michea

Extending the Power of IC-CAP Software with Python—PyVISA Instrument Control

Blog Post created by michea on May 31, 2017

Many of you already know that Keysight's IC-CAP software provides an open flexible architecture that supports many industry standard and proprietary models. It also provides drivers for a range of popular test instruments required to make characterization measurements for extracting device model parameters and performing optimizations. But did you know that you can customize your IC-CAP environment to tackle your own measurement challenges?

 

This might be very welcome news if you are working with cutting-edge devices and need more than the capabilities already provided by IC-CAP. For many of these devices, skirting the limits of today’s technology often means that the measurement capabilities required are a moving target. And that can be a costly and time-consuming proposition if you have to buy and integrate new software tools every time you need new functionality. Your ability to automate these advanced measurements may even mean the difference between the success or failure of your project.

 

What if you need to implement your own behavioral model in Verilog-A along with custom parameter extraction routines? What if you want to create new measurement routines for controlling an arbitrary waveform generator? What if you want to add a time-domain measurement capability using an oscilloscope to capture your device’s fast pulse response? 

 

I faced such a scenario in my work at nSpace Labs, where I'm developing custom models for memristors and adding advanced measurement routines using the Keysight B1500A Semiconductor Device Analyzer. This analyzer is configured with multiple high-resolution SMUs (Source Measurement Units) and an integrated B1530A WGFMU (Waveform Generator/Fast Measurement Unit) to apply pulsed and arbitrary waveforms to the memristor’s electrodes, while simultaneously performing Fast-IV measurements. I needed to communicate with the WGFMU via GPIB using a Keysight provided software library and API for the WGFMU, something that is not currently supported by IC-CAP.

 

To take advantage of the WGFMU capabilities, I decided to use the Python programming language, included in all recent versions of IC-CAP, and PyVISA—a Python module that enables control of all kinds of measurement devices independent of the interface (e.g., GPIB, RS-232, USB or LAN). Utilizing IC-CAP's integrated Python environment, I was able to extend the software’s built-in measurement capabilities by integrating the third-party libraries and Python modules I needed for my application. This enabled me to programmatically generate the waveforms using Python, and then send the appropriate commands to the WGFMU for pulsing and simultaneously making Fast-IV measurements on my devices.

 

It took some effort, but I figured out how to install the WGFMU library and PyVISA package within a virtual Python environment for use with Keysight IC-CAP 2016. Now, I'd like to share with you the procedure for using some free Python packages and modules to extend the capabilities of IC-CAP. Using the WGFMU measurement routines that I have developed in Python, I am now able to extract and optimize parameters for my memristor model and have the ability to more accurately simulate the incremental conductance change of the memristor when a series of pulses are applied. Having more accurate models and the accompanying time-based measurement data provide me with a better understanding of the performance of the memristor-based circuits that I am designing. For you personally, extending the capabilities of IC-CAP means you can realize a significant return on your investment in your IC-CAP software, because you can now customize your environment to tackle whatever measurement challenge you might face.

 

Back to Basics

Before I delve into how to add PyVISA to a virtual Python environment, let’s discuss a few of the basics. First and foremost, the reason this is even possible is because the authors of IC-CAP developed a link between Python and IC-CAP back in 2013. The link provided in the iccap.py module significantly expanded the flexibility and extensibility of the IC-CAP platform. The most common modules for engineering and scientific programming in Python are also currently included in the IC-CAP 2016 Python environment:

  1. Numpy: A fundamental package for numerical analysis including math functions, arrays and matrix operations.
  2. SciPy: A package for scientific and engineering computations.
  3. Matplotlib: A 2D plotting package that outputs plots in multiple popular graphics formats.
  4. PySide: A library that can be used for implementing custom graphical user interfaces using Qt.

 

         

 

Prerequisites

There are a few things you’ll need to do prior to undertaking the installation of the PyVISA package:

  • Install IC-CAP_2016_01 or later, under Windows 7 in the default installation directory, which is typically C:\Keysight\ICCAP_2016_01.
  • Install the Keysight IO Libraries 17.x software and configure it to use the VISA library visa32.dll. This dynamic link library will be installed in the C:\Windows\system32directory.
  • Configure and test communication with your instruments using the Keysight Connection Expert software.                  

If you are new to IC-CAP software or Keysight IO Libraries, you’ll first want to get up to speed by checking out the links at the end of this article. If you are new to Python programming, I suggest you read the “About Python” section and check out the links at the end of this article before attempting this configuration.

