Overview
ABSTRACTINTRODUCTIONFloating point numbers are one possible way of representing real numbers in binary format; the IEEE 754 standard presents two different floating point formats, Binary interchange format and Decimal interchange format. Multiplying floating point numbers is a critical requirement for DSP applications involving large dynamic range. This paper focuses only on single precision normalized binary interchange format. Fig. 1 shows the IEEE 754 single precision binary format representation; it consists of a one bit sign (S), an eight bit exponent (E), and a twenty three bit fraction (M or Mantissa). An extra bit is added to the fraction to form what is called the significand1. If the exponent is greater than 0 and smaller than 255, and there is 1 in the MSB of the significand then the number is said to be a normalized number; in this case the real number is represented by Figure 1. IEEE single precision floating point format?????????Bias = 127.Multiplying two numbers in floating point format is done by 1- adding the exponent of the two numbers then subtracting the bias from their result, 2- multiplying the significand of the two numbers, and 3- calculating the sign by XORing the sign of the two numbers. In order to represent the multiplication result as a normalized number there should be 1 in the MSB of the result (leading one).Floating-point implementation on FPGAs has been the interest of many researchers. In [2], an IEEE 754 single precision pipelined floating point multiplier was implemented on multiple FPGAs (4 Actel A1280). In [3], a custom 16/18 bit three stage pipelined floating point multiplier that doesn’t support rounding modes was implemented. In [4], a single precision floating point multiplier that doesn’t support rounding modes was implemented using a digit-serial multiplier: using the Altera FLEX 8000 it achieved 2.3 MFlops. In [5], a parameterizable floating point multiplier was implemented using the software-like language Handel-C, using the Xilinx XCV1000 FPGA; a five stages pipelined multiplier achieved 28MFlops. In [6], a latency optimized floating point unit using the primitives of Xilinx Virtex II FPGA was implemented with a latency of 4 clock cycles. The multiplier reached a maximum clock frequency of 100 MHz.II. FLOATING POINT MULTIPLICATION ALGORITHMAs stated in the introduction, normalized floating point numbers have the form of Z= (-1S) * 2 (E - Bias) * (1.M). To multiply two floating point numbers the following is done:1. Multiplying the significand; i.e. (1.M1*1.M2)2. Placing the decimal point in the result3. Adding the exponents; i.e. (E1 + E2 – Bias)4. Obtaining the sign; i.e. s1 xor s25. Normalizing the result; i.e. obtaining 1 at the MSB of the results’ significand6. Rounding the result to fit in the available bits7. Checking for underflow/overflow occurrenceConsider a floating point representation similar to the IEEE 754 single precision floating point format, but with a reduced number of mantissa bits (only 4) while still retaining the hidden ‘1’ bit for normalized numbers: A = 0 10000100 0100 = 40, B = 1 10000001 1110 = -7.5To multiply A and B1. Multiply significand: 1.0100 × 1.1110____________ 00000 10100 10100 10100 10100 ____________________ 10010110002. Place the decimal point: 10.010110003. Add exponents: 10000100 + 10000001 _______________ 100000101The exponent representing the two numbers is already shifted/biased by the bias value (127) and is not the true exponent; i.e. EA = EA-true + bias and EB = EB-true + bias And EA + EB = EA-true + EB-true + 2 biasSo we should subtract the bias from the resultant exponent otherwise the bias will be added twice. 100000101 01111111 ________________ 100001104. Obtain the sign bit and put the result together:1 10000110 10.010110005. Normalize the result so that there is a 1 just before the radix point (decimal point). Moving the radix point one place to the left increments the exponent by 1; moving one place to the right decrements the exponent by 1.1 10000110 10.01011000 (before normalizing)1 10000111 1.001011000 (normalized)The result is (without the hidden bit):1 10000111 001011006. The mantissa bits are more than 4 bits (mantissa available bits); rounding is needed. If we applied the truncation rounding mode then the stored value is: 1 10000111 0010.In this paper we present a floating point multiplier in which rounding support isn’t implemented. Rounding support can be added as a separate unit that can be accessed by the multiplier or by a floating point adder, thus accommodating for more precision if the multiplier is connected directly to an adder in a MAC unit. Fig. 2 shows the multiplier structure; Exponents addition, Significand multiplication, and Result’s sign calculation are independent and are done in parallel. The significand multiplication is done on two 24 bit numbers and results in a 48 bit product, which we will call the intermediate product (IP). The IP is represented as (47 downto 0) and thedecimal point is located between bits 46 and 45 in the IP. The following sections detail each block of the floating point multiplier.Figure 2. Floating point multiplier block diagramHARDWARE OF FLOATING POINT MULTIPLIERA. Sign bit calculationMultiplying two numbers results in a negative sign numberiff one of the multiplied numbers is of a negative value. By theaid of a truth table we find that this can be obtained by XORingthe sign of