ARROWS USER MANUAL - Michael Wieckowski
Contents
1. axs VLSI TOOLS ARROWS USER MANUAL 13 47 portlessCell inputsOutputs power vdd 48 portlessCell inputsOutputs ground Q 49 Lines 50 through 73 perform the same analysis instantiation execution and visualization as in the quick start example 50 The actual analysis is a VectorField analysis object 51 Initialize this object using our SRAM object technology etc 52 The bistableNodes are a list of the 2 nodes considered in the state space 53 The numberOfSteps is the quantization parameter for the state space 54 analysis arrows VectorField cellToAnalyze sixCell 55 bistableNodes data dataBar 56 technologyToUse amiTechnology DZ numberOfSteps 50 58 environmentToUse analysisEnv 59 testbenchToUse testbench 60 analysis runVectorFieldSim 61 analysis parseVectorFieldSim 62 analysis findNullclines 63 HH FK gt gt K gt K K K K K K KK OK K K KK KK KK KKK KKK Now Create some output to look at FK K K K K K K K K K K K KK gt K K K K K K KKK 64 65 Calculate the SNM as the least square fitting in the butterfly curve 66 print SNM Vectors repr analysis calculateSnm 67 myVectorPlot arrows VectorPlot analysis analysisEnv 68 myVectorPlot setHexColor 3E6BCE 69 myVectorPlot drawNullclineUC 70 myVectorPlot drawNullclineVC 71 myVectorPlot setHexColor FCA12C 72 myVectorPlot drawSnmRulers 73 Lines 74 through 89 swap out t2. drawNullclineU drawNulclineV e Description e Draws the nullclines U or V on the vectorfield e Arguments None e Return None drawSnmRulers e Description e Draws the boxes and diagonals for the SNM largest square methods e Arguments None e Return None drawMetastablePoint e Description e Places a dot at the metastable point calculated in the vector field e Arguments None e Return None drawSeparatrix e Description e Draws the separatrix points on the vector field e Arguments None e Return None createEps fileName e Description e Exports the PyX graph as an EPS file e Arguments e fileName is a string path to the output filename e Return None createPdf fileName e Description e Exports the PyX graph as a PDF file e Arguments e fileName is a string path to the output filename e Return None VLSI TOOLS ARROWS USER MANUAL 26
3. This class is the main visualization tool for Arrows When linked with a VectorField class it sup ports plotting of bistable state spaces nullclines SNM rulers serparatrix traces etc using the Py thon package PyX Relevant properties vectorField e Description e A VectorField object to be visualized environmentToUse VESI TOOLS ARROWS USER MANUAL 24 e Description e An Environment object used to determine the extents of the state space boundary from the globalSupply property xLabel yLabel e Description e Strings used to label the axis of the state space Relevant methods _ init_ vectorFieldAnalysis environmentToUse xLabel yLabel e Description e Constructor method e Arguments e vectorFleldAnalysis is the VectorField object to visualize e environmentToUse is the Environment object associated with the analysis e xLabel and yLabel are optional strings used to generate the plots e Return None getGraph e Description e Utility method used to get the internal representation of the vector field plot This method is used when you have two different VectorPlot objects and you want to combine their data Used in conjunction with the setGraph method e Arguments None e Return A PyX graph object setGraph graphToUse e Description e Utility method used to set the internal representation of the vector field plot This method is used when you have two different VectorPlot objects and
4. ple Arrows scrips at the same time The AMI600 technology object is created and initialized in Line 18 It specifies the name of the technology as well as the version The vendor node and version are concatenated internally to generate a unique identifier for the technology in the tech xml file For info on the tech xml file check the section above entitled Configuring tech xml Line 22 simply tells the technology object to go ahead and scan the XML file for devices models formats etc Since the AMI tech nology does not contain special models or devices for voltage sources we also include a ge neric technology which defines these basic circuit elements VLSI TOOLS ARROWS USER MANUAL import arrows from datetime import FKK K K gt k K K K K RK K K K K K K K K K K K K K K K K K KK FK gt gt gt K K KK K K K K K K K K K K K K K K K K K K KK KK KK KK K K gt K K K K K K K K K K K K K K K K K KKK gt gt gt 2K K 5 6 Set up the analysis environment This is where you 7 specify a uniqueId to your controller so that 8 it won t overwrite other files and you can run multiple 9 at the same time Also specify the global 10 supply voltage 11 idViaDate str datetime now month str datetime now day str datetime now Q year 12 analysisEnv arrows Environment uniqueld idViaDate 13 globalSupply 5 0 15 to generate the netlists we use Technology objects which are con
5. Cell Node Bar CellNodeBar bo ro w on 0 0 2 0 4 0 6 0 8 1 0 l CellNode CellN ode VLSI TOOLS ARROWS USER MANUAL Setup Process technology independence and user independence is a MUST for any successful VLSI project To that end I recommend setting up your design environment as shown in the following figure In essence all design kits and tools are installed in isolated locations to be shared among all users Each user maintains separate directories for each of their projects where each directory has a shell script to link the required tools for that project only The following setup instructions for Arrows are based on this model Installing Python Since Arrows is a tool for layout scripting in Python it requires a recent version of Python to be in stalled 2 6 or higher Most linux distributions will have a version of Python installed for you to use but the version may not be recent enough Luckily you can install a local copy of Python on top of any existing installations if the machine you want to run on doesn t meet the requirements I rec ommend installing a copy of Python 2 6 locally as follows 1 Download Python via SVN and decompress it as follows 1 1 cd some tempPath 1 2 wget http www python org ftp python 2 6 1 Python 2 6 1 tgz 1 3 tar xvzf Python 2 6 1 tgz 2 Install Python into your home directory or a project directory 2 1 cd some tempPath Python 2 6 1 2 2 configure