 

Why Configure a Virtual Python Environment?

Sometimes, adding an incompatible module to a Python environment can cause it to become corrupted. Since IC-CAP ships with its own Python environment, you’ll have to be careful, or risk having to reinstall IC-CAP if problems arise. One way to avoid this problem is to use a virtual Python environment that can be implemented using two Python packages,"virtualenv" and “virtualenvwrapper-win,” which are designed to make it easy for users to create and manage completely isolated Python environments on the same computer.

 

By installing a separate virtual Python environment in your own user directory, you avoid breaking the IC-CAP installed environment, especially when potentially installing modules not compatible with the Python version shipped with your software. If you later upgrade to a newer version of IC-CAP, or if you need to reinstall the software for any reason, you’ll avoid having to reinstall all your third-party Python packages, assuming you have a backup of your home directory. 

 

The steps I’ve outlined for installing and configuring a virtual Python environment will allow you to install any third-party Python packages you want to use with IC-CAP. Key to this process is the installation of a standalone Python interpreter that includes PIP, a package manager needed to install the virtualenv and virtualenvwrapper-win. Having a stand-alone system Python environment is also great for developing experimental Python scripts and debugging in programming tools outside of the IC-CAP environment.

 

Overview

The following is a high-level overview of the procedure:

  • Install the Python 2.7 system environment
  • Install the virtualenv and virtualenvwrapper-win modules using PIP
  • Create your virtual Python environment for use with IC-CAP
  • Verify your new virtual Python environment
  • Configure the project directory for easy access to IC-CAPs Python interpreter
  • Install the PyVISA package using PIP in the virtual Python environment
  • Take PyVISA for a test drive using the virtual Python environment console
  • Write a macro within IC-CAP to activate the visual Python environment and use PyVISA

 

Step-By-Step Process for Installing the PyVISA Package

 

Step 1: Install the Python 2.7 system environment

Install the latest stable Python 2.7 release, which is currently version 2.7.13. Download Python 2.7.13 for Windows 64-bit from python.org. Python 2.7 is used because Python 3.x is not currently available for IC-CAP. Choose the default installation location, which is “C:\Python27”.

 

                                                                                                

Add the Python 2.7 directories to the Windows PATH environment variable. This may be done through the Environment variables in Windows under the Advancedtab in computer Advanced system settings in Computer properties.

 

NOTE: The username in the command prompt is the name of the current user logged in to your Windows 7 machine. This generic name is a place holder for the commands listed below and represent the current user's home directory. The commands you will need to type are displayed in green throughout this article.

 

Check your Python installation.

 

C:/Users/usernamepython –V

Python 2.7.13

 

Step 2: Install the virtualenv and virtualenvwrapper-win modules using PIP

To installvirtualenv type:

C:> pip install virtualenv

 

This should install virtualenv.exe into the C:\Python27\Scripts directory

 

To installvirtualenvwrapper-win type:

C:> pip install virtualenvwrapper-win

 

This should install a set of useful batch '.bat' files that wrap the virtualenv functions and make creating and

managing virtual Python environments easier. These files should be installed in the C:\Python27\Scripts directory.

 

Check yourvirtualenv installation:

C:> virtualenv –-version

15.1.0

                          

Step 3: Create your virtual Python environment for use with IC-CAP

Create the virtual environment using the virutalenvwrapper-win provided batch file mkvirtualenv and name it icenv.

Type the following at the command prompt:

 

C:\Users\usernamemkvirtualenv -p C:\Keysight\ICCAP_2016_01\tools\win32_64\python.exe icenv

 

NOTE: The -p option allows you to specify the IC-CAP Python 2.7.3 default environment to create our

virtual Python environment. Virtualenv creates the \Envs\icenv directory and copies the specified Python

interpreter and default modules to your \Users\username directory. 

 

Assuming everything succeeds with no errors or warnings, then we should get the following text:

 

Running virtualenv with interpreter C:\Keysight\ICCAP_2016_01\tools\win32_64\python.exe

New python executable in C:\Users\username\Envs\icenv\Scripts\python.exe

Installing setuptools, pip, wheel...done.

 

NOTE: The previous step creates the directory 'C:\Users\username\Envs\icenv' and copies the Python default

environment from C:\Keysight\ICCAP_2016_01\tools\win32_64. The contents of this '\Envs\icenv' directory

will now be the default Python configuration for IC-CAP 2016.

 

Use the cdvirtualenv batch file to easily change the directory to the icenv virtual Python environment we just created.