two inputs.B. Unsigned Adder (for exponent addition)This unsigned adder is responsible for adding the exponent of the first input to the exponent of the second input and subtracting the Bias (127) from the addition result (i.e. A_exponent + B_exponent - Bias). The result of this stage is called the intermediate exponent. The add operation is done on 8 bits, and there is no need for a quick result because most of the calculation time is spent in the significand multiplication process (multiplying 24 bits by 24 bits); thus we need a moderate exponent adder and a fast significand multiplier. An 8-bit ripple carry adder is used to add the two input exponents. As shown in Fig. 3 a ripple carry adder is a chain of cascaded full adders and one half adder; each full adder has three inputs (A, B, Ci) and two outputs (S, Co). The carry out (Co) of each adder is fed to the next full adder (i.e each carry bit "ripples" to the next full adder). Ripple Carry AdderThe addition process produces an 8 bit sum (S7 to S0) and a carry bit (Co,7). These bits are concatenated to form a 9 bit addition result (S8 to S0) from which the Bias is subtracted. The Bias is subtracted using an array of ripple borrow subtractors. A normal subtractor has three inputs (minuend (S), subtrahend (T), Borrow in (Bi)) and two outputs (Difference (R), Borrow out (Bo)). The subtractor logic can be optimized if one of its inputs is a constant value which is our case, where the Bias is constant (127|10 = 001111111|2). Table shows the truth table for a 1-bit subtractor with the input T equal to 1 which we will call “one subtractor (OS)” The Boolean equations (2) and (3) represent this subtractor: Figure 4. 1-bit subtractor with the input T = 1Table II shows the truth table for a 1-bit subtractor with the input T equal to 0 which we will call “zero subtractor (ZS)”TABLE II. 1-BIT SUBTRACTOR WITH THE INPUT T = 0The Boolean equations (4) and (5) represent this subtractor:Figure 5. 1-bit subtractor with the input T = 0Fig. 6 shows the Bias subtractor which is a chain of 7 one subtractors (OS) followed by 2 zero subtractors (ZS); the borrow output of each subtractor is fed to the next subtractor. If an underflow occurs then Eresult < 0 and the number is out of the IEEE 754 single precision normalized numbers range; in this case the output is signaled to 0 and an underflow flag isasserted.Figure 6. Ripple Borrow SubtractorC. Unsigned Multiplier (for significand multiplication)This unit is responsible for multiplying the unsigned significand and placing the decimal point in the multiplication product. The result of significand multiplication will be called the intermediate product (IP). The unsigned significand multiplication is done on 24 bit. Multiplier performance should be taken into consideration so as not to affect the whole multiplier’s performance. A 24x24 bit carry save multiplier architecture is used as it has a moderate speed with a simple architecture. In the carry save multiplier, the carry bits are passed diagonally downwards (i.e. the carry bit is propagated to the next stage). Partial products are made by ANDing the inputs together and passing them to the appropriate adder. Carry save multiplier has three main stages:1- The first stage is an array of half adders.2- The middle stages are arrays of full adders. The number of middle stages is equal to the significand size minus two.3- The last stage is an array of ripple carry adders. This stage is called the vector merging stage.The number of adders (Half adders and Full adders) in each stage is equal to the significand size minus one. For example, a 4x4 carry save multiplier is shown in Fig. 7 and it has the following stages:1- The first stage consists of three half adders.2- Two middle stages; each consists of three full adders.3- The vector merging stage consists of one half adder and two full adders.The decimal point is between bits 45 and 46 in the significand multiplier result. The multiplication time taken by the carry save multiplier is determined by its critical path. The critical path starts at the AND gate of the first partial products (i.e. a1b0 and a0b1), passes through the carry logic of the first half adder and the carry logic of the first full adder of the middle stages, then passes through all the vector merging adders. The critical path is marked in bold in Fig. 7 Figure 7. 4x4 bit Carry Save multiplierIn Fig.1- Partial product: aibj = ai and bj2- HA: half adder3- FA: full adderD. NormalizerThe result of the significand multiplication (intermediate product) must be normalized to have a leading ‘1’ just to the left of the decimal point (i.e. in the bit 46 in the intermediate product). Since the inputs are normalized numbers then the intermediate product has the leading one at bit 46 or 47 1- If the leading one is at bit 46 (i.e. to the left of the decimal point) then the intermediate product is already a normalized number and no shift is needed. 