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By Neel Shah

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+1.  When `nghdl` button clicked in `eSim` it calls the `ngspice_ghdl.py` from `nghdl` installed directory
+- `ngspice_ghdl.py` defines the UI for nghdl, and the functionality of each button
+- When `Upload` clicked, it calls `uploadModle` function from `ngspice_ghdl.py`
+- Similarly functions called on each button click defined
+- `uploadModle` inturn calls these 5 functions sequentially =>
+- - createModelDirectory()
+- - addingModelInModpath()
+- - createModelFiles()
+- - runMake()
+- - runMakeInstall()
+
+2. `createModelDirectory()`
+- Create directory for the specified file name at `~/ngspice-nghdl/src/xspice/icm/ghdl/`
+- The location where the directory is created in mentioned at `~/.nghdl/config.ini`, this config file is inside a hidden folder `.ngdhl`, created when nghdl is installed
+- If a folder of the same name exists, it asks to overwrite, then removes earlier folder, and writes new one
+
+3. `addingModelInModpath()`
+- This adds the name of the new model created to `modpath.lst` file
+- `modpath.lst` is located at `~/ngspice-nghdl/src/xspice/icm/ghdl`, this should contain name of all the models that the folder has
+- Similarly you can look at `~/ngspice-nghdl/src/xspice/icm/digital` which also contains a `modpath.list` for all the models in that folder
+- This `modpath.lst` is used in the `GNUMakefile` at `~/ngspice-nghdl/release/src/xspice/icm`
+- This file used to keep a track of all components created
+- If model already there it isn't added to the list
+
+4. `createModelFiles()`
+- Calls `model_generation.py` at the installed nghdl location under `src/model_generation.py`
+- Moves the generated `cfunc.mode` and `ifspec.ifs` files to `~/ngspice-nghdl/src/xspice/icm/ghdl/modelName`
+- Creates  `DUTghdl` folder at `~/ngspice-nghdl/src/xspice/icm/ghdl/modelName`
+- Move `compile.sh`,`uthash.sh`,`ghdlserver.c`,`ghdlserver.h`,`Utility_Package.vhdl`,`Vhpi_Package.vhdl` to the `DUTghdl` folder
+- Copy `modelName.vhdl` file from source location to `DUTghdl` folder
+- Rum `compile.sh` which generates the object file for `ghdlserver.c`
+- Give permission to `start_server.sh` and `sock_pkg_create.sh` to execute _chod a+x_
+- Finally remove `compile.sh` and `ghdlserver.c`
+
+5. `model_generation.py`
+- Creates the following files =>
+- - `connection_info.txt`
+- - `cfunc.mod`
+- - `ifspec.ifs`
+- - `modelName_tb.vhdl` => testbench file for the model
+- - `start_server.sh`
+- - `sock_pkg_create.sh`
+- The above files can be found either at `~/ngspice-nghdl/src/xspice/icm/ghdl/modelName` or `DUTghdl` folder inside it
+
+6. `runMake()`
+- Runs the `Makefile` at `~/ngspice-nghdl/release`
+- Executing by running `make` command
+
+7. `runMakeInstall()`
+- Executes `make install`
+- Finally calls `createSchematicLib()`
+
+8. `createSchematicLib()`
+- Connects with `createKicadLibrary.py` file at `~/nghdl/src` 
+- Generates the `lib` file for the model, to be used by `KiCad`
+- This is generated from a template stored at  `Appconfig.py`
+- The generated `lib` is stored at `~/eSim_kicad.lib`
+- Also creates `xml` file for the model, which is stored at eSim under `eSimLoc/src/modelParamXML/Nghdl
+
+<br/>
+
+Finally all the relevant files are generated, now while executing ngspice, we need to make sure to run the ngspice, which is located at -
+- `~/ngspice-nghdl/install_dir/bin/ngspice` this has the binary for the ngspice,
+- And also the script at `~/ngspice-nghdl/install_dir/share/ngspice/scripts/spinit`
+= ` spinit` has the line `codemodel ...` mentioning a `cm` file to execute at runtime
+- This has mention of `ghdl.cm` which makes sure that our `cfunc.c` file is executed at runtime
+- You can see the `ghdl.cm` file is located at `~/ngspice-nghdl/release/src/xspice/icm/ghdl`
+- Also the `cfunc.c` files, located at `~/ngspice-nghdl/release/src/xspice/icm/ghdl/modelName`
+- These have mention of the `start_server.sh` file at `DUTghdl`, hence server is started and values passed as well
+- Also you can look at `~/ngspice-nghdl/release/src/xspice/icm/digital` it has `digital.cm` and the folders inside have `cfunc.c`
+- Also has `ifspec.c` which defines the interface
+
+<br/>
+
+- Note that, if you have ngspice currently installed remove it and genearate a softlink or command for the ngspice installed at -
+`~/ngspice-nghdl/install_dir/bin/ngspice`
+- `whereis ngspice`, run this to get the location from where `ngspice` is being executed currently
+<br/>
+
+- To generate softlink refer - [Creating softlink](https://askubuntu.com/questions/56339/how-to-create-a-soft-or-symbolic-link)i
+- Exeecute `ln -s ~/ngspice-nghdl/install_dir/bin/ngspice /usr/bin/ngspice`
+
+
+<br/>
+
+- Also the installation script doesn't install ghdl, you will have to do it manually, either through a `.deb` package or build it from [source](https://github.com/ghdl/ghdl)
+- Note that since we are using socket programming here, we require either the `llvm` architecture or `gcc`. Using `mcode` backend won't work here
+
+<br/>
+
+- To install ghdl from source, [this](https://github.com/ghdl/ghdl/issues/550) Github issue might be helpfu, the steps are -
+- - `sudo ./configure --with-llvm-config`
+- - sudo make
+- - sudo make install
+- Check [this](https://github.com/ghdl/ghdl/issues/166) Github issue for those building from `.deb` package
+- To check current version and architecure of ghdl use -
+- - `ghdl --version` command, it should have `llvm` code generator or `gcc`
+<br/>
+
+- Also once ghdl is installed, to check syntax of your vhdl files use -
+`ghdl -s <vhdl file location>`
+- Note that we need `std_vector_logic` as our ports here