 

(icenv) C:\Users\username> cdvirtualenv

 

The command prompt should change to the following:

 

(icenv) C:\Users\username\Envs\icenv >

 

NOTE: This is the activated state for the icenv virtual Python environment. The 'activate.bat' file was called

during the mkvirtualenv command, which makes the following changes: 1) Prepending the virtual

environment's path to the Windows 7 system PATH environment variable so that it will be the first Python

interpreter found when searching for the python.exe. 2) Modifies the shell property to display the (icenv), which

denotes the virtual environment that is currently active. If no virtual environment is activated, the system  Python

is active by default.

 

Step 4: Verify your new virtual Python environment

Verify the activated Python 2.7 environment by checking the system path 'sys.path' and system prefix 'sys.prefix'

 

(icenv) C:\Users\username\Envs\icenv> python -V

Python 2.7.3

 

Start the interactive Python interpreter for the virtual environment.

 

(icenv) C:\Users\username\Envs\icenv> python

     

      You should see something like the following:

Python 2.7.3 (default, Feb 1 2013, 15:22:31) [MSC v.1700 64 bit (AMD64)] on win32

Type "help", "copyright", "credits" or "license" from more information.

>>>

 

Now, enter the following commands at the Python interactive prompt:

>>> import sys

>>> print sys.prefix

C:\Users\username\Envs\icenv

>>> print sys.path

['', C:\\Users\<username>\Envs\\icenv\\Scripts\\python27.zip', 

'C:\\Users\\<username>\\Envs\\icenv\\DLLs',
'C:\\Users\\<username>\\Envs\\icenv\\lib',
'C:\\Users\\<username>\\Envs\\icenv\\lib\\plat-win',
'C:\\Users\\<username>\\Envs\\icenv\\lib-tk',
'C:\\Users\\<username>\\Envs\\icenv\\Scripts',

'C:\\Users\\<username>\\Envs\\icenv\\DLLs',
'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\Lib',
'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\DLLs',
'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\lib-tk',
'C:\\Users\\<username>\\Envs\\icenv\\lib\\site-packages'
'C:\\Users\\<username>\\Envs\\icenv\\DLLs',
'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64']

>>> quit()

(icenv) C:\Users\username\Envs\icenv>

 

To exit the icenv virtual environment and return to the system Python environment, type the following at the command prompt:

 

(icenv) C:\Users\username\Envs\icenv> deactivate

C:\Users\username\Envs\icenv>

 

Start the interactive Python interpreter for the system Python

 

C:\Users\username> python

 

You should see something like the following:

Python 2.7.13 (v2.7.3:a06454b1afa1, Dec 17 2016, 20:54:40) [MSC v.1500 64 bit (AMD64)] on win32

Type "help", "copyright", "credits" or "license" from more information.

>>>

 

Now, enter the following commands at the Python interactive prompt:

 

>>> import sys

>>> print sys.prefix

C:\Python27

>>> print sys.path

['','C:\\WINDOWS\\SYSTEM32\\python27.zip', 'C:\\Python27\\DLLs',

'C:\\Python27\\lib', 'C:\\Python27\\lib\\plat-win',  'C:\\Python27\\lib\\lib-tk',

'C:\\Python27', 'C:\\Python27\\lib\\site- packages']

>>> quit()

C:\Users\username>

 

To reactivate the icenv virtual environment, use the virtualenvwrapper batch file 'workon.bat' by typing:

 

C:\Users\username\Envs\icenv> workon icenv

(icenv) C:\Users\username\Envs\icenv>

 

Step 5: Configure the project directory for easy access to IC-CAP’s Python interpreter

Here, we will set the project directory for the icenv virtual environment to IC-CAP's '\tools\win32_64' directory. This makes it easier to execute the built-in Python interpreter and import the IC-CAP included modules and Python tools.

Now you will no longer have to type the full path to access these tools.

 

NOTE: Anything you install using PIP while in the icenv virtual environment will still be installed

in the C:\Users\username\Envs\icenv.

 

Set the project directory to the ICCAP_2016_01 default Python path by typing the following:

 

(icenv) C:\Users\username\Envs\icenv> setprojectdir C:\Keysight\ICCAP_2016_01\tools\win32_64

 

"C:\Keysight\ICCAP_2016_01\tools\win32_64" is now the project directory for virtualenv

"C:\Users\username\Envs\icenv"

 

"C:\Keysight\ICCAP_2016_01\tools\win32_64" added to

C:\Users\username\Envs\icenv\Lib\site-packages\virtual_path_extensions.pth

 

Check that the project directory is set properly.