2- If the leading one is at bit 47 then the intermediate product is shifted to the right and the exponent is Incremented by 1. The shift operation is done using combinational shift logic made by multiplexers. Fig. 8 shows a simplified logic of a Normalizer that has an 8 bit intermediate product input and a 6 bit intermediate exponent input. Figure 8. Simplified Normalizer logicUNDERFLOW/OVERFLOW DETECTIONOverflow/underflow means that the result’s exponent is too large/small to be represented in the exponent field. The exponent of the result must be 8 bits in size, and must be between 1 and 254 otherwise the value is not a normalized one. An overflow may occur while adding the two exponents or during normalization. Overflow due to exponent addition may be compensated during subtraction of the bias; resulting in a normal output value (normal operation). An underflow may occur while subtracting the bias to form the intermediate exponent. If the intermediate exponent < 0 then it’s an underflow that can never be compensated; if the intermediate exponent = 0 then it’s an underflow that may be compensated during normalization by adding 1 to it. When an overflow occurs an overflow flag signal goes high and the result turns to ±Infinity (sign determined according to the sign of the floating point multiplier inputs). When an underflow occurs an underflow flag signal goes high and the result turns to ±Zero (sign determined according to the sign of the floating point multiplier inputs). Denormalized numbersare signaled to Zero with the appropriate sign calculated from the inputs and an underflow flag is raised. Assume that E1 and E2 are the exponents of the two numbers A and B respectively;the result’s exponent is calculated by (6)Eresult = E1 + E2 - 127 (6)E1 and E2 can have the values from 1 to 254; resulting in Eresult having values from -125 (2-127) to 381 (508-127); but for normalized numbers, Eresult can only have the values from 1 to 254. Table III summarizes the Eresult different values and the effect of normalization on it.PIPELINING THE MULTIPLIERIn order to enhance the performance of the multiplier, three pipelining stages are used to divide the critical path thus increasing the maximum operating frequency of the multiplier.The pipelining stages are imbedded at the following locations:1. In the middle of the significand multiplier, and in the middle of the exponent adder (before the bias subtraction).2. After the significand multiplier, and after the exponent adder.3. At the floating point multiplier outputs (sign, exponent and mantissa bits).Fig. 9 shows the pipelining stages as dotted lines Figure 9. Floating point multiplier with pipelined stagesThree pipelining stages mean that there is latency in the output by three clocks. The synthesis tool “retiming” option was used so that the synthesizer uses its optimization logic to better place the pipelining registers across the critical path.CHAPTER-2INTRODUCTION TO VLSIVery-large-scale integration (VLSI) is the process of creating integrated circuits by combining thousands of transistor-based circuits into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. The term is no longer as common as it once was, as chips have increased in complexity into the hundreds of millions of transistors.OverviewThe first semiconductor chips held one transistor each. Subsequent advances added more and more transistors, and, as a consequence, more individual functions or systems were integrated over time. The first integrated circuits held only a few devices, perhaps as many as ten diodes, transistors, resistors and capacitors, making it possible to fabricate one or more logic gates on a single device. Now known retrospectively as "small-scale integration" (SSI), improvements in technique led to devices with hundreds of logic gates, known as large-scale integration (LSI), i.e. systems with at least a thousand logic gates. Current technology has moved far past this mark and today's microprocessors have many millions of gates and hundreds of millions of individual transistors.At one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like Ultra-large-scale Integration (ULSI) were used. But the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are no longer in widespread use. Even VLSI is now somewhat quaint, given the common assumption that all microprocessors are VLSI or better.As of early 2008, billion-transistor processors are commercially available, an example of which is Intel's Montecito Itanium chip. This is expected to become more commonplace as semiconductor fabrication moves from the current generation of 65 nm processes to the next 45 nm generations (while experiencing new challenges such as increased variation across process corners). Another notable example is NVIDIA’s 280 series GPU.This microprocessor is unique in the fact that its 1.4 Billion transistor count, capable of a teraflop of performance, is almost entirely dedicated to logic (Itanium's transistor count is largely due to the 24MB L3 cache). Current designs, as opposed to the earliest devices, use extensive design automation and automated logic synthesis to lay out the transistors, enabling higher levels of complexity in the resulting logic functionality. Certain high-performance logic blocks like the SRAM cell, however, are still designed by hand to ensure the highest efficiency (sometimes by bending or breaking established design rules to obtain the last bit of performance by trading stability).What is VLSI?VLSI stands for "Very Large Scale Integration". This is the field which involves packing more and more logic devices into smaller and smaller areas.VLSISimply we say Integrated circuit is many transistors on one chip.Design/manufacturing of extremely small, complex circuitry using modified semiconductor materialIntegrated circuit (IC) may contain millions of transistors, each a few mm in