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@@ -1,192 +1,110 @@ -\chapter{NGHDL: Mixed Signal Simulation} +\chapter{SKY130 Interface with eSim} \label{chap9} \thispagestyle{empty} +SkyWater Open Source PDK provides a completely open source Process Design Kit for the 130nm Technology Node. SKY130 PDK provides a lot many features and components to its library. The MPW Shuttle is a free chip fabrication shuttle program sponsored by the Google where the designs made using the SKY130 PDK may be fabricated at no cost. -NGHDL feature facilitates creation of user-defined models for mixed-signal circuit simulation in eSim. By interfacing GHDL and Ngspice, we achieve mixed-signal simulation. Digital models are simulated using GHDL and XSPICE engine of Ngspice. \\ +eSim being an Open Source EDA Tool has being interfaced with the SKY130 PDK. eSim-2.3 and above is supporting the PDK. Currently only the primitive libraries(sky130\_fd\_pr) are supported, however, the symbols for other libraries are also loaded in eSim, so even the other ones can be interfaced with eSim with few manual changes. +The various steps involved in simulating a circuit schematic in eSim interfaced with SKY130 are explained in the sections below: +\section {Schematic Creation} +\begin{itemize} -%To access NGHDL click on the NGHDL button on the left pane of window as shown in figure \figref{screen3}: -%\pagebreak +\item The steps of opening the Eeschema and editing are same as mentioned in the previous Chapters. +\item To create a Schematic in eSim for SKY130, one needs to use the SKY130 components. +\item The SKY130 components are available in the \textbf{eSim\_SKY130} library. It can be chosen by clicking on the \textbf{Place Component} button on the Right Toolbar and searching for the same in the \textbf{Choose Component} Dialog Box. -\section{Introduction} - -Ngspice supports mixed-signal simulation, i.e. it can simulate both digital and analog component. It defines a \texttt{model} which has the functionality of the circuit component, which can be used in the netlist. -For example you can create an \texttt{adder} model in Ngspice and use it in any circuit netlist of Ngspice. \\ - -However, it is not feasible to define complex digital models without a complete understanding of Ngspice and XSPICE architectures and is a time-consuming process. Also, most of the users are familiar with GHDL and can write the models using VHDL code with ease. -Hence, NGHDL provides an interface to write VHDL code for a digital model and install it as model in Ngspice. So whenever Ngspice looks for that model, it will actually interface with VHDL code to get the result. \\ - -\begin{figure}[!htp] +\begin{figure}[H] \centering -\includegraphics[width = 13cm, height = 7cm]{./NGHDL/NGHDL_Overview.png} -\caption{Overview of NGHDL} -\label{overview} +\includegraphics[ height = 5cm]{./SKY130/SKY130libraries.png} +\caption{eSim\_SKY130 Libraries} +\label{eSimSKY130 Libraries} \end{figure} -%description of Overview: -\figref{overview} shows the overview of NGHDL indicating its architecture at the abstract level. The values for the digital models present in the netlist are fetched from the GHDL side of the interface whereas the values of the analog part are fetched from Ngspice's spice3f5 engine. Digital and Analog components in \figref{overview} are connected to each other with the help of the hybrid ADC and DAC models provided by Ngspice. This helps in the signal level switching when simulation is performed. As analog signals are in continuous time domain and Digital signals are in discrete time domain, hybrid components help bridge the gap. More information on the parameters of ADC and DAC present in Appendix : D. - -\pagebreak - -\section{Digital Model creation using NGHDL} +\item One may even chose the predefined IPs made in SKY130 available in eSim. These IPs are available in the \textbf{eSim\_SKY130\_Subckts} library. It can be chosen by clicking on the \textbf{Place Component} button on the right Toolbar and searching for the same. -%Description of User Flow of NGHDL - -\begin{figure}[!htp] +\begin{figure}[H] \centering -\includegraphics[width = 13cm, height = 7cm]{./NGHDL/NGHDL_Flow.png} -\caption{User Flow for NGHDL} -\label{user_flow} +\includegraphics[ height = 5cm]{./SKY130/SKY130subcktlibraries.png} +\caption{eSim\_SKY130\_Subckts IP Libraries} +\label{eSimSKY130Subckts IP Libraries} \end{figure} - -\noindent \textbf{The steps to create digital models are given below}: - -\begin{enumerate} -\item Click on NGHDL button on left side pane of main window, the Ngspice Digital Model Creator window will appear as shown in \figref{screen3} - \begin{figure}[!htp] - \centering - \includegraphics[height=10cm, width =\lgfig]{./NGHDL/screen3.png} - \caption{NGHDL interface} - \label{screen3} - \end{figure} - - -\item Now browse and locate the VHDL file to upload. Select the VHDL file and click on the Upload button. This process will create Ngspice model and corresponding component drawing inside the KiCad library (eSim\_Nghdl.lib) of the VHDL block to be used in mixed-signal simulations. An acknowledgement message will appear upon sucessful processing of the VHDL code as shown in \figref{upload}. \\ - - \begin{figure}[!htp] - \centering - \includegraphics[width =\smfig]{./NGHDL/screen4.png} - \caption{Uploading of digital model} - \label{upload} - \end{figure} - -Note : \texttt{"Add files"} option allow you to use a smaller entity / subpart / submodule to support the main VHDL file. That is, a digital model will be generated corresponding to that file that has been browsed. The file that has been \texttt{"added"} to Nghdl upload window will only be placed along with the model under model’s DUTghdl folder to support the model. - -Hence, \texttt{"browsing"} one file and \texttt{"adding"} several files won’t create that many number of models, but only one model will be created corresponding to the browsed file. -\end{enumerate} - -\section{Schematic Creation} -Steps for schematic creation are as follows: -\begin{enumerate} -\item Click on New Project icon to create a new project as shown in \figref{screen1}, be careful of the naming conventions. -%To access nghdl click on the NGHDL button on the left pane of window as shown in figure \figref{screen3}: - -\begin{figure}[!htp] +\item \textbf{It is important to choose the SKY130mode from the eSim\_SKY130 to switch eSim into the SKY130 mode.} +\begin{figure}[H] \centering -\includegraphics[width = 13cm, height = 7cm]{./NGHDL/screen1.png} -\caption{Creation of a new project} -\label{screen1} +\includegraphics[ height = 5cm]{./SKY130/SKY130Mode.png} +\caption{SKY130Mode} +\label{SKY130Mode} \end{figure} +\item Let us look into the CMOS Inverter as an example. Here is an example schematic of a CMOS Inverter made from the SKY130 components: +\begin{figure}[H] +\centering +\includegraphics[ height = 8cm]{./SKY130/SKY130InverterSchematic.png} +\caption{CMOS Inverter Schematic using SKY130 components} +\label{eSimSKY130Subckts IP Libraries} +\end{figure} +\item Note: While using SKY130mode in eSim, use the components of designators `sc', `u', `x', `v', `i', `a'. This is to ensure that other necessary technology node does not get included while in the SKY130 mode. +\item Annotate the schematic and generate the netlist. Please follow the steps given in previous chapters to do the same. -\item After successful upload of the model using the VHDL code, you can create the schematic of your design by clicking on \texttt{Open Schematic} button on the left pane of the eSim window. Then go to \texttt{Preferences} option on top of the schematic editor window and click on \texttt{Component Libraries} to add the library eSim\_Nghdl.lib in KiCad. Following window will appear as shown in \figref{screen6}, where you will have to click on \textit {Add} button and select the \texttt{eSim\_Nghdl} library. Refer \figref{screen6} and \figref{screen7}. %%last sentence may not be required - - \begin{figure}[!htp] - \centering - \includegraphics[width =\smfig]{./NGHDL/screen6.png} - \caption{Adding the digital model library in KiCad} - \label{screen6} - \end{figure} - - - \begin{figure}[!htp] - \centering - \includegraphics[width =\smfig]{./NGHDL/screen7.png} - \caption{Selection of library} %%this may not be required either - \label{screen7} - \end{figure} - - - - \pagebreak - \item Next step is to locate the component in \texttt{eSim\_Nghdl} library as shown in \figref{screen9} and place it on the schematic editor as shown in \figref{screen10}. - \begin{figure}[!htp] - \centering - \includegraphics[width =\smfig]{./NGHDL/screen9.png} %%Change this image - \caption{Locating the component in library} - \label{screen9} - \end{figure} - - - \begin{figure}[!htp] - \centering - \includegraphics[width =\smfig]{./NGHDL/screen10.png} - \caption{Placement of component on editor} - \label{screen10} - \end{figure} -\pagebreak - -\item Now create the schematic as shown in \figref{screen14}, annotate, perform ERC, create the netlist and save the schematic by following the steps given in Chapter 5. -\begin{figure}[!htp] - \centering - \includegraphics[width =\hgfig]{./NGHDL/screen14.png} - \caption{Example of an AND gate characteristics circuit} - \label{screen14} - \end{figure} - -\item After creating the schematic, click on \texttt{KiCad-to-Ngspice converter} and select the type of analysis as transient as shown in \figref{screen15} and set the start, step and stop time as shown in \figref{screen16} - \begin{figure}[!htp] - \centering - \includegraphics[width =\hgfig]{./NGHDL/screen15.png} - \caption{Analysis Part I} - \label{screen15} - \end{figure} - \begin{figure}[!htp] - \centering - \includegraphics[width =\hgfig]{./NGHDL/screen16.png} - \caption{Analysis Part II} - \label{screen16} - \end{figure} -\pagebreak - -\item Now click on \texttt{Source Details} and enter the values for Source v1 and source v2 as shown in figure \figref{val1} and \figref{val2} -\begin{figure}[!htp] - \centering - \includegraphics[width =\hgfig]{./NGHDL/val1.png} - \caption{Value of Source v1} - \label{val1} - \end{figure} - \begin{figure}[!htp] - \centering - \includegraphics[width =\hgfig]{./NGHDL/val2.png} - \caption{Value of Source v2} - \label{val2} - \end{figure} +\end{itemize} -\item Now select the option \texttt{Ngspice Model}, window as shown in \figref{screen17} will appear. The values of the parameters listed can be changed per user's requirement. If you have used any semicnductor devices and Subcircuits in your design, then please specify the Spice models and subcircuits in the \texttt{Device Modeling} and \texttt{Subcircuits} tabs of the \texttt{KiCad-to-Ngspice converter} window. After that click on \texttt{Convert} button. This step will create the simulation compatible netlist. - \begin{figure}[!htp] - \centering - \includegraphics[width =\hgfig]{./NGHDL/screen17.png} %Change the figure - \caption{Model Parameters} - \label{screen17} - \end{figure} -\item Now click on \texttt{Simulation} button, it will display the following windows as shown in \figref{screen19}. This is the Ngspice terminal and Python plot window. -\begin{figure}[!htp] - \centering - \includegraphics[width =\hgfig]{./NGHDL/screen19.png} - \caption{Simulation window} - \label{screen19} - \end{figure} -\pagebreak -\item Now select the required nodes and click on \texttt {Plot} button. You can see the plots of input source v1, input source v2 and output as shown in \figref{plotv1}, \figref{plotv2}, and \figref{plotout} respectively. -\begin{figure}[!htp] - \centering - \includegraphics[width =\lgfig]{./NGHDL/plotv1.png} - \caption{Plot of Source V1} - \label{plotv1} - \end{figure} -\begin{figure}[!htp] - \centering - \includegraphics[width =\lgfig]{./NGHDL/plotv2.png} - \caption{Plot of source V2} - \label{plotv2} - \end{figure} -\begin{figure}[!htp] - \centering - \includegraphics[width =\lgfig]{./NGHDL/plotout.png} - \caption{Plot of output} - \label{plotout} - \end{figure} + \section {KiCad to Ngspice Conversion} - \pagebreak +\begin{itemize} +\item Click on the \textbf{Convert KiCad to Ngspice Button} available in the Left Toolbar of the eSim Main Window. +\item Add all the simulation parameters and the Source details in the \textbf{Analysis Tab} and the \textbf{Source Details Tab}. Refer previous chapters of this manual to do the same. +\item Click on the \textbf{Device Modeling Tab}. +\item The options for the SKY130 PDK are involved in the \textbf{Device Model Tab}. The Device Model Tab for the CMOS Inverter project is shown in Fig. \ref{DeviceModelTab}. +\begin{figure}[H] +\centering +\includegraphics[ height = 5cm]{./SKY130/DeviceModelTab.png} +\caption{Device Model Tab of CMOS Inverter using SKY130} +\label{DeviceModelTab} +\end{figure} +\item The user may select the \textbf{Add Default Path} option to add the Default Path of the PDK installed along with eSim. Note that only primitive libraries(sky130\_fd\_pr) are present here. +\item In order to select path to any other SKY130 PDK, the user may add the path by clicking on the \textbf{Add} button. +\item The user can add the SPICE model parameters for the components in the text-box provided. +\item If a SKY130 Subcircuit IP is added in the circuit. Then Click on the \textbf{Subcircuits Tab}. For Example, refer Fig.\ref{Subcircuits Tab}. +\begin{figure}[H] +\centering +\includegraphics[ height = 7cm]{./SKY130/Subcircuits.png} +\caption{Subcircuits Tab} +\label{Subcircuits Tab} +\end{figure} +\item Click on the \textbf{Add} button. +\item Browse to the SKY130 folder and Click on it. Click the IP Subcircuit to be included. Click on the Open Button on the top right corner. +\begin{figure}[H] +\centering +\includegraphics[ height = 6cm]{./SKY130/SubcircuitsPath.png} +\caption{Adding path to the Subcircuit} +\label{SubcircuitsPath} +\end{figure} +\item The Subcircuit chosen gets added. Refer Fig. \ref{SubcircuitsAdded}. +\begin{figure}[H] +\centering +\includegraphics[ height = 6cm]{./SKY130/Subcircuitsadded.png} +\caption{Subcircuit Added} +\label{SubcircuitsAdded} +\end{figure} +\item Click on the \textbf{Convert} button. +\item A Dialog Box \textbf{The KiCad to Ngspice conversion completed successfully!} appears on the screen showing that the conversion is successful. +\item If something needs to be added manually, Click on the \textbf{ \textit{Project\_Name}.cir.out} file in the left \textbf{Project Panel} and the file can be edited manually. Refer Fig. \ref{netlist} as an example. +\begin{figure}[H] +\centering +\includegraphics[ height = 6cm]{./SKY130/netlist.png} +\caption{Manually Editing the Netlist} +\label{netlist} +\end{figure} +\end{itemize} -\end{enumerate}
\ No newline at end of file +\section {Run Simulation} +\begin{itemize} +\item To run the simulation, Click on the \textbf{Simulate} button on the Left Toolbar. +\item Refer Fig. \ref{Simulation Results} for the simulation results of the CMOS Inverter using SKY130. +\begin{figure}[H] +\centering +\includegraphics[ height = 6cm]{./SKY130/Simulation.png} +\caption{Simulation Results of CMOS Inverter using SKY130} +\label{Simulation Results} +\end{figure} +\end{itemize} +In this way, the SKY130 PDK has been interfaced with eSim. |