 

(icenv) C:\Users\username\Envs\icenv> cdproject

(icenv) C:\Keysight\ICCAP_2016_01\tools\wind32_64>

 

Return to the virtual environment directory.

 

(icenv) C:\Keysight\ICCAP_2016_01\tools\wind32_64> cdvirtualenv

(icenv) C:\Users\username\Envs\icenv>

 

Step 6: Install the PyVISA package using PIP in the virtual Python environment

Install PyVISA 1.8 using PIP.

 

(icenv) C:\Users\username\Envs\icenv> pip install pyvisa

 

Check that PyVISA was installed correctly to your (icenv) virtual python environment.

 

(icenv) C:\Users\username> cd C:\Users\username\Envs\icenv\lib\site-packages

(icenv) C:\Users\username\Envs\icenv\lib\site-packages > dir

 

The directory listing should now include the visa.py, visa.pyc, [pyvisa], and [PyVISA-1.8.dist-info] folders.

 

Step 7: Take PyVISA for a test drive using the virtual Python environment console 

You should have already installed the VISA drivers for your interface, either GPIB or PXI, and configured the system to use the software. Perform a "Scan for Instruments" to automatically add the instruments on your system to the VISA resources. Then, start an interactive Python shell and enter the following commands:

 

       (icenv) C:\Users\<username>>\Envs\icenv> python

 

       >>> import sys

       >>> import visa

       >>> print sys.path

        ['',  C:\\Users\<username>\Envs\\icenv\\Scripts\\python27.zip',

       'C:\\Users\\<username>\\Envs\\icenv\\DLLs',

       'C:\\Users\\<username>\\Envs\\icenv\\lib',

       'C:\\Users\\<username>\\Envs\\icenv\\lib\\plat-win',

       'C:\\Users\\<username>\\Envs\\icenv\\lib-tk',

       'C:\\Users\\<username>\\Envs\\icenv\\Scripts',

       'C:\\Users\\<username>\\Envs\\icenv\\DLLs',

       'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\Lib',

       'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\Lib',

       'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\DLLs',

       'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\lib-tk',

       'C:\\Users\\<username>\\Envs\\icenv\\lib\\site-packages',

       'C:\\Users\\<username>\\Envs\\icenv\\DLLs',

       'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64']

 

      >>> rm = visa.ResourceManager()

      >>> print rm

      Resource Manager of Visa Library at C:\Windows\system32\visa32.dll

   

      >>> print rm.list_resources()

      (u'GPIB0::16::INSTR',)

 

NOTE: An instrument was found on interface GPIB0 at address 16. Now quit the Python session and deactivate the virtual Python environment.

 

     >>> quit()

     (icenv) C:\Users\username>\Envs\icenv> deactivate

           

     C:\Users\username>

 

Step 8: Write a macro within IC-CAP to activate the icenv environment and use PyVISA

Open the project \examples\demo_features\5x3_PYTHON_PROGRAMMING\1_py_api_demo.

 

  1. Select the Macros tab.                                                                                                                                                           
  2. Click the “New... button to create a new macro.                                                                                                               
  3. Enter the name _init_pyvisa.                                                                                                                                                                                                                                                                                                                                                                                                        
  4. Select the Python (Local Namespace) radio button for the Macro Type.                                                                                                                                                                                                                                                                           
  5. Enter the following Python code in the editor window.                                                                                                                                                                         

     

  6. In Line #1 make sure to use the path of your home directory (where you created your icenv virtual Python environment), in this case, the 'C\Users\username\Envs\icenv\Scripts\' path.

  7. The script activate_this.py changes the current system PATH to prepend the (icenv) virtual Python environment to the existing PATH environment variable. This makes it the first location searched by the Windows OS when attempting to load a module (i.e., visa). The path entry 'C:\Users\marendall\Envs\icenv\lib\site-packages' will also be prepended to the system PATH environment variable and will be made available to IC-CAP's Python environment.

  8. Line #2 contains the execfile() function, which is called to launch the activate_this.py script. You can view the contents of this file in your favorite text editor or standalone Python IDE.

  9. Line #5 is where we import the visa.py module functionality into our IC-CAP Python environment.

  10. Line #10 gets the default VISA resource manager, which for our system is the visa32.dll installed with the Keysight IO Libraries in the C:\Windows\system32 directory.

  11. Line #13 calls the list_resources() function in the visa32 DLL library to return the current system resources

    previously configured with Keysight Connection Expert. This function returns a list of all the configured

    resources for the system as a Python List.

  12. In line #15 we print the result of the open_resource('GPIB0::16::INSTR') function, which should just return the     string 'GPIB Instrument at GPIB0::16::INSTR' if there are no errors.

  13. Line #17 closes the current communication session.

 

NOTE:  In practice you’ll want to code the statement in line #15 to be something like the following:

sl = rm.open_resource(r), where r is the resource string ('GPIB0::16::INSTR') and sl points to the object of the

opened VISA resource.

 

You can use call functions on this object by typing something like:

sl.write( cmd, termination='\r'), where cmd = "*RST" with the termination='r' being the carriage-return termination character to append to the end of the command string. This command will perform a GPIB reset on the instrument.

 

You can also use other available visa functions listed in the PyVISA docs, like sending: 

gpib_response = sl.read(termination= '\r') to read the response from the instrument's ouput buffer.

 

In a follow-on article I’ll show you how to create a PyVISA wrapper to simplify programming using these common

functions, but we’ll also be writing helper functions to check for instrument errors and display messages to the user.

 

NOTE: You should always close the VISA session when you are done with a resource. Not properly closing the session

will cause errors if you attempt to re-open the same resource later.                      

 

Step 9: Save and execute the macro within IC-CAP

Save the macro in the model file \Users\username\iccap\python\examples\1_py_api_demo.mdl or some other

suitable directory in your home directory.

 

  1. Click the Save button on the main toolbar, or select File->Save As from the main menu.        

  2. Select the macro _init_pyvisa from the Select Macro list.   

  3. Click the Execute button.                                                                                                                                                                                                                     

  4. Check the results of the script execution in the IC-CAP Status Window.                                                                             

                                                                                                

The full content of the status window should read:

 

['C:\\Users\\<username>\\Envs\\icenv\\Lib\\site-packages',

'C:\\Keysight\\ICCAP_2016_01\\bin\\python27.zip',

'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\DLLs',

'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\lib',

'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\lib\\plat-win',

'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\lib\\lib-tk',

'C:\\Keysight\\ICCAP_2016_01\\bin',

'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64',

'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\lib\\site-packages',

'C:\\Keysight\\ICCAP_2016_01\\tools\\win32_64\\Lib',

'C:\\Keysight\\ICCAP_2016_01\\iccap\\lib\\python',

'C:\\Users\\<username>\\iccap\\python']

C:\Users\<username>\Envs\icenv

Resource Manager of Visa Library at C:\Windows\system32\visa32.dll

(u'GPIB0::16::INSTR')

GPIBInstrument at GPIB0::16::INSTR

 

The Bottom Line

If you completed all of these steps successfully, you should now be able access the full capabilities of PyVISA from IC-CAP 2016. That means you can create transforms for instrument control and data acquisition over any supported interface.

 

Hopefully this information will be beneficial to those wanting to customize their IC-CAP 2016 installation to take full advantage of the many powerful Python packages available for download, or to write their own custom Python/PyVISA measurement routines. This method can also be used to install additional virtual Python environments for use with other Keysight products like WaferPro Express 2016. In a future blog post, I’ll outline the steps to do just that. In the meantime, for more information on IC-CAP or Keysight IO Libraries, go to www.keysight.com/find/eesof-iccap and www.keysight.com/find/IOlibraries, respectively.

 

References:

About Python

If you are new to Python programming, here’s some information to help you follow the steps in this blog.  

  • Python is an"interpreted" language, which means it generally executes commands typed by the user in an interactive command shell. This is convenient for testing program statements to learn the Python syntax. However, a more common means of writing a Python program is to create a Python script file with the '.py' extension. Say you created an example program and save it as 'example.py.' To run the program, you simply type 'python example.py' at the command shell prompt.
  • Python scripts, which are often called modules, can also be used for creating libraries of functionality, and are distributed along with program resources in packages.
  • Packages can be installed and combined with user-generated code to extend a program's functionality.  
  • PIP is the Python package installer that integrates with PyPI.orgthe Python Package Index. It is a repository of numerous free Python applications, utilities and libraries. PIP allows you to download and install packages from the package index without manually downloading, uncompressing and installing the package via the command 'python setup.py install'. PIP also checks for package dependencies and automatically downloads and installs those as well. 
  • An environment is a folder (directory) that contains everything a Python project (application) needs to run in an organized, isolated manner. When its initiated, it automatically comes with its own Python interpretera copy of the one used to create italongside its very own PIP. 

 

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