sizeApplications wide ranging: most electronic logic devicesHistory of Scale Integrationlate 40s Transistor invented at Bell Labslate 50s First IC (JK-FF by Jack Kilby at TI)early 60s Small Scale Integration (SSI)10s of transistors on a chip late 60s Medium Scale Integration (MSI)100s of transistors on a chipearly 70s Large Scale Integration (LSI)1000s of transistor on a chipearly 80s VLSI 10,000s of transistors on achip (later 100,000s & now 1,000,000s)Ultra LSI is sometimes used for 1,000,000sSSI - Small-Scale Integration (0-102)MSI - Medium-Scale Integration (102-103)LSI - Large-Scale Integration (103-105)VLSI - Very Large-Scale Integration (105-107)ULSI - Ultra Large-Scale Integration (>=107)Advantages of ICs over discrete componentsWhile we will concentrate on integrated circuits , the properties of integrated circuits-what we can and cannot efficiently put in an integrated circuit-largely determine the architecture of the entire system. Integrated circuits improve system characteristics in several critical ways. ICs have three key advantages over digital circuits built from discrete components:Size. Integrated circuits are much smaller-both transistors and wires are shrunk to micrometer sizes, compared to the millimeter or centimeter scales of discrete components. Small size leads to advantages in speed and power consumption, since smaller components have smaller parasitic resistances, capacitances, and inductances.Speed. Signals can be switched between logic 0 and logic 1 much quicker within a chip than they can between chips. Communication within a chip can occur hundreds of times faster than communication between chips on a printed circuit board. The high speed of circuits on-chip is due to their small size-smaller components and wires have smaller parasitic capacitances to slow down the signal.Power consumption. Logic operations within a chip also take much less power. Once again, lower power consumption is largely due to the small size of circuits on the chip-smaller parasitic capacitances and resistances require less power to drive them.VLSI and systemsThese advantages of integrated circuits translate into advantages at the system level:Smaller physical size. Smallness is often an advantage in itself-consider portable televisions or handheld cellular telephones.Lower power consumption. Replacing a handful of standard parts with a single chip reduces total power consumption. Reducing power consumption has a ripple effect on the rest of the system: a smaller, cheaper power supply can be used; since less power consumption means less heat, a fan may no longer be necessary; a simpler cabinet with less shielding for electromagnetic shielding may be feasible, too.Reduced cost. Reducing the number of components, the power supply requirements, cabinet costs, and so on, will inevitably reduce system cost. The ripple effect of integration is such that the cost of a system built from custom ICs can be less, even though the individual ICs cost more than the standard parts they replace.Understanding why integrated circuit technology has such profound influence on the design of digital systems requires understanding both the technology of IC manufacturing and the economics of ICs and digital systems.ApplicationsElectronic system in cars.Digital electronics control VCRsTransaction processing system, ATMPersonal computers and WorkstationsMedical electronic systems.Etc….Applications of VLSIElectronic systems now perform a wide variety of tasks in daily life. Electronic systems in some cases have replaced mechanisms that operated mechanically, hydraulically, or by other means; electronics are usually smaller, more flexible, and easier to service. In other cases electronic systems have created totally new applications. Electronic systems perform a variety of tasks, some of them visible, some more hidden:Personal entertainment systems such as portable MP3 players and DVD players perform sophisticated algorithms with remarkably little energy.Electronic systems in cars operate stereo systems and displays; they also control fuel injection systems, adjust suspensions to varying terrain, and perform the control functions required for anti-lock braking (ABS) systems.Digital electronics compress and decompress video, even at high-definition data rates, on-the-fly in consumer electronics.Low-cost terminals for Web browsing still require sophisticated electronics, despite their dedicated function.Personal computers and workstations provide word-processing, financial analysis, and games. Computers include both central processing units (CPUs) and special-purpose hardware for disk access, faster screen display, etc.Medical electronic systems measure bodily functions and perform complex processing algorithms to warn about unusual conditions. The availability of these complex systems, far from overwhelming consumers, only creates demand for even more complex systems.The growing sophistication of applications continually pushes the design and manufacturing of integrated circuits and electronic systems to new levels of complexity. And perhaps the most amazing characteristic of this collection of systems is its variety-as systems become more complex, we build not a few general-purpose computers but an ever wider range of special-purpose systems. Our ability to do so is a testament to our growing mastery of both integrated circuit manufacturing and design, but the increasing demands of customers continue to test the limits of design and manufacturingASICAn Application-Specific Integrated Circuit (ASIC) is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. For example, a chip designed solely to run a cell phone is an ASIC. Intermediate between ASICs and industry standard integrated circuits, like the 7400 or the 4000 series, are application specific standard products (ASSPs).As feature sizes have shrunk and design tools improved over the years, the maximum complexity (and hence functionality) possible in an ASIC has grown from 5,000 gates to over 100 million. Modern ASICs often include entire 32-bit processors, memory blocks including ROM, RAM, EEPROM, Flash and other large building blocks. Such an ASIC is often termed a SoC (system-on-a-chip). Designers of digital ASICs use a hardware description language (HDL), such as Verilog or VHDL, to describe the functionality of ASICs.Field-programmable gate arrays (FPGA) are the modern-day technology for building a breadboard or prototype from standard parts; programmable logic blocks and programmable interconnects allow the same FPGA to be used in many different applications. For smaller designs and/or lower production volumes, FPGAs may be more cost effective than an ASIC design even in production.An application-specific integrated circuit (ASIC) is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. A Structured ASIC falls between an FPGA and a Standard Cell-based ASIC Structured ASIC’s are used mainly for mid-volume level designs The design task for structured ASIC’s is to map the circuit into a fixed arrangement of known cellsINTRODUCTION TO XILINXMigrating Projects from Previous ISE Software ReleasesWhen you open a project file from a previous release, the ISE? software prompts you to migrate your project. If you click Backup and Migrate or Migrate Only, the software automatically converts your project file to the current release. If you click Cancel, the software does not convert your project and, instead, opens Project Navigator with no project loaded.Note?After you convert your project, you cannot open it in previous versions of the ISE software, such as the ISE 11 software. However, you can optionally create a backup of the original project as part of project migration, as described below.To Migrate a ProjectIn the ISE 12 Project Navigator, select File > Open Project.In the Open Project dialog box, select the .xise file to migrate.Note?You may need to change the extension in the Files of type field to display .npl (ISE 5 and ISE 6 software) or .ise (ISE 7 through ISE 10 software) project files.In the dialog box that appears, select Backup and Migrate or Migrate Only.The ISE software automatically converts your project to an ISE 12 project.Note?If you chose to Backup and Migrate, a backup of the original project is created at project_name_ise12migration.zip.Implement the design using the new version of the software.Note?Implementation status is not maintained after migration.PropertiesFor information on properties that have changed in the ISE 12 software, see ISE 11 to ISE 12 Properties Conversion.IP ModulesIf your design includes IP modules that were created using CORE Generator? software or Xilinx? Platform Studio (XPS) and you need to modify these modules, you may be required to update the core. However, if the core netlist is present and you do not need to modify the core, updates are not required and the existing netlist is used during implementation.Obsolete Source File TypesThe ISE 12 software supports all of the source types that were supported in the ISE 11 software.If you are working with projects from previous releases, state diagram source files (.dia), ABEL source files (.abl), and test bench waveform source files (.tbw) are no longer supported. For state diagram and ABEL source files, the software finds an associated HDL file and adds it to the project, if possible. For test bench waveform files, the software automatically converts the TBW file to an HDL test bench and adds it to the project. To convert a TBW file after project migration, see Converting a TBW File to an HDL Test Bench.Migrating Projects from Previous ISE Software ReleasesWhen you open a project file from a previous release, the ISE? software prompts you to migrate your project. If you click Backup and Migrate or Migrate Only, the software automatically converts your project file to the current release. If you click Cancel, the software does not convert your project and, instead, opens Project Navigator with no project loaded.Note?After you convert your project, you cannot open it in previous versions of the ISE software, such as the ISE 11 software. However, you can optionally create a backup of the original project as part of project migration, as described below.To Migrate a ProjectIn the ISE 12 Project Navigator, select File > Open Project.In the Open Project dialog box, select the .xise file to migrate.Note?You may need to change the extension in the Files of type field to display .npl (ISE 5 and ISE 6 software) or .ise (ISE 7 through ISE 10 software) project files.In the dialog box that appears, select Backup and Migrate or Migrate Only.The ISE software automatically converts your project to an ISE 12 project.Note?If you chose to Backup and Migrate, a backup of the original project is created at project_name_ise12migration.zip.Implement the design using the new version of the software.Note?Implementation status is not maintained after migration.PropertiesFor information on properties that have changed in the ISE 12 software, see ISE 11 to ISE 12 Properties Conversion.IP ModulesIf your design includes IP modules that were created using CORE Generator? software or Xilinx? Platform Studio (XPS) and you need to modify these modules, you may be required to update the core. However, if the core netlist is present and you do not need to modify the core, updates are not required and the existing netlist is used during implementation.Obsolete Source File TypesThe ISE 12 software supports all of the source types that were supported in the ISE 11 software.If you are working with projects from previous releases, state diagram source files (.dia), ABEL source files (.abl), and test bench waveform source files (.tbw) are no longer supported. For state diagram and ABEL source files, the software finds an associated HDL file and adds it to the project, if possible. For test bench waveform files, the software automatically converts the TBW file to an HDL test bench and adds it to the project. To convert a TBW file after project migration, see Converting a TBW File to an HDL Test Bench.Using ISE Example ProjectsTo help familiarize you with the ISE? software and with FPGA and CPLD designs, a set of example designs is provided with Project Navigator. The examples show different design techniques and source types, such as VHDL, Verilog, schematic, or EDIF, and include different constraints and IP.To Open an ExampleSelect File > Open Example.In the Open Example dialog box, select the Sample Project Name.Note?To help you choose an example project, the Project Description field describes each project. In addition, you can scroll to the right to see additional fields, which provide details about the project.In the Destination Directory field, enter a directory name or browse to the directory.Click OK.The example project is extracted to the directory you specified in the Destination Directory field and is automatically opened in Project Navigator. You can then run processes on the example project and save any changes.Note?If you modified an example project and want to overwrite it with the original example project, select File > Open Example, select the Sample Project Name, and specify the same Destination Directory you originally used. In the dialog box that appears, select Overwrite the existing project and click OK.Creating a ProjectProject Navigator allows you to manage your FPGA and CPLD designs using an ISE? project, which contains all the source files and settings specific to your design. First, you must create a project and then, add source files, and set process properties. After you create a project, you can run processes to implement, constrain, and analyze your design. Project Navigator provides a wizard to help you create a project as follows.Note?If you prefer, you can create a project using the New Project dialog box instead of the New Project Wizard. To use the New Project dialog box, deselect the Use New Project wizard option in the ISE General page of the Preferences dialog box. To Create a ProjectSelect File > New Project to launch the New Project Wizard.In the Create New Project page, set the name, location, and project type, and click Next.For EDIF or NGC/NGO projects only: In the Import EDIF/NGC Project page, select the input and constraint file for the project, and click Next.In the Project Settings page, set the device and project properties, and click Next.In the Project Summary page, review the information, and click Finish to create the project.Project Navigator creates the project file (project_name.xise) in the directory you specified. After you add source files to the project, the files appear in the Hierarchy pane of the Design panel. Project Navigator manages your project based on the design properties (top-level module type, device type, synthesis tool, and language) you selected when you created the project. It organizes all the parts of your design and keeps track of the processes necessary to move the design from design entry through implementation to programming the targeted Xilinx? device.Note?For information on changing design properties, see Changing Design Properties.You can now perform any of the following: Create new source files for your project. Add existing source files to your project. Run processes on your source files. Modify process properties. Creating a Copy of a ProjectYou can create a copy of a project to experiment with different source options and implementations. Depending on your needs, the design source files for the copied project and their location can vary as follows:Design source files are left in their existing location, and the copied project points to these files.Design source files, including generated files, are copied and placed in a specified directory.Design source files, excluding generated files, are copied and placed in a specified directory.Copied projects are the same as other projects in both form and function. For example, you can do the following with copied projects:Open the copied project using the File > Open Project menu command.View, modify, and implement the copied project.Use the Project Browser to view key summary data for the copied project and then, open the copied project for further analysis and implementation, as described in Using the Project Browser.Note?Alternatively, you can create an archive of your project, which puts all of the project contents into a ZIP file. Archived projects must be unzipped before being opened in Project Navigator. For information on archiving, see Creating a Project Archive.To Create a Copy of a ProjectSelect File > Copy Project.In the Copy Project dialog box, enter the Name for the copy.Note?The name for the copy can be the same as the name for the project, as long as you specify a different location.Enter a directory Location to store the copied project.Optionally, enter a Working directory.By default, this is blank, and the working directory is the same as the project directory. However, you can specify a working directory if you want to keep your ISE? project file (.xise extension) separate from your working area.Optionally, enter a Description for the copy.The description can be useful in identifying key traits of the project for reference later.In the Source options area, do the following:Select one of the following options:Keep sources in their current locations - to leave the design source files in their existing location.If you select this option, the copied project points to the files in their existing location. If you edit the files in the copied project, the changes also appear in the original project, because the source files are shared between the two projects.Copy sources to the new location - to make a copy of all the design source files and place them in the specified Location directory.If you select this option, the copied project points to the files in the specified directory. If you edit the files in the copied project, the changes do not appear in the original project, because the source files are not shared between the two projects.Optionally, select Copy files from Macro Search Path directories to copy files from the directories you specify in the Macro Search Path property in the Translate Properties dialog box. All files from the specified directories are copied, not just the files used by the design.Note?If you added a netlist source file directly to the project as described in Working with Netlist-Based IP, the file is automatically copied as part of Copy Project because it is a project source file. Adding netlist source files to the project is the preferred method for incorporating netlist modules into your design, because the files are managed automatically by Project Navigator.Optionally, click Copy Additional Files to copy files that were not included in the original project. In the Copy Additional Files dialog box, use the Add Files and Remove Files buttons to update the list of additional files to copy. Additional files are copied to the copied project location after all other files are copied.To exclude generated files from the copy, such as implementation results and reports, select Exclude generated files from the copy.When you select this option, the copied project opens in a state in which processes have not yet been run.To automatically open the copy after creating it, select Open the copied project.Note?By default, this option is disabled. If you leave this option disabled, the original project remains open after the copy is made.Click OK.Creating a Project ArchiveA project archive is a single, compressed ZIP file with a .zip extension. By default, it contains all project files, source files, and generated files, including the following:User-added sources and associated filesRemote sourcesVerilog `include filesFiles in the macro search pathGenerated filesNon-project filesTo Archive a ProjectSelect Project > Archive.In the Project Archive dialog box, specify a file name and directory for the ZIP file.Optionally, select Exclude generated files from the archive to exclude generated files and non-project files from the archive.Click OK.A ZIP file is created in the specified directory. To open the archived project, you must first unzip the ZIP file, and then, you can open the project.Note?Sources that reside outside of the project directory are copied into a remote_sources subdirectory in the project archive. When the archive is unzipped and opened, you must either specify the location of these files in the remote_sources subdirectory for the unzipped project, or manually copy the sources into their original location. INTRODUCTION TO VERILOG HDL What is HDL A typical Hardware Description Language (HDL) supports a mixed-level description in which gate and netlist constructs are used with functional descriptions. This mixed-level capability enables you to describe system architectures at a high level of abstraction, then incrementally refine a design’s detailed gate-level implementation. HDL descriptions offer the following advantages: ? We can verify design functionality early in the design process. A design written as an HDL description can be simulated immediately. Design simulation at this high level — at the gate-level before implementation — allows you to evaluate architectural and design decisions. ? An HDL description is more easily read and understood than a netlist or schematic description. HDL descriptions provide technology-independent documentation of a design and its functionality. Because the initial HDL design description is technology independent, you can use it again to generate the design in a different technology, without having to translate it from the original technology. ? Large designs are easier to handle with HDL tools than schematic tools. Verilog Overview : Introduction Verilog is a HARDWARE DESCRIPTION LANGUAGE (HDL). A hardware description Language is a language used to describe a digital system, for example, a microprocessor or a memory or a simple flip-flop. This just means that, by using a HDL one can describe any hardware (digital ) at any level. Verilog provides both behavioral and structural language structures. These structures allow expressing design objects at high and low levels of abstraction. Designing hardware with a language such as Verilog allows using software concepts such as parallel processing and object-oriented programming. Verilog has a syntax similar to C and Pascal. Design Styles Verilog like any other hardware description language permits the designers to create a design in either Bottom-up or Top-down methodology. Bottom-Up Design The traditional method of electronic design is bottom-up. Each design is performed at the gate-level using the standard gates. With increasing complexity of new designs this approach is nearly impossible to maintain. New systems consist of ASIC or microprocessors with a complexity of thousands of transistors. These traditional bottom-up designs have to give way to new structural, hierarchical design methods. Without these new design practices it would be impossible to handle the new complexity. Top-Down Design The desired design-style of all designers is the top-down design. A real top-down design allows early testing, easy change of different technologies, a structured system design and offers many other advantages. But it is very difficult to follow a pure top-down design. Due to this fact most designs are mix of both the methods, implementing some key elements of both design styles. Complex circuits are commonly designed using the top down methodology. Various specification levels are required at each stage of the design process. Abstraction Levels of Verilog Verilog supports a design at many different levels of abstraction. Three of them are very important: ?Behavioral level ?Register-Transfer Level Gate Level Behavioral level This level describes a system by concurrent algorithms (Behavioral). Each algorithm itself is sequential, that means it consists of a set of instructions that are executed one after the other. Functions, Tasks and Always blocks are the main elements. There is no regard to the structural realization of the design. Register-Transfer Level Designs using the Register-Transfer Level specify the characteristics of a circuit by operations and the transfer of data between the registers. An explicit clock is used. RTL design contains exact timing possibility; operations are scheduled to occur at certain times. Modern definition of a RTL code is "Any code that is synthesizable is called RTL code". Gate Level Within the logic level the characteristics of a system are described by logical links and their timing properties. All signals are discrete signals. They can only have definite logical values (`0', `1', `X', `Z`). The usable operations are predefined logic primitives (AND, OR, NOT etc gates). Using gate level modeling might not be a good idea for any level of logic design. Gate level code is generated by tools like synthesis tools and this Netlist is used for gate level simulation and for backend. vlsi design flowIntroduction Design is the most significant human endeavor: It is the channel through which creativity is realized. Design determines our every activity as well as the results of those activities; thus it includes planning, problem solving, and producing. Typically, the term "design" is applied to the planning and production of artifacts such as jewelry, houses, cars, and cities. Design is also found in problem-solving tasks such as mathematical proofs and games. Finally, design is found in pure planning activities such as making a law or throwing a party. More specific to the matter at hand is the design of manufacturable artifacts. This activity uses all facets of design because, in addition to the specification of a producible object, it requires the planning of that object's manufacture, and much problem solving along the way. Design of objects usually begins with a rough sketch that is refined by adding precise dimensions. The final plan must not only specify exact sizes, but also include a scheme for ordering the steps of production. Additional considerations depend on the production environment; for example, whether one or ten million will be made, and how precisely the manufacturing environment can be controlled. A semiconductor process technology is a method by which working circuits can be manufactured from designed specifications. There are many such technologies, each of which creates a different environment or style of design. SOURCE CODE AND RESULTSCONCLUSIONS ANS FUTURESCOPEThis paper presents an implementation of a floating point multiplier that supports the IEEE 754-2008 binary interchange format; the multiplier doesn’t implement rounding and just presents the significand multiplication result as is (48 bits); this gives better precision if the whole 48 bits are utilized in another unit; i.e. a floating point adder to form a MAC unit. The design has three pipelining stages and after implementation on a Xilinx Virtex5 FPGA it achieves 301 MFLOPs. ................
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