was faced with developing multiple and other backup die sources. Fortunately for the project the MIPS R4400 computer architecture was widely available from ten vendors and four were willing to sell die. This accelerated our development of a COTS philosophy prior to Dr. Perry’s edicts in 1994 to use commercial technology in military systems. Component Obsolescence – A Proactive Approach Aeroflex Circuit Technology's (ACT) MIPS microprocessor product line includes a unique Three-Pronged Approach3 to the component obsolescence issues plaguing the military and high-reliability markets: ■ First is to provide cutting edge technology to their target markets ■ Second is to increase product life span by continually enhancing performance while retaining the footprint and pinout compatibility. ■ Third is to provide for an orderly migration path to future products. The GOAL: Take advantage of technological advances in the commercial and industrial component environment. ■ Reduce costs at both the component and system level. ■ Gain access to, “Cutting Edge Technology!” ■ Reduce component and system lead times. The REALITY: Accelerated exposure to component obsolescence for major OEM’s and a new acronym DMS (Diminished Manufacturing Sources). 3. Terlizzi, Tom and Ramos, Frank “Component Obsolescence-A Proactive Approach” COTS-CON 2000 14
  15. 15. COTS products Life Cycles prove to be incompatible with military program Life Cycles and funding requirements; obsolescence increases. As an example of this reality, at a recent DMS conference an OEM complained about the results of a redesign effort to replace obsolete components. Within a year 50% of the new replacement components had obsolescence problems before commencing production. Aeroflex in 1993 developed a long-term plan for this MIPS processor MCM with the following criteria: ■ Mechanical: Select a package style and footprint ■ Electrical: Select a pinout with expansion capabilities and also upward compatible ■ Functional: Evolve the MCM from 256K to 1M of L2 cache Controlling costs and lead-time by design re-use is always one of the primary concerns. We attempt to leverage investments in by keeping the footprint identical: ■ Package Tooling ■ Test Socket tooling ■ Test Software ■ Customer’s next level assembly experience, lead bend fixtures and tooling Up screening of suitable commercially available product provides cutting edge technology quickly to the military OEM: Military Temperature Testing Environmental Screening; including Burn in IE. 4400 179 Pin CPGA 4700 179 Pin CPGA Additionally, by providing the Military OEM product support by “evaluation adapters” which provide a means to evaluate performance increases in their system with real software instead of vague benchmarks (see Figure 15 ). In 1997 Aeroflex made a strategic decision to follow the MIPS Technologies Roadmaps as commercial applications would dictate future MIPS availability. MIPS architecture had 50% of the total RISC market share. Also, MIPS was the highest growth RISC architecture (1997,1998 & 1999) and the only true 64-bit architecture in volume production at the time. Even as we speak, Intel and AMD are now just shipping their first 64 bit machines (early 2003). 15
  16. 16. A CT-52 60P C-P 10-P OD Figure 15 - “Evaluation Adapters” Obsolescence In 1997 we were faced with a major unannounced microprocessor die obsolescence due to a die shrink. The die vendor failed to notify us of their change. With many cofired packages in our stockroom and critical customer delivery schedules at risk a solution was urgently needed. Our solution was to develop a unque interposer which did not degrade the thermal characteristics of the microprocessor die. Our sister division, MIC Technology came to the rescue by developing, very quickly, a “picture frame” thin film multilayer on ceramic interconnect as shown in Figure 16 and 17. This enabled us to get back in to production and we are still shipping these parts today in 2003. We have been fairly sucessful at die banking and last time MCM buys for our OEMs and the government but it always a difficult last minute decsion for all of us. 1 mil Aluminum wire from R4400 microprocessor die to interposer 1 mil gold wire Two tieded wirebonding shelf and pads on MCM cofired package - top layer Figure 16 - Magnified View of Aeroflex’s MIC Technologies Thin Film (“Picture Frame”) Interposer 16
  17. 17. Thin Film “Picture Frame” Interposer Figure 17 - Thin Film “Picture Frame” Interposer In 1999, to further extend the life of the MIPS microprocessor MCMs with L2 cache we introduced the ACT-5271SC. This MCM was co-developed with one of our major OEMs, Quantum Effect Designs (QED), and MIPS Technologies. The 5271SC MCM is shown in Figure 18. QED was later acquired in 2000 by PMC-Sierra. We have continued our licensing agreement for military and high rel market which was started in 1997 with QED. Spin-off products from the initial MCM products were ACT5260PC and ACT7000SC. The microprocessor die, phase lock loop components, decoupling capacitors are all packaged in a 208 CQFP as shown in Figure 19. All these products are footprint and pinout compatible. The only major difference is the core voltage and that the ACT7000SC has L2 cache on board the microprocessor die. Figure 20 shows the ACT7000SC in a cavity down lead bend format on a COTS VME Board. 2 MB SC: (Sync Burst Cache RAM) Cache TAG CPU Cycle FIFO: 2 FPGA RAM Control CPLD Configuration Serial PROM: FPGA PLL CLK Driver MIPS uP: RM5261 Figure 18 - ACT5271SC MCM 17
  18. 18. Figure 19 - ACT5260PC MCM ACT7000SC with cavity down commercial foot-print Figure 20 - Star 7 MVP Militarized COTS VME Bus Single Board Computer 18
  19. 19. Conclusion Aeroflex has developed a COTS approach to Military Microprocessors MCMs for over a decade using a unique synergy of partners as shown in Figure 21. The long product life cycles of Military systems, recently evidenced by the 50th anniversary of the Boeing B-52 bomber, require a different strategy. While there have been many obstacles and obsolescence issues encountered over the last decade, solutions are generated by using electronic design, MCM packaging and business skills. Each of these aspects are important but must be combined for the total economic solution. Figure 21 - Synergy of Partners Summary 1. Robust MCM packaging platform ■ HTCC provides many solutions to electrical, thermal and manufacturing requirements for Military/Aerospace applications. ■ MCM technology offers technology insertion in same footprint 2. Provide Cutting Edge Technology to our Customers ■ Strategic arrangements and licensing agreements provides access to the latest commercial technology ■ Robust MIP Technologies RISC computer architecture provides cost, power savings, and high performance. ■ Hi-Rel Products available within months of the introduction of equivalent Commercial product ■ Provide technical support and software tools using widely available commercial development packages ■ Evaluation adapters allow software benchmarks early in program 19
  20. 20. 3. Increase Product Life Span By: ■ Maintaining IC Package Footprint and Pinout Compatibility to existing products while providing Higher Performance in next generation products ■ Protect large investments in software and application code and quality software testing 4. Provide an Orderly Migration Path to the Future ■ CPU products at various points along the Price/Performance curve ■ Redesign when you need to; Not because you’re forced to by component Acknowlegement The author would like to thank the following people for their valuable insight, help and patience: Paul Carment and Joe LaFiandra. In addition thanks are due to all at PMC-Sierra, MIPS Technologies, and Aeroflex Circuit Technology since the accomplishments summarized in this paper could only result from a team effort. 20