6. Constructor method e Arguments e vendor node and version are string objects used to identify a particular technology defi nition in an XML file by concatenating all three into a single string internally e environmentToUse is an Environment object e Return None generateModellncludeFile e Description e Creates a file for inclusion in a simulation The file contains all of the model paths for a particular technology e Return None device name format properties e Description e Creates a string for instantiating a device for this technology node into a netlist e Arguments e name isa unique name string to identify the device in a netlist e fotmat is a string specifying which netlist format to use Currently spectre is the only option e properties is a dictionary of properties and values corresponding to the device definition in the tech xml file VLSI TOOLS ARROWS USER MANUAL 19 e Return None Testbench Class This class encapsulates the testbench used when running vector field analysis It requires a technol ogy object and stores statements internally to instantiate testbench elements such as voltage and current sources Relevant properties technologyToUse e Description e A Technology object from which basic circuit elements can be instantiated Relevant methods _init_ technologyToUse e Description e Constructor method e Arguments e technologyToUse is the Technology object whose
7. e Description e Calculates the euclidian distance from any point to the separatrix e Arguments pointToMeasureFrom is a float tuple of coordinates e Return A float of the distance in state space units volts distance ToMetastable pointToMeasureFrom e Description e Calculates the euclidian distance from the metstable point to any provided point within the state space boundaries e Arguments pointToMeasureFrom is a float tuple of coordinates e Return A float of the distance in state space units volts integrateSeparatrix e Description e Calculates the integral of the state space underneath the separatrix e Arguments None e Return A float integral value weightedDistanceToSeparatrix pointToMeasureFrom e Description e Calculates the weighted distance from any point to its closest separatrix point using the U V data in the vector field This is the method used to calculate Separatrix Affinity when the pointToMeasureFrom is specified as one of the stable points e Arguments pointToMeasureFrom is a float tuple of coordinates e Return A float of the weighted distance from the measurement point to the separatrix point weightedDistanceToMetastable pointToMeasureFrom e Description e Calculates the weighted distance from any point to the metastable point using the U V data in the vector field e Arguments pointToMeasureFrom is a float tuple of coordinates e Return A float of the weighted distance VectorPlot Class
8. point calculated via the intersection of the U and V null clines Since nullclines intersect at 3 points for a bistable system it is assumed that the metastable point is that point whose x and y coordinates are most similar defines the point most central in the state space stablePointA stablePointB e Description e Two float tuples providing the coordinates of the two stable points calculated using nullcline intersection See metastable point above separatrixPoints e Description e Alist of tuples containing x y coordinates for separatrix points Since the separatrix is interpolated these points are not necessarily in the X Y coordinate list snmRulers e Description e Alist of ruler coordinates largest box inside of butterfly curve Each ruler is a float tu ple of the form x1 y1 x2 y2 providing the coordinates of the SNM box snms e Description e Alist of the SNMs noise margins for each lobe of the butterfly curve using the largest square method The smallest of these two list elements defines the SNM of the system Relevant methods _init_ cellToAnalyse bistableNodes technologyToUse numberOfSteps environmentToUse test benchToUse e Description e Constructor method e Arguments e cellToAnalyze technologyToUse environmentToUse testBenchToUse are self explanatory Each of these objects is passed in during initialization to control the terms of the analy sis e bistableNodes is a string list of the bis
9. prefix some localPath forPython toReside VLSI TOOLS ARROWS USER MANUAL 2 3 make 2 4 make install Installing Arrows These instructions will install Arrows into a central location 1 2 5 6 Download the Arrows zip from http www vlsitools com mkdir design common Arrows mv download location Arrows_1 0 zip design common Arrows cd design common Arrows unzip Arrows_1 0 zip rm Arrows_1 0 zip The remainder of the installation involves copying and modifying the shell script in design common Arrows exampleUserDir This is covered in the section Setup a directory to work from below Installing the NCSU CDK All the examples in this manual are based on the NCSU Cadence Design Kit Since it is freely available it is a good platform to introducing Arrows while avoiding any IP issues Arrows will work with ANY technology and is designed specifically to do so The following steps were used to install the NCSU CDK on my system yours might be different so read carefully 1 Register and download the CDK from http www eda ncsu edu wiki NCSU CDK download I consider it good practice to keep the CDK itself in a central location that is referenced by each user s working directory Untar Unzip the downloaded CDK into your central loca tion For my case 2 1 cp ncsu cdk 1 5 1 tar gz design common 2 2 cd design common 2 3 tar xvvzf ncsu cdk 1 5 1 tar g
10. K KK KK KKK KK KK KKK KK KK KKK KK KK KKK KKK K FK K KKK 2K K FK K KKK 2K K 2K K K K 5 Notice this time we just use a string as our unique ID 6 analysisEnv arrows Environment uniqueld parameterExample 7 globalSupply 5 0 8 9 amiTechnology arrows Technology vendor Ami 10 node 600 11 version a 12 environmentToUse analysisEnv 13 amiTechnology configureFromXm1L 14 genericTechnology arrows Technology vendor Generic 15 node 16 version 17 environmentToUse analysisEnv 18 genericTechnology configureFromXmL 19 20 sixCell arrows Circuit technologyToUse amiTechnology 21 sixCell configureFromXml CanalysisEnv modelPath circuits sramCell6T xmL 22 23 testbench arrows Testbench technologyToUse genericTechnology make a new testbench here 24 25 Now set up the testbench connections to the cells 26 sixCell inputsOutputs LeftBitline vdd vdd for standby for write 27 sixCell inputsOutputs rightBitline vdd 28 sixCell inputs0utputs wordline vdd do a read SNM this time 29 sixCell inputsOutputs power vdd 30 sixCell inputsOutputs ground 0 31 32 The actual analysis is a VectorField analysis object 33 Initialize this object using our SRAM object technology etc 34 The bistableNodes are a list of the 2 nodes considered in the state space 35 The numberOfSteps is the quantization parameter for the st
11. V L S I T O O L S www vlsitools com ARROWS USER MANUAL Version 1 0 AUTHOR Michael Wieckowski CONTACT wieckows umich edu www vlsitools com Introduction What is Arrows Arrows is a Python scripting package for performing vector field dynamical analysis on bistable circuits using the Spectre simulator Arrows is highly object oriented and abstracted allowing for complete independence of circuit structure technology node environment and analysis type This allows Arrows to perform black box analysis of any bistable circuit design for SRAM cells to e Generate butterfly curves e Calculate noise margins e Trace separatrix lines e Perform dynamic stability analysis e Calculate the Separatrix Affinity metric e Visualize quasi transient simulations Two examples are shown in the figures below One of the primary goals of Arrows is to be highly extensible while maintaining independence of technology and circuit topology To that end circuit structures and technology nodes design kits are modeled and wrapped in customizable XML files The resulting design framework makes Ar rows highly readable easy to learn and implement and well suited to large multi user projects Arrows is being developed rapidly and new features are being added daily In addition I welcome any feedback and feature requests from the VLSI community so don t hesitate to ask if you think function X is a must have ao
12. and SNM calcu lations for both cells are plotted on the same state space graph for easy comparison The Arrows Overlay Script Lines 1 through 22 are the same as in the previous example The environment AMI600 technol ogy and generic technology objects are all instantiated and initialized 1 import arrows 2 from datetime import 3 4 K K K K K K K K K K K K KK K K K K K K K K K KK KK K K K K FF K K K K K KK KKK KKK KKK KKK gt K K K K K KKK K K K K FF K K K K K K FF K K K K K K K K K K K 5 Notice this time we just use a string as our unique ID 6 analysisEnv arrows Environment uniqueld overlayExample 7 globalSupply 5 0 VLSI TOOLS ARROWS USER MANUAL 9 amiTechnology arrows Technology vendor Ami 10 node 600 11 version a 12 environmentToUse analysisEnv 13 amiTechnology configureFromXmL 14 genericTechnology arrows Technology vendor Generic 15 node 16 version 17 environmentToUse analysisEnv 18 genericTechnology configureFromXml 19 20 In this example we will analyze 2 different sram cells and overlay their results on one plot 21 sixCell arrows Circuit technologyToUse amiTechnology 22 sixCell configureFromXml analysisEnv modelPath circuits sramCell6T xmL Line 23 is the first difference in this example where a second cell circuit is instantiated for a 7T cell The same technology is used but a local circuit XML file is used to
13. ate space 36 analysis arrows VectorField cellToAnalyze sixCell 37 bistableNodes data dataBar VLSI TOOLS ARROWS USER MANUAL 15 38 39 40 41 42 technologyToUse amiTechnology numberOfSteps 50 environmentToUse analysisEnv testbenchToUse testbench Here we will create a loop where the supple voltage is reduced in each iteration Lines 44 through 45 create an output file an write the first line a tab delimited header Inside of the loop a new supply voltage is defined in line 48 Each time through loop a DC source with the new voltage is added to the testbench The standard set of analyses are performed to measure SNM and then the DC source is removed After each iteration the SNM and current supply voltage are written to the output file for later use 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 here we are going to run a loop to determine SNM vs SupplyVoltage outputFile open analysisEnv outputPath snmVsSupply txt w outputFile writeC Vdd tSnm n for index in range 0 10 add the supply voltage with a value based on index newSupply analysisEnv globalSupply Cindex 0 02 testbench addDcVoltageSource uniqueName supply plusNode vdd minusNode value newSupply analysis runVectorFieldSim analysis parseVectorFieldSim analysis findNullclines snm repr analysis calculateSnm print Supply repr ne
14. bistable node names in the circuit netlist These must be in the inputOutput list of the subcircuit definition numberOfSteps e Description e An integer number of steps by which to quantize the state space in both dimensions environmentToUse technologyToUse testbenchToUse e Description e Environment Technology Testbench objects used in netlist generation and analysis e Description e Two lists of state space X and Y float coordinates Corresponds to the points in the quantized state space to be used during analysis Since the space is 2 dimensional the Y coordinates are repeated every numberOfSteps to ensure that these two lists are the same length CU e Description e Two lists of U and V float magnitudes These lists correspond to the coordinates in the X Y lists and represent vector components of the state space derivatives at each point For example the vector U 10 V 10 is the arrow to be plotted at the coordinated X 10 Y 10 magnitudes e Description e Alist of the float magnitudes euclidian of every vector described by the U V lists nullclineUx nullclineUy nullclineVx nullclineVy e Description e Lists of x and y coordinates of the U and V nullclines A nullcline is defined as the collec tion of points in the state space where one of the vector components are zero either the U or the V metastablePoint VES TOOLS ARROWS USER MANUAL 21 e Description e A float tuple of the metastable
15. cdsinit design 600nmAmi 2 2 cp design common ncsu cdk 1 5 1 cdssetup cds lib design 600nmAmi 3 The files we copied in step 2 rely on some environment variable to work properly Since these variables are specific to the NCSU CDK we will NOT put them in our global shell ini tialization file Instead make a local file that you will source every time you want to use the design kit For my case using CSHELL 3 1 cd design 600nmAmi 3 2 for vi use vi 600nmAmi cshrc Alternately use your favorite editor 3 3 Enter the following lines into the file changing the paths where appropriate setenv SYSTEM_CDS_LIB_DIR tools ic 5 141_usr5 tools dfII samples setenv CDSHOME tools ic 5 141_usr5 setenv CDK_DIR design common ncsu cdk 1 5 1 setenv CDS_MMSIM_DIR tools mmsim 7 0 setenv CDS_INST_DIR tools ic 5 141_usr5 VLSI TOOLS ARROWS USER MANUAL 4 Now we need to copy a few files for Arrows Take a look in the design common Arrows exampleUserDir This directory contains what a typical work directory might look like to Arrows For this setup let s just copy it all into our work directory 4 1 cp r design common Arrows exampleUserDir design 600nmAmi 4 2 cd design 600nmAmi 4 3 Edit the arrows cshrc file according to the instructions inside The most important variables to set are PATH PYTHONPATH and MMSIM_PATH Without these you will likely have the wrong version of Python running and your
16. chnologyToUse amiTechnology 34 sixCell configureFromXml CanalysisEnv modelPath circuits sramCell6T xmL 35 VLSI TOOLS ARROWS USER MANUAL Lines 36 through 54 define the test bench that will be used during the vector field analysis The testbench object is first instantiated and initialized with the generic technology line 38 A sin gle DC voltage source is then added This source is the global supply voltage and uses the value specified in the environment object In order to connect the cell properly in the testbench lines 46 through 50 specify the connections for the inputs and outputs in the cell s XML definition For the standby case the bitlines and power node are connected to the DC global supply All other inputs are grounded Lastly line 53 is included as a demonstration of how to modify the circuit s properties even when config ured using the XML file With this type of scheme one could easily run simulations where de vice size threshold mismatch etc are parameterized 36 We will analyze the 6t SRAM cell using a testbench This allows us to specify bitline wordline and supply 37 voltage values For this example we will simply create 1 DC voltage source and connect everything to it 38 sixTestbench arrows Testbench technologyToUse genericTechnology make a new testbench here 39 all we need a supply for vdd 40 sixTestbench addDcVoltageSource uniqueName Q 41 pLusNode vdd 42 m
17. define the portless structure 23 portlessCell arrows Circuit technologyToUse amiTechnology 24 portlessCell configureFromXmL circuits portlessCell xmLl notice the portless cell is defined in the user directory 25 Lines 26 through 49 setup the testbench and connect the cells inputs and outputs Notice that a second DC source is added to allow us to apply an AXS voltage to the portless cell that is less than vdd This connection is reflected in the inputsOutputs list elements 26 testbench arrows Testbench technologyToUse genericTechnology make a new testbench here 27 testbench addDcVoltageSourceCuniqueName 0 28 plusNode vdd 29 minusNode 0 30 value analysisEnv globalSupply 31 add an additional voltage source to act as the portless AXS signal 32 testbench addDcVoltageSource uniqueName 1 33 pLusNode axs 34 minusNode 0 35 value 3 0 value is lower than the global supply 36 37 Now set up the testbench connections to the cells 38 sixCell inputs0utputs leftBitline vdd vdd for standby for write 39 sixCell inputsOutputs rightBitline vdd 40 sixCell inputsQutputs wordline vdd do a read SNM this time 41 sixCell inputsQutputs power vdd 42 sixCell inputsOutputs ground 43 44 portlessCell inputs0utputs leftBitline vdd 45 portlessCell inputs0utputs rightBitline vdd 46 portlessCell inputs0utputs axsLine
18. ect for inclusion in a simula tion netlist e Arguments e format is a string describing the simulator format Default and currently only option is spectre e Return A string containing the full subcircuit definition instance uniqueName VLSI TOOLS ARROWS USER MANUAL e Description e When called returns an instance definition of the Circuit object for inclusion in a simula tion netlist e Arguments e uniqueName is a string to ensure that the instance definition is not repeated e Return A string containing the full instance definition Environment Class Relevant properties arrowsPath e Description e Astring that contains the system environment variable ARROWS_HOME e Default None uniqueld e Description e Astring name assigned to the analysis environment such that multiple or simultaneous runs of an Arrows script will not overwrite each other s data e Default None globalSupply e Description e A float specifying the supply voltage used This defines the extents of the vector field s state space x and y axis limits e Default None modelPath configPath viewPath inputPath outputPath e Description e Strings that contain absolute paths to the various directories within an Arrows installa tion e Default None Relevant methods __init_ uniqueld globalSupply inputPath outputPath e Description e Constructor method e Arguments e uniqueld is a name assigned to the analysis environ
19. figured using XML descrip tions 16 0f the process technology it s paths model templates etc Refer to config tech xml 17 For this example we are using a 0 6 micron technology from AMI in the NCSU design kit 18 amiTechnology arrows Technology vendor Ami 19 node 600 20 version a 21 environmentToUse analysisEnv 22 amiTechnology configureFromXmLO 23 we also need a generic technology which defines standard circuit elements such as voltage and current sources 24 genericTechnology arrows Technology vendor Generic 25 node 26 version 27 environmentToUse analysisEnv 28 genericTechnology configureFromXmLO 29 Lines 30 through 35 create a circuit object Our amiTechnology is linked to the circuit during initialization and then the configureFromXml method is called This method generates an in ternal representation of the circuit in this case a 6 transistor SRAM cell and will eventually allow the circuit object to output subcircuit and instance statements specific to its linked tech nology In this way technology independence is achieved and the linked technology can be changed at any point 30 The bistable circuit we will analyze in this example is a standard 6T SRAM cell 31 The cell circuit is described in the circuits sramCell6T xml file 32 We use it by creating a generic circuit object and then configuring it to be an SRAM cell 33 sixCell arrows Circuit te
20. he sixCell object for a portlessCell object in the analysis Every thing is run again for the new cell and plotted with some different colors Lines 91 through 94 output the two overlayed butterfly curves as a single PDF file 74 HE RRR RRR RRR RRR RARER Now we will run the analysis again but with the Portless cell K K K K gt K K K K K K K KHK KK K K K 75 76 analysis cellToAnalyze portlessCell 77 analysis runVectorFieldSim 78 analysis parseVectorFieldSim 79 analysis findNullclines 80 analysis calculateSnm need to do this in order to draw SNM rulers 81 and now plot the new results in a different color 82 myVectorPlot setHexColor 56CF3E 83 myVectorPlot drawNullclineUC 84 myVectorPlot drawNullclineVO 85 myVectorPlot setHexColor FCA12C 86 87 myVectorPlot drawSnmRulers C 88 89 VLSI TOOLS ARROWS USER MANUAL 14 90 Finally put everything into a PDF file in our output directory 91 print Creating PDF files 92 myVectorPlot createPdf analysisEnv outputPath overlayExample pdf 93 94 Parametric Example The parametric Arrows example demonstrates how Arrows can be used to sweep an analysis parameter and provide output as a text file instead of a PDF file The Arrows Parametric Script Lines 1 through 42 are the same as in the quick start example 1 import arrows 2 from datetime import 3 4 OK K K K K K K K K KK FK K K K K KK KK KKK KK KK KKK KK KK KK
21. ias gt specifies the alias to use in the tech xml file For example lt modelAlias gt sramPullDown lt modelAlias gt will result in device with an ami06N model based on the tech xml above lt property gt tags spec ify the properties that will be substituted into the elements in the tech xml s lt netlistFormat gt tag If a property is added that does not exist in the lt netlistFormat gt it will be ignored On the other hand if a lt netlistFormat gt element does not have a corresponding property an error will occur Finally lt expression gt tags can be used when one property is a function of another VLSI TOOLS ARROWS USER MANUAL For example a sourceArea property is generally a function of the device s width property Therefore an expression is used since the sourceArea property cannot be determine a priori Take a look at the example circuits to get an idea of what a complete circuit definition looks like Setup a directory to work from Your working directory will be the location where you run Arrows Cadence etc In this man ual we will setup the working directory to use the NCSU CDK installed above 1 Create a directory specific to the process node you want to use In my case this will be AMI Semiconductor 0 6 micron process 1 1 mkdir design 600nmAmi 2 Copy the CDS initialization and library files from the CDK common directory into your working directory 2 1 cp design common ncsu cdk 1 5 1
22. ill actually get a de vice model called ami06P The beauty of this system is that I can specify a new technology with a device template called MOSFET and a type called sramPullUlp but a completely different model alias Doing so allows my circuit to work with ANY technology The last part of the device template block is the netlistFormat tag This tag tells Arrows how to create a netlist for a particular type of simulator using this specific technology Items sur rounded by will be replaced with properties for that device instance This allows us to have simulator independence in addition to technology independence Making a circuit in XML format Circuits for analysis in Arrows are also specified in XML format This method was chosen to maintain technology independence while avoiding complex Python specification of circuit ob jects Every circuit is bracketed by lt circuit gt tags with a name property Inside of the circuit lt inputOutput gt tags are used to specify the inputs and outputs to the circuit when instantiating it in a netlist Similarly lt parameter gt tags can be added to create variables within the circuits definition The circuit structure is composed of a series of lt device gt tags Each tag contains a type defined in the tech xml file and a uniqueName to ensure that each device is unique The lt device gt tags bracket a series of lt modelAlias gt lt property gt and lt expression gt tags lt modelAl
23. ing our data 82 HH FK K gt K gt b K K K K K K OK OK K K K K K K KK KK KK KK Now Create some output to look at FK K K K K K K K K K K K K K K K K K K KK K K 83 84 Calculate the SNM as the least square fitting in the butterfly curve 85 print SNM Vectors repr analysis calculateSnm 86 87 To plot some state space curves in a PDF or EPS file we need a VectorPlot object 88 myVectorPlot arrows VectorPlot analysis analysisEnv 89 90 Uncomment the next line to plot the actualy vector field 91 myVectorPlot drawNormalizedVectorField 92 93 Set the color and plot the nullclines butterfly curve 94 myVectorPlot setHexColor 3E6BCE 95 myVectorPlot drawNullclineUC 96 myVectorPlot drawNullclineVC 97 Set the color and plot the Least square box used to calculate SNM 98 myVectorPlot setHexColor FCA12C 99 myVectorPlot drawSnmRulers 100 101 Set the color and draw the metastable point and separatrix 102 myVectorPlot setHexColor 2BFC32 103 myVectorPlot drawMetastablePoint 104 myVectorPlot drawSeparatrix 105 106 Finally put everything into a PDF file in our output directory 107 print Creating PDF files 108 myVectorPlot createPdf analysisEnv outputPath field analysisEnv uniqueld pdf Overlay Example The Arrows overlay example demonstrates how Arrows can analyze two different cell types under the same technology testbench and environment The butterfly curves
24. inusNode 0 43 value analysisEnv globalSupply 44 45 Now set up the testbench connections to the cells 46 sixCell inputsOutputs leftBitline vdd vdd for standby for write 47 sixCell inputsOutputs rightBitline vdd 48 sixCell inputsOutputs wordline 0 0 means standby mode set this to vdd for either read or write 49 sixCell inputsQutputs power vdd 50 sixCell inputsOutputs ground 0 SL 52 if we want to modify some properties of the circuit we can do it here to override the XML configuration 53 sixCell devices leftPullDown length 1u 54 Lines 55 through 72 run the dynamical analysis vector field analysis The analysis object is in stantiated and initialized using our 6T circuit the AMI technology object and an analysis envi ronment In addition the names of the bistable nodes are given as a string list These two nodes define the state space of the analysis Lastly a numberOfSteps is given which controls how many divisions the state space is quantized into for each dimension After the vectorField simulation is actually executed in line 68 a separate method in line 72 is invoked to parse and clean up the intermediate simulation files If cleanUpWhenDone is set to zero all intermediate files will be left in the input directory for debugging purposes VLSI TOOLS ARROWS USER MANUAL 10 55 The actual analysis is a VectorField analysis object 56 Ini
25. ment such that multiple or simulta neous runs of an Arrows script will not overwrite each other s data e globalSupply is a float specifying the supply voltage used This defines the extents of the vector field s state space x and y axis limits e inputPath specifies a directory to use for input to Arrows if the default userDirectory input is unacceptable keep in mind that when Arrows generates a netlist for simula tion it will put that netlist into this input path e outputPath specifies a directory to use for Arrows output if the default userDirectory input is unacceptable e Return None VLSI TOOLS ARROWS USER MANUAL 18 Technology Class Relevant properties vendor node version e Description e Strings from a tech xml file corresponding to the unique properties of a technology e Default None modelTypes e Description e Adictionary whose keys are read from the tech xml file for each type of model and whose keys are the string definitions of those types for a netlist file e Default None modelPaths e Description e Alist of all the paths required for inclusion in a simulation of a particular technology e Default None devices e Description e Adictionary of device types Each key points to an internally defined device class that contains the properties for model aliasing and netlist formatting e Default None Relevant methods _ init_ vendor node version environmentToUse e Description e
26. methods are called internally e Return None addDcVoltageSource uniqueName plusNode minusNode value e Description e Adds an instance of a DC voltage source to the current testbench netlist e Arguments e uniqueName is the string instance name used in the netlist e plusNode minusNode are the string connections for the voltage source i e vdd 0 e value is the float value for the DC voltage e Return None write ToFile fileHandle e Description e Adds the testbench netslist to a file via it s opened file handle e Arguments e fileHandle is a handle to a ascii text file created using the open method in Python e Return None remove uniqueName e Description e Removes an element from the testbench netlist e Arguments e uniqueName is the name of the element to be removed from the internally maintained list of testbench devices e Return None clear e Description e Clear all elements in the internal list of testbnech elements e Arguments None VLSI TOOLS ARROWS USER MANUAL 20 e Return None VectorField Class This class is the main workhorse of the Arrows framework for vector field analysis Ithandles gen eration of simulation netlists simulation execution post processing and data analysis Relevant properties cellToAnalyze e Description e ACircuit object representing a bistable system to analyze bistableNodes e Description e Alist of two strings corresponding to the
27. ommon ncsu cdk 1 5 1 models spectre standalone ami06N m lt modelPath gt After the model paths the technology must contain a list of device templates The de vice templates tell Arrows how to write instances of a device for a particular technology The best way to explain the device template format is with an example lt deviceTemplate name MOSFET gt lt modelAlias model ami06N gt nmos lt modelAlias gt lt modelAlias model ami06P gt pmos lt modelAlias gt lt modelAlias model ami06N gt sramPullDown lt modelAlias gt lt modelAlias model ami06P gt sramPullUp lt modelAlias gt lt modelAlias model ami06N gt sramPassGate lt modelAlias gt lt netlistFormat simulator spectre gt VLSI TOOLS ARROWS USER MANUAL M uniqueName drain gate source body model w width I length as ami600areaSourceDiff usion ad ami600areaDrainDiffusion ps ami600perimeterSourceDiffusion pd ami600perimeterDrainDiffusion lt netlistFormat gt lt deviceTemplate gt First the device template is given a name In this case MOSFET is used Any time an Arrows script is using this technology it can instantiate a device called MOSFET Clearly no simulator will know what a MOSFET is therefore the next section of the device template includes model aliases Model aliases map a device type to an actual model name So if an Arrows script uses a device called MOSFET and it s type is sramPullUp the simulation netlist w
28. scripts will not know where to find Arrows More importantly you will not be able to run any of the simu lations required without command line access to Spectre VLSI TOOLS ARROWS USER MANUAL Quick Start Example The included quick start example demonstrates how to setup and run a basic vector field analy sis of a6T SRAM cell in the AMI 600nm technology The vector field is generated and from it butterfly curves are generated and a static noise margin measurement is taken The state space with the superimposed butterfly curves is plotted in a PDF file for viewing The Arrows Quick Start Script The quick start script is located in the exampleUserDir directory It gives a step by step example of using Arrows to do some basic analysis To run the script 1 cd design 600nmAmi 2 edit quickStart py so that the paths are real For example replace design 600nmAmi with an actual path such as users me home design 600nmAmi 3 make sure the paths in arrows cshrc are properly configured 4 source arrows cshrc 5 python quickStart py Let s go over the script piece by piece to learn the basics of Arrows Lines 1 through 29 setup the Arrows environment and technology objects The environment object is instantiated in like 12 and initialized with a global supply voltage of 5 0 volts and a unique name that is a function of today s date The unique name prevents overwriting of intermediate data when you run multi
29. t is stored internally as a property traceSeparatrix e Description e Traces the separatrix boundary between the two stable manifolds inside of the vector field using an interpolation algorithm Assumes that the metstable point has already been found using the findMetastablePoint method Separatrix points are stored inter nally as a property and may not coincide with points in the X Y state space lists e Arguments None e Return None measureSeparatrixAreas e Description e Measures the area of the state space on either side of the separatrix Since the separa trix is not always a 45 degree line bisecting the state space this is a good measure of mismatch impose skew in the bistable circuit e Arguments None e Return A tuple of ratioA ratioB where the sum of the two ratios is 1 and each represents a fraction of the total state space area UVatxY x y e Description e Auseful utility method to provide a U V value for any point x y using two sided vector interpolation e Arguments x y are floating point coordinates for any value within the state space bounda ries e Return A tuple U V of the interpolated vector components stablePointClosestToSeparatrix VLSI TOOLS ARROWS USER MANUAL 23 e Description e Calculates which stable point is closest to the separatrix e Arguments None e Return A triplet distance stablePoint and separatrixPoint distance ToSeparatrix pointToMeasureFrom
30. table node names in the circuit to analyze e numberOfSteps is the quantization factor of the state space e Return None runVectorFieldSim e Description e Executes a variety of internal methods to create the simulation netlists and run the simulation e Arguments e None e Return None parseVectorFieldSim outputFile cleanUpWhenDone e Description e Parses the simulation output to determine vectors from the operating points and nodal capacitance VLSI TOOLS ARROWS USER MANUAL e Arguments e outputFile is an optional file path string where X Y U V data will be dumped after parsing e cleanUpWhenDone is an optional boolean defaulting to true If false all intermediate simulation files will be left in the output directory e Return None findNullclines e Description e Searched the vector field for null cline components and stores the result internally e Arguments None e Return None calculateSnm e Description e Calculates the noise margins of the system by rotating the nullclines about the 45 degree line resampling them and then subtracting them The result is stored internally e Arguments None e Return The minimum float value of the two measured SNMs is returned findMetastablePoint e Description e Calculates the metastable point by intersecting the nullclines Assumes that the null clines have already been determined using the findNullClines method e Arguments None e Return None resul
31. tialize this object using our SRAM object technology etc 57 The bistableNodes are a list of the 2 nodes considered in the state space 58 The numberOfSteps is the quantization parameter for the state space 59 analysis arrows VectorField cellToAnalyze sixCell 60 bistableNodes data dataBar 61 technologyToUse amiTechnology 62 numberOfSteps 50 63 environmentToUse analysisEnv 64 testbenchToUse sixTestbench 65 66 Run the actual sim 67 make sure that the cshrc is sourced beforehand or else spectre will fail 68 analysis runVectorFieldSim 69 70 Parse the output from the sim and populate our analysis object with the results 71 cleanUpWhenDone determines whether or not we leave the intermediate files in the input output directories 72 analysis parseVectorFieldSim cleanUpWhenDone 1 Lines 73 through 81 execute some analyses on the internal vector field data The nullclines but terfly curves are extracted from the vector field in line 74 Based on the nullcline intersection the metastable point is determined in line 77 Once that is found the separatrix could be traced as in line 80 This is commented out for our example to save time Notice that these commands are interdependent one cannot trace the separatrix without first finding the metastable point and one cannot find this point without first tracing the nullclines 73 Find the null clines corresponds to the DC transfer c
32. urves of a standard buterfly simula tion 74 analysis findNullclines 75 Find the metastable point by intersecting the nullClines 76 Can t do this until the nullClines have been located 77 analysis findMetastablePoint 78 79 Trace the metastable point along the separatrix back to the boundaraies 80 analysis traceSeparatrix 81 Lines 82 through 108 encapsulate the visualization portion of the quick start script First the SNM are calculated using the smallest square method in line 85 It is important to note that printing the SNM value to the terminal is not the only function of this method call Line 99 will not be able to properly draw the SNM boxes if it is not first calculated A VectorPlot object is instantiated and initialized in line 88 The analysis and its environment are passed in during this process This object effectively creates the two dimensional state space plot internally for eventual output as a PDF or EPS file Line 91 is commented out but could be used to plot all of the vectors in the field Lines 94 through 96 set the drawing color and plot the nullclines For each dynamical analysis there are two nullclines U and V Plotting both is VLSI TOOLS ARROWS USER MANUAL 11 equivalent to plotting the cell s butterfly curves Lines 102 through 104 are used to plot the metastable point and the separatrix if it was traced Lastly line 108 outputs a PDF file in the output directory contain
33. wSupply SNM repr snm n outputFile writeCrepr newSupply t repr snm n remove the supply DC source since we add one at the top of the loop testbench remove supply outputFile close VLSI TOOLS ARROWS USER MANUAL 16 Class Reference Circuit Class Relevant properties inputsOutputs e Description e Adictionary whose keys represent inputs and output defined in the subcircuit and whose values represent their connection in the instance definition e Default Empty devices e Description e Adictionary whose keys represent device names specified in the circuit XML and whose values are a dictionary of properties for that device e Default Empty parameters e Description e Adictionary whose keys represent circuit parameters specified in the circuit XML and whose values are added to the instance definition e Default Empty Relevant methods _init_ environmentToUse technologyToUse e Description e Constructor method e Arguments e environmentToUse is an object of type Environment e technologyToUse is an object of type Technology e Return None configureFromXml circuitXmlFilePath e Description e When called populates the circuit object with a definition from the associated XML file e Arguments e circuitXmlFilePath is an absolute string path to a XML circuit description e Return None subCircuit format e Description e When called creates a subcircuit definition of the Circuit obj
34. you want to combine their data Used in conjunction with the getGraph method e Arguments e graphToUse is a PyX graph object e Return None setColor red green blue e Description e Utility method used to set the internal drawing color Use this method before executing a plot command of any kind to control the result e Arguments e red green blue are floats between 0 and 1 representing the RGB composition of the color e Return None setHexColor hexColor e Description e Utility method used to set the internal drawing color Use this method before executing a plot command of any kind to control the result e Arguments e hexColor is a string of the format A2C80B where every pair of hex characters repre sents an 8 bit value for R G and B components of the color e Return None VLSI TOOLS ARROWS USER MANUAL drawVectorField e Description e Adds the U V arrows to the vector field plot These arrows can be very lage and may re sult in unreadable outputs Refer to the drawNormalizedVectorField method below e Arguments None e Return None drawNormalizedVectorField normScale filter e Description e Same as drawVectorField but the arrows lengths are normalized to the longest arrow in the field e Arguments e normScale is a float factor multiplied by the largest normalized vector length e filter is a float which drops vectors less than this length from the field drawing e Return None
35. z VLSI TOOLS ARROWS USER MANUAL Configuring tech xml To isolate technology specific configuration from analysis and circuit design Arrows makes use of a tech xml file A global version of this file lives in design common Arrows config A sys tem administrator could setup a tech xml for all of the globally installed technologies A user may also have their own tech xml located anywhere the wish Upon creating a technology ob ject in an Arrows script you simply choose whether to use the global tech xml default or the local copy A tech xml file contains several important elements Each technology you want to give Arrows access to is bracketed by lt technology gt tags The tags have a property called name which is a concatenation of the Vendor the Node and the Version For example if I have a technology available to me from TSMC that is a 45nm node and version 1 2 I would add to my tech xml lt technology name TSMC45nm1 2 gt lt technology gt Inside of these technology tags two types of elements need to be added The first is a model path Each model path tag corresponds to a path that is included at the top of any simulation using this technology You can have as many model path tags as you d like and each one can contain an optional paramter called section For example lt modelPath section tt gt common ncsu cdk 1 5 1 models spectre standalone ami06P m lt modelPath gt lt modelPath gt c
Download Pdf Manuals
